Chris Rider and Eric Rolf - Introduction to Android

7/31/2019 Chris Rider and Eric Rolf - Introduction to Android

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Introduction toAndroidMarch 5, 2012


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Introductions

Speaker:

Chris Rider

Northern Kentucky University

Center for Applied Informatics

Senior Technology Architect

[email protected]

859-572-1302

Assistants: Spencer Egart
mailto:[email protected]:[email protected]


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Resources

http://developer.android.com

Sams Teach Yourself Android Application Development in 24

hours; Lauren Darcey, Shane Conder

Apress Beginning Android; Mark L. Murphy
http://developer.android.com/http://developer.android.com/


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Prerequisites for Android

Development Knowledge of the Java programming language is highly

recommended. If not, previous experience in another Object

Oriented Programming (OOP) language will be helpful

Understanding of OOP concepts. Java is an OOP language and

Android takes full advantage of this. Previous experience with an Integrated Development

Environment (IDE) is helpful, but not required

Windows, Mac, or Linux computer


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Introduction

Android is quickly becoming one of the dominate mobile

platforms.

Android is used in mobile phones, cars, BluRay players,

tablets, and many other consumer electronic devices

Open Handset Alliance formed in 2007 (Google is theprominent member)

In 2008, the Android platform was announced

T-Mobile shipped the G1 in late 2008

There are now over 50 Android phones According to Nielsenwire, Android now has 29% of the US

Market share for smartphones (RIM has 27%; Apple has 27%)

Android embraces open standards


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What is Android?

Android is a software stack for mobile devices that includes an

operating system, middleware and key applications.

The Android SDK provides the tools and APIs necessary to

begin developing applications on the Android platform using

the Java programming language.
http://developer.android.com/sdk/index.htmlhttp://developer.android.com/sdk/index.html


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Android Features

Application framework enabling reuse and replacement ofcomponents

Dalvik virtual machine optimized for mobile devices

Integrated browser based on the open source WebKit engine

Optimized graphics powered by a custom 2D graphics library; 3D

graphics based on the OpenGL ES 1.0 specification (hardwareacceleration optional)

SQLite for structured data storage

Media support for common audio, video, and still image formats(MPEG4, H.264, MP3, AAC, AMR, JPG, PNG, GIF)

GSM Telephony (hardware dependent)

Bluetooth, EDGE, 3G, and WiFi (hardware dependent) Camera, GPS, compass, and accelerometer (hardware dependent)

Rich development environment including a device emulator, toolsfor debugging, memory and performance profiling, and a plugin forthe Eclipse IDE
http://webkit.org/http://webkit.org/


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Android Architecture


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Android Runtime

Android includes a set of core libraries that provides most ofthe functionality available in the core libraries of the Javaprogramming language.

Every Android application runs in its own process, with its owninstance of the Dalvik virtual machine. Dalvik has been writtenso that a device can run multiple VMs efficiently. The DalvikVM executes files in the Dalvik Executable (.dex) format whichis optimized for minimal memory footprint. The VM isregister-based, and runs classes compiled by a Java languagecompiler that have been transformed into the .dex format by

the included "dx" tool. The Dalvik VM relies on the Linux kernel for underlying

functionality such as threading and low-level memorymanagement.


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Linux Kernel

Android relies on Linux version 2.6 for core system services

such as security, memory management, process management,

network stack, and driver model. The kernel also acts as an

abstraction layer between the hardware and the rest of the

software stack.


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Capabilities of Mobile Devices

Internet access

Touch screen

GPS (global positioning system satellite-based system to

determine a location)

Local storage

Camera

Media playback

Phone


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Limitation of Mobile Devices

Screen size

Touch screen

Keyboard? Trackball?

Memory

Storage

Battery Life

Cell network


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Download the Android SDK

http://developer.android.com/sdk/index.html

Choose the file that corresponds to the platform that you will

be developing on
http://developer.android.com/sdk/index.htmlhttp://developer.android.com/sdk/index.html


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Installing the SDK

If you downloaded a .zip or .tgz package (instead of the SDK

installer), unpack it to a safe location on your machine. By

default, the SDK files are unpacked into a directory named

android-sdk-.

If you downloaded the Windows installer (.exe file), run it nowand it will check whether the proper Java SE Development Kit

(JDK) is installed (installing it, if necessary), then install the SDK

Tools into a default location (which you can modify).

Make a note of the name and location of the SDK directory on

your systemyou will need to refer to the SDK directory later,

when setting up the ADT plugin and when using the SDK tools

from command line.


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Adding Platforms and

Components The last step in setting up your SDK is using theAndroid SDK and AVD Manager(a tool

included in the SDK starter package) to download essential SDK components into yourdevelopment environment.

The SDK uses a modular structure that separates the major parts of the SDKAndroidplatform versions, add-ons, tools, samples, and documentationinto a set of separatelyinstallable components. The SDK starter package, which you've already downloaded,includes only a single component: the latest version of the SDK Tools. To develop anAndroid application, you also need to download at least one Android platform and the SDK

Platform-tools (tools that the latest platform depend upon). However, downloadingadditional components is highly recommended.

If you used the Windows installer, when you complete the installation wizard, it will launchthe Android SDK and AVD Manager with a default set of platforms and other componentsselected for you to install. Simply click Install to accept the recommended set ofcomponents and install them. You can then skip to Step 5, but we recommend you first readthe section about the Available Components to better understand the componentsavailable from the Android SDK and AVD Manager.

You can launch the Android SDK and AVD Manager in one of the following ways: From within Eclipse, select Window > Android SDK and AVD Manager.

On Windows, double-click the SDK Manager.exe file at the root of the Android SDKdirectory.

On Mac or Linux, open a terminal and navigate to the tools/ directory in the Android SDK,then execute: android
http://developer.android.com/sdk/installing.htmlhttp://developer.android.com/sdk/installing.htmlhttp://developer.android.com/sdk/installing.htmlhttp://developer.android.com/sdk/installing.htmlhttp://developer.android.com/sdk/installing.htmlhttp://developer.android.com/sdk/installing.html


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Android SDK and AVD

Manager After launching the

menu, select Availablepackages->AndroidRepository

It is recommended toinstall all of theselected options

Click the Install

Selected button Installing all options

could take a while


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Introducing Eclipse

Eclipse is a popular opensource IDE used for Java, C,C++, and other programminglanguages

Eclipse is supported onseveral platforms including

Windows, Linux, and Mac Eclipse was created in 2001 by

IBM

Download it for free:http://eclipse.org/downloads,its recommended that you

choose Eclipse Classic. Eclipse supports templates

which allows it to beconfigured
http://eclipse.org/downloadshttp://eclipse.org/downloadshttp://eclipse.org/downloads


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Configuring Eclipse

Select a defaultlocation for yourprojects

Eclipse calls this yourworkspace

Typically, the defaultrecommendationfrom Eclipse is OKhowever, you cancustomize thelocation


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ADT Plugin

The ADT Plugin is the Android Developer Template plugin

The ADT Plugin configures Eclipse for Android software

development

It includes modifications to the text editor, installs simulators

(modules to run your Android software on if you do not havean Android device), and other tools to assist with

development tasks


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Installing the ADT Plugin

Start Eclipse, then select Help > Install New Software....

Click Add, in the top-right corner.

In the Add Repository dialog that appears, enter "ADT Plugin"for the Name and the following URL for the Location:

https://dl-ssl.google.com/android/eclipse/ Note: If you havetrouble acquiring the plugin, try using "http" in the LocationURL, instead of "https" (https is preferred for securityreasons).

Click OK.

In the Available Software dialog, select the checkbox next toDeveloper Tools and click Next.

In the next window, you'll see a list of the tools to bedownloaded. Click Next.

Read and accept the license agreements, then click Finish.

When the installation completes, restart Eclipse.


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Configuring the ADT Plugin

Once you've successfully downloaded ADT as described

above, the next step is to modify your ADT preferences in

Eclipse to point to the Android SDK directory:

Select Window > Preferences... to open the Preferences panel

(Mac OS X: Eclipse > Preferences). Select Android from the left panel.

For the SDK Location in the main panel, click Browse... and

locate your downloaded SDK directory.

Click Apply, then OK. Restart Eclipse.


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Project One: Hello World

It is a tradition tocreate Hello Worldas the first projectwhen learning a new

platform This project will

introduce the AndroidVirtual Device (AVD),using Eclipse, andverify that all of thesoftware we installedis working correctly


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Creating an AVD

In this tutorial, you will run your application in the Android Emulator.Before you can launch the emulator, you must create an AndroidVirtual Device (AVD). An AVD defines the system image and devicesettings used by the emulator.

To create an AVD:

In Eclipse, choose Window > Android SDK and AVD Manager.

Select Virtual Devices in the left panel.

Click New.

The Create New AVD dialog appears.

Type the name of the AVD, such as "my_avd".

Choose a target. The target is the platform (that is, the version of the

Android SDK, such as 2.2) you want to run on the emulator. In the SD Card field, enter a size of 1024 MiB.

You can ignore the rest of the fields for now.

Click Create AVD.


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Create a New Android Project

After you've created an AVD, thenext step is to start a newAndroid project in Eclipse.

1. From Eclipse, select File > New >Project. If the ADT Plugin forEclipse has been successfullyinstalled, the resulting dialog

should have a folder labeled"Android" which should contain"Android Project". (After youcreate one or more Androidprojects, an entry for "AndroidXML File" will also be available.)

2. Select "Android Project" and click

Next.


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Create a New Android Project

(contd)1.Fill in the project

details with thefollowing values: Project name:

HelloAndroid

Application name:Hello, Android

Package name:com.example.helloandroid (or your ownprivate namespace)

Create Activity:HelloAndroid

2.Click Finish.


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Package Explorer

The Package Explorershows the layout ofyour Androidprojects.

It allows you to viewthe source files,generated files, andother items you

might use in a project(such as graphics,audio, etc.)


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HelloAndroid.java

package com.example.helloandroid;

import android.app.Activity;

import android.os.Bundle;

public class HelloAndroid extends Activity {

/** Called when the activity is first created. */

@Override

public void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);setContentView(R.layout.main);

}

}


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Activity class

public class HelloAndroid extends Activity

Notice that the HelloAndroid class we created extends the

Activity class.

An Activity is a single application entity that is used to perform

actions. An application may have many separate activities, but the user

interacts with them one at a time.


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OnCreate method


super.onCreate(savedInstanceState);

setContentView(R.layout.main);

}

The onCreate() method will be called by the Android system

when your Activity starts it is where you should perform all

initialization and UI setup. An activity is not required to have a

user interface, but usually will.

Now let's modify some code!
http://developer.android.com/reference/android/app/Activity.htmlhttp://developer.android.com/reference/android/app/Activity.html


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Construct the UI

package com.example.helloandroid;

import android.app.Activity;import android.os.Bundle;import android.widget.TextView;

public class HelloAndroid extends Activity {

/** Called when the activity is first created. */@Overridepublic void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);TextView tv = new TextView(this);tv.setText("Hello, Android");setContentView(tv);

}

} Add the bold, italic text to your HelloAndroid.java file.

As you are typing, you will notice that Eclipse uses code completion this is ahandy feature of modern IDEs that can save a programmer time (and minimizelooking up specific methods a call, such as TextView, supports)


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Android Views

An Android user interface is composed of hierarchies of objects calledViews. A View is a drawable object used as an element in your UI layout,such as a button, image, or (in this case) a text label. Each of theseobjects is a subclass of the View class and the subclass that handles textis TextView.

In this change, you create a TextView with the class constructor, which

accepts an Android Context instance as its parameter. A Context is ahandle to the system; it provides services like resolving resources,obtaining access to databases and preferences, and so on. The Activityclass inherits from Context, and because your HelloAndroid class is asubclass of Activity, it is also a Context. So, you can pass this as yourContext reference to the TextView.

Next, you define the text content with setText().

Finally, you pass the TextView to setContentView() in order to display itas the content for the Activity UI. If your Activity doesn't call thismethod, then no UI is present and the system will display a blankscreen.

There it is "Hello, World" in Android! The next step, of course, is tosee it running.
http://developer.android.com/reference/android/view/View.htmlhttp://developer.android.com/reference/android/view/View.htmlhttp://developer.android.com/reference/android/widget/TextView.htmlhttp://developer.android.com/reference/android/widget/TextView.htmlhttp://developer.android.com/reference/android/content/Context.htmlhttp://developer.android.com/reference/android/content/Context.htmlhttp://developer.android.com/reference/android/widget/TextView.htmlhttp://developer.android.com/reference/android/app/Activity.htmlhttp://developer.android.com/reference/android/app/Activity.htmlhttp://developer.android.com/reference/android/widget/TextView.htmlhttp://developer.android.com/reference/android/content/Context.htmlhttp://developer.android.com/reference/android/widget/TextView.htmlhttp://developer.android.com/reference/android/view/View.html


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Running Hello World

The Eclipse plugin makes it easyto run your applications:

Select Run > Run.

Select "Android Application".

The Eclipse plugin automaticallycreates a new run configurationfor your project and thenlaunches the Android Emulator.Depending on your environment,the Android emulator might takeseveral minutes to boot fully, soplease be patient. When theemulator is booted, the Eclipseplugin installs your application

and launches the default Activity.You should now see somethinglike this:


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If Hello World doesnt run

While working on this presentation, I could not get Hello

Android to run. The emulator would start, but my app never

installed

I found this on the Android Portal:

Quit the emulator if it is running Check that any emulator processes are killed (sometimes they

can hang, use ps on unix or mac, or task manager in the process

view on windows).

Quit Eclipse

From the command line, type: adb kill-server

Start Eclipse and try again

This solved the problem.


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The AVD

Home button

Menu button

Back button

App button


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Eclipse Shortcuts

Launch Wizards

Android SDK and

AVD Manager Android Debugger

Run


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Eclipse Console

The console is useful to see what is happening when you run

your Android program

It can show informational, warning, or error messages you

might encounter


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Outside of class

Hour 2: Mastering the Android Development Tools (in the

SAMS Teach Yourself Android in 24 hours) is not covered in

detail in this training session.

It is recommended that you read over this chapter as it

contains a lot of useful information.


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What is an application?

An application is a collection of tasks.

Each task is called an activity.

Each activity within an application has a unique purpose and

user interface.

Example game: Chippys Revenge has five screens

Splash startup screen, game logo, sound

Menu user can choose options to play game, view scores, read

help

Play The screen where the user plays the game Scores screen displays high scores

Help screen displays instructions for playing the game

l


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Application Activity

Requirements Chippys Revenge would have five activity classes

SplashActivity - This activity serves as the default activity to launch. Itsimply displays a layout (maybe just a big graphic), plays music forseveral seconds, and then launches MenuActivity.

MenuActivityThis activity is pretty straightforward. Its layout hasseveral buttons, each corresponding to a feature of the application.

The onClick() handlers for each button trigger cause the associatedactivity to launch.

PlayActivityThe real application guts are implemented here. Thisactivity needs to draw stuff onscreen, handle various types of userinput, keep score, and generally follow whatever game dynamics thedeveloper wants to support.

ScoresActivityThis activity is about as simple as SplashActivity. Itdoes little more than load a bunch of scoring information into aTextView control within its layout.

HelpActivityThis activity is almost identical to ScoresActivity, exceptthat instead of displaying scores, it displays help text. Its TextViewcontrol might possibly scroll.


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Application Context

The application context is the central location for all top-level

application functionality. You use the application context to

access settings and resources shared across multiple activity

instances.

You can retrieve the application context for the currentprocess by using the getApplicationContext() method, like this:

Context context = getApplicationContext();

Because the Activity class is derived from the Context class,

you can use this instead of retrieving the application context

explicitly.

Once you have retrieved a valid application context, you can

use it to access application-wide features and services.

R i i A li i


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Retrieving Application

Resources You can retrieve application resources by using the

getResources() method of the application context. The most

straightforward way to retrieve a resource is by using its

unique resource identifier, as defined in the automatically

generated R.java class. The following example retrieves aString instance from the application resources by its resource

ID:

String greeting = getResources().getString(R.string.hello);

A i A li i


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Accessing Application

Preferences You can retrieve shared application preferences by using the

getSharedPreferences() method of the application context.

You can use the SharedPreferences class to save simple

application data, such as configuration settings. Each

SharedPreferences object can be given a name, allowing youcan organize preferences into categories or store preferences

all together in one large set.

For example, you might want to keep track of each users

name and some simple game state information, such as

whether the user has credits left to play. The following codecreates a set of shared preferences called GamePrefs and

saves a few such preferences:


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Preferences Samples

SharedPreferences settings =

getSharedPreferences(GamePrefs, MODE_PRIVATE);

SharedPreferences.Editor prefEditor = settings.edit();

prefEditor.putString(UserName, Spunky);

prefEditor.putBoolean(HasCredits, true);

prefEditor.commit();

To retrieve preference settings, you simply retrieve

SharedPreferences and read the values back out:

SharedPreferences settings =getSharedPreferences(GamePrefs, MODE_PRIVATE);

String userName = settings.getString(UserName, Chippy Jr.

(Default));

A i O h A li i


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Accessing Other Application

Functionality Using Contexts The application context provides access to a number of top-

level application features. Here are a few more things you can

do with the application context:

Launch Activity instances

Retrieve assets packaged with the application Request a system-level service provider (location service)

Manage private application files, directories, and databases

Inspect and enforce application permissions

The most common use is launching Activity instances


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Working with Activities

The Activity class is central to every Android application.

Much of the time, youll define and implement an activity for

each screen in your application.


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Launching Activities

There are a number of ways to launch an activity, including the

following:

Designation a launch activity in the manifest file

Launching an activity using the application context

Launching a child activity from a parent activity for a result

D i ti L h A ti it


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Designating a Launch Activity

in the Manifest file Each Android application must designate a default activity

within the Android manifest file

Inspect the file AndroidManifest.xml from the Hello Android

project. Click on the Application tab, scroll down until you see

Application Nodes. Note the default activity is HelloAndroid.

L hi A ti iti U i th


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Launching Activities Using the

Application Context The most common way to launch an activity is to use the

startActivity() method of the application context. This method

takes one parameter, called an intent. We will talk more about

the intent in a moment, but for now, lets look at a simple

startActivity() call.

The following code calls the startActivity() method with an

explicit intent:

startActivity(new Intent(getApplicationContext(),

MenuActivity.class));

L hi A ti it f


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Launching an Activity for a

Result Sometimes an activity wants to launch a related activity and

get the result, instead of launching an entirely independent

activity. In this case, you can use the

Activity.startActivityForResult() method.

The result will be returned in the Intent parameter of thecalling activitys onActivityResult() method.

We will talk more about how to pass data using an Intent

parameter in a moment.


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Managing Activity State

Applications can be interrupted when various higher-priority

events, such as phone calls, take precedence.

There can be only one active application at a time; specifically,

a single application activity can be in the foreground at any

given time. Your apps should prepare for the unexpected

Save state

Resume


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Activity Callbacks

The Activity class has a number of callbacks that provide an

opportunity for an activity to respond to events such as

suspending and resuming.

onCreate() called when an activity starts/restarts

onResume() called when an activity becomes the foregroundactivity

onPause() called when an activity leaves the foreground

onDestroy() called when an application is shutting down


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Diagram of Callback Methods


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Working with Intents

An intent is an abstract description of an operation to be

performed.

An Intent object encapsulates a task request used by the

Android operating system.

When the startActivity() method is called with the Intentparameter, the Android system matches the Intent action with

appropriate activity on the Android system.

That activity is then launched.

Passing Information with


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Passing Information with

Intents Intents can be used to pass data between activities. You can

use an intent in this way by including additional data, called

extras, within the intent.

To package extra pieces of data along with an intent, you use

the putExtra() method with the appropriate type of object youwant to include.

The Android programming convention for intent extras is to

name each one with the package prefix (for example,

com.androidbook.chippy.NameOfExtra).

Intent intent = new Intent(getApplicationContext(),HelpActivity.class);

intent.putExtra(com.androidbook.chippy.LEVEL, 23);

startActivity(intent);

Using Intents to Launch Other


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Using Intents to Launch Other

Applications Applications can launch external activity classes in other

applications

Examples:

Launching the built-in web browser and supplying a URL address

Launching the web browser and supplying a search string Launching the built-in Dialer application and supplying a phone

number

Launching the built-in Maps application and supplying a location

Launching Google Street View and supplying a location

Launching the built-in Camera application in still or video mode

Launching a ringtone picker

Recording a sound


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Intent Code Sample

Uri address = Uri.parse(http://www.perlgurl.org);

Intent surf = new Intent(Intent.ACTION_VIEW, address);

startActivity(surf);


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Working with Dialogs

Handset screens are small, and user interface real estate isvaluable.

Sometimes you want to handle a small amount of user

interaction without creating an entirely new activity.

In such instances, creating an activity dialog can be veryhandy.

Dialogs can be helpful for creating very simple user interfaces

that do not necessitate an entirely new screen or activity to

function.

Instead, the calling activity dispatches a dialog, which can have

its own layout and user interface, with buttons and input

controls.

Dialog Methods of the Activity


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Dialog Methods of the Activity

Class Activity.showDialog() - Shows a dialog, creating it if necessary.

Activity.onCreateDialog() - Is a callback when a dialog is being

created for the first time and added to the activity dialog pool.

Activity.onPrepareDialog() - Is a callback for updating a dialog

on-the-fly. Dialogs are created once and can be used manytimes by an activity. This callback enables the dialog to be

updated just before it is shown for each showDialog() call.

Activity.dismissDialog() - Dismisses a dialog and returns to the

activity. The dialog is still available to be used again by calling

showDialog() again.

Activity.removeDialog() - Removes the dialog completely from

the activity dialog pool.


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Outside of class

Hour 4: Managing Application Resources (in the SAMS TeachYourself Android in 24 hours) is not covered in detail in this

training session.

Hour 5: Configuring the Android Manifest Files is not covered

in detail in this training session It is recommended that you read over these chapters as they

contain a lot of useful information.

Project Two: Hello World


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Project Two: Hello World

Advanced This project is a variation on project one.

It introduces the Graphic Layout, resources, using a button,

and seeing an alert


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Create a new project

From Eclipse, File->New->Project

From the Wizard

screen, selectAndroid Project


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Examine R.java

R.java is a generatedfile.

Do not modify this

file your changeswill be lost!

This file has

references to data

used by apps such asicons, images,

strings, etc.


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Strings.xml

Under the res folder,expand the values folder.

Double-click on strings.xmlto all Eclipse to edit thefile.

In the editor window, thereis a tab labeled Resourcesand another tab labeledstrings.xml.

Resources is the simplerview it hides the XML

data and shows thedefined strings.

The strings.xml view is theraw XML.


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Run the app

Without making anycode changes, the

app displays the

message.

Feel free to modify

Strings.xml and

experiment with

different strings.


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Main.xml

Under the res folder,expand the layoutfolder.

Double-click onmain.xml

This will open theGraphical Layout editor

Note the tabs at thebottom of the screen:

Graphical Layout andmain.xml


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Lets add a button

While in theGraphical Layoutmode, drag a Buttonobject to the view

screen. Double-click on the

Button this willcause Eclipse to go to

the main.xml view. Change the text for

Button to Alert


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Run the app

You will see the button on the screen.

If you click the button, nothing happens.

Lets add some code to make something happen.

Double-click on HelloWorldAndroid.java so we can make some

changes.

Lets make the button do


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Let s make the button do

something Buttons must register with a Listener.

A Listener detects specific events in a program such as a

button press.

We are using the OnClickListener() method when this is

detected, we are then calling a method we create calledonClick().

The onClick method executes some code.

In the example we are implementing, we are going to use the

Toast framework to display a Toast.

A Toast is a short message that automatically exits once its

timer expires.

Sample code that implements


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Sample code that implements

the onClick() method

package com.test.helloworldadvanced;


import android.content.Context;


import android.view.View;

import android.view.View.OnClickListener;

import android.widget.Button;

import android.widget.Toast;

public class HelloWorldAdvanced extends Activity {

private Button alertButton;


@Override




alertButton = (Button)this.findViewById(R.id.button1);

alertButton.setOnClickListener(new OnClickListener() {

public void onClick(View v) {

Context context = getApplicationContext(); CharSequence text = "Hello toast!";

int duration = Toast.LENGTH_SHORT;

Toast toast = Toast.makeText(context, text, duration);

toast.show();

}

});

}

}


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Run the app

Pressing the Alertbutton will cause the

Toast to display.

Notice that the Toast

exits after a few

seconds without

additional work.

Toasts are often usedas informational

messages or notices.


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Project Three: Web views

This project will introduce web views.

Web views are used to view web pages and local HTML files

(very useful for help files.)

We will cover loading a web page from a URL and from a local

HTML file.


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Create a new project

Call the projectWebDemo

Build Target: Android2.1-update1

Application Name:WebDemo

Package Name:com.test.webdemo

Create Activity:WebDemo

Min SDK Version: 7


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Edit res/layout/main.xml

Remove the LinearLayout and TextView sections.

Add the WebView section to your main.xml (copy/paste)

t


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src/com.test.webdemo/WebD

emo.java Below the line thatstarts with public

class WebDemo,

type WebView

mWebView.

WebView is the

Android class for a

web view. Notice the red X on

the left hand side.

Lets let the tools fix the


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Let s let the tools fix the

problem Hover your mouse

over the underlined

text WebView

You will see a pop-up

that suggests some

quick fixes.

Select Import

the error is resolved!

Now modify the onCreate()


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Now, modify the onCreate()

method public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState);


mWebView = (WebView) findViewById(R.id.webview); mWebView.getSettings().setJavaScriptEnabled( true);

mWebView.loadUrl("http://www.google.com");

}

This initializes the member WebView with the one from the

Activity layout; requests a WebSettings object withgetSettings(); and enables JavaScript for the WebView withsetJavaScriptEnabled(boolean). Finally, an initial web page isloaded with loadUrl(String).

Modify the
http://developer.android.com/reference/android/webkit/WebView.htmlhttp://developer.android.com/reference/android/app/Activity.htmlhttp://developer.android.com/reference/android/webkit/WebSettings.htmlhttp://developer.android.com/reference/android/webkit/WebView.htmlhttp://developer.android.com/reference/android/webkit/WebView.htmlhttp://developer.android.com/reference/android/webkit/WebSettings.htmlhttp://developer.android.com/reference/android/webkit/WebView.htmlhttp://developer.android.com/reference/android/webkit/WebView.htmlhttp://developer.android.com/reference/android/webkit/WebSettings.htmlhttp://developer.android.com/reference/android/webkit/WebView.htmlhttp://developer.android.com/reference/android/webkit/WebView.htmlhttp://developer.android.com/reference/android/webkit/WebSettings.htmlhttp://developer.android.com/reference/android/app/Activity.htmlhttp://developer.android.com/reference/android/webkit/WebView.html


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Modify the

AndroidManifest.xml Because this application needs access to the Internet, you

need to add the appropriate permissions to the Android

manifest file. Open the AndroidManifest.xml file and add the

following as a child of the element:

While you're in the manifest, give some more space for web

pages by removing the title bar, with the "NoTitleBar" theme:


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AndroidManifest.xml

h


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Project Three Part Two

This lab will expand the Web View so you can display HTMLfrom a local data source.

Create a new project called WebViewFromFile

Project Name: WebViewFromFile

Build Target: Android 2.1-update1 Application Name: WebViewFromFile

Package name: com.test.webviewfromfile

Create Activity: WebViewFromFile

Min SDK Version: 7

l


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Eclipse note

Note the PackageExplorer in Eclipse

This allows you to

manage multiple

projects

It is recommended

you click the left

hand arrow tocollapse projects we

are not working on.

M d f A d dM f l


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Modify AndroidManifest.xlm

Since we are reading from a local html file, we technically donot need to add the permission

android.permission.INTERNET

It is a good practice to only give permissions that are required.

To theme the browser, add the following:

L i l HTML fil


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Lets create a simple HTML file

In your project, go to the assets folder.

Right-click on assets, select new file.

For the file name, choose hello.html this creates an empty

file.

Right-click on hello.html, select Open With->Text Edit Type the following:

Hello HTML

Now, save the file.

L dif i l


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Lets modify main.xml

We are going to add aWebView to our project.Modifyres/layout/main.xml

Click on the Graphical

Layout tab On the left hand side,

open the Compositefolder.

Drag a WebView object

to to interface screen onthe right hand side.

(Remove any stray hellostrings if they exist)

Cli k h i l b


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Click on the main.xml tab

Make not of the id.

It will be similar to id=@+id/webkitWebView1

Now, edit


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Now, edit

WebViewFromFile.java

package com.test.webviewfromfile;



import android.webkit.WebView;

public class WebViewFromFile extends Activity {

WebView browser;


@Override




browser=(WebView)findViewById(R.id. webkitWebView1);

browser.loadUrl("file:///android_asset/hello.html"); }

}

Notice how we set the URL for the browser. File:/// instructs the browser is is reading from a fileinstead of the internet.

The android_asset tells it look in the asset folder for a file named hello.html.

R th
http://localhost/http://localhost/


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Run the program

N t d T t i l


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Notepad Tutorial

The next three projects cover the Notepad Tutorial from the Androiddeveloper portal

Project Four: Construct a simple notes list that lets the user add

new notes but not edit them. Demonstrates the basics of ListActivity

and creating and handling menu options. Uses a SQLite database to

store the notes. Project Five: Add a second Activity to the application. Demonstrates

constructing a new Activity, adding it to the Android manifest,

passing data between the activities, and using more advanced

screen layout. Also shows how to invoke another Activity to return a

result, using startActivityForResult(). Project Six: Add handling of life-cycle events to the application, to

let it maintain application state across the life cycle.

P j t F N t d 1


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Project Four: Notepad 1

In this exercise, you will construct a simple notes list that letsthe user add new notes but not edit them. The exercise

demonstrates:

The basics of ListActivities and creating and handling menu

options.

How to use a SQLite database to store the notes.

How to bind data from a database cursor into a ListView using

a SimpleCursorAdapter.

The basics of screen layouts, including how to lay out a list

view, how you can add items to the activity menu, and how

the activity handles those menu selections.

St 1


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Step 1

Open up the Notepadv1 project in Eclipse. Notepadv1 is a project that is provided as a starting point. It takes care of some

of the boilerplate work that you have already seen if you followed the Hello,World tutorial.

Start a new Android Project by clicking File > New > Android Project.

In the New Android Project dialog, select Create project from existing source.

Click Browse and navigate to where you copied the NotepadCodeLab

(downloaded during setup) and select Notepadv1. The Project Name and other properties should be automatically filled for you.

You must select the Build Targetwe recommend selecting a target with thelowest platform version available. Also add an integer to the Min SDK Versionfield that matches the API Level of the selected Build Target.

Click Finish. The Notepadv1 project should open and be visible in your Eclipsepackage explorer.

If you see an error about AndroidManifest.xml, or some problems related to anAndroid zip file, right click on the project and select Android Tools > Fix ProjectProperties. (The project is looking in the wrong location for the library file, thiswill fix it for you.)

St 2
http://developer.android.com/resources/tutorials/hello-world.htmlhttp://developer.android.com/resources/tutorials/hello-world.htmlhttp://developer.android.com/resources/tutorials/hello-world.htmlhttp://developer.android.com/resources/tutorials/hello-world.htmlhttp://developer.android.com/resources/tutorials/notepad/index.htmlhttp://developer.android.com/resources/tutorials/notepad/index.htmlhttp://developer.android.com/resources/tutorials/notepad/index.htmlhttp://developer.android.com/resources/tutorials/hello-world.htmlhttp://developer.android.com/resources/tutorials/hello-world.html


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Step 2a

Take a look at the NotesDbAdapter class this class is provided toencapsulate data access to a SQLite database that will hold our notesdata and allow us to update it.

At the top of the class are some constant definitions that will be used inthe application to look up data from the proper field names in thedatabase. There is also a database creation string defined, which is usedto create a new database schema if one doesn't exist already.

Our database will have the name data, and have a single table callednotes, which in turn has three fields: _id, title and body. The _id isnamed with an underscore convention used in a number of places insidethe Android SDK and helps keep a track of state. The _id usually has tobe specified when querying or updating the database (in the columnprojections and so on). The other two fields are simple text fields thatwill store data.

The constructor for NotesDbAdapter takes a Context, which allows it tocommunicate with aspects of the Android operating system. This is quitecommon for classes that need to touch the Android system in some way.The Activity class implements the Context class, so usually you will justpass this from your Activity, when needing a Context.

St 2b


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Step 2b

The open() method calls up an instance of DatabaseHelper, which is our local implementation ofthe SQLiteOpenHelper class. It calls getWritableDatabase(), which handles creating/opening adatabase for us.

close() just closes the database, releasing resources related to the connection.

createNote() takes strings for the title and body of a new note, then creates that note in thedatabase. Assuming the new note is created successfully, the method also returns the row _idvalue for the newly created note.

deleteNote() takes a rowIdfor a particular note, and deletes that note from the database.

fetchAllNotes() issues a query to return a Cursor over all notes in the database. The query() call is

worth examination and understanding. The first field is the name of the database table to query(in this case DATABASE_TABLE is "notes"). The next is the list of columns we want returned, in thiscase we want the _id, title and body columns so these are specified in the String array. Theremaining fields are, in order: selection, selectionArgs, groupBy, having and orderBy. Having theseall null means we want all data, need no grouping, and will take the default order. SeeSQLiteDatabase for more details.

Note: A Cursor is returned rather than a collection of rows. This allows Android to use resourcesefficiently -- instead of putting lots of data straight into memory the cursor will retrieve andrelease data as it is needed, which is much more efficient for tables with lots of rows.

fetchNote() is similar to fetchAllNotes() but just gets one note with the rowIdwe specify. It uses aslightly different version of the SQLiteDatabase query() method. The first parameter (set true)indicates that we are interested in one distinct result. The selection parameter (the fourthparameter) has been specified to search only for the row "where _id =" the rowIdwe passed in. Sowe are returned a Cursor on the one row.

And finally, updateNote() takes a rowId, title and body, and uses a ContentValues instance toupdate the note of the given rowId.

St 3
http://developer.android.com/reference/android/database/Cursor.htmlhttp://developer.android.com/reference/android/database/sqlite/SQLiteDatabase.htmlhttp://developer.android.com/reference/android/database/sqlite/SQLiteDatabase.htmlhttp://developer.android.com/reference/android/database/sqlite/SQLiteDatabase.htmlhttp://developer.android.com/reference/android/content/ContentValues.htmlhttp://developer.android.com/reference/android/content/ContentValues.htmlhttp://developer.android.com/reference/android/database/sqlite/SQLiteDatabase.htmlhttp://developer.android.com/reference/android/database/sqlite/SQLiteDatabase.htmlhttp://developer.android.com/reference/android/database/Cursor.html


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Step 3

Open the notepad_list.xml file in res/layout and take a look atit. (You may have to hit thexmltab, at the bottom, in order toview the XML markup.)

This is a mostly-empty layout definition file. Here are somethings you should know about a layout file:

All Android layout files must start with the XML header line:.

The next definition will often (but not always) be a layoutdefinition of some kind, in this case a LinearLayout.

The XML namespace of Android should always be defined in

the top level component or layout in the XML so that android:tags can be used through the rest of the file:xmlns:android="http://schemas.android.com/apk/res/android"

St 4


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Step 4a

We need to create the layout to hold our list. Add code inside of theLinearLayout element so the whole file looks like this:

Step 4b


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Step 4b

The @ symbol in the id strings of the ListView and TextView tags meansthat the XML parser should parse and expand the rest of the id stringand use an ID resource.

The ListView and TextView can be thought as two alternative views, onlyone of which will be displayed at once. ListView will be used when thereare notes to be shown, while the TextView (which has a default value of"No Notes Yet!" defined as a string resource in res/values/strings.xml)

will be displayed if there aren't any notes to display. The list and empty IDs are provided for us by the Android platform, so,

we must prefix the id with android: (e.g., @android:id/list).

The View with the empty id is used automatically when the ListAdapterhas no data for the ListView. The ListAdapter knows to look for thisname by default. Alternatively, you could change the default empty view

by using setEmptyView(View) on the ListView. More broadly, theandroid.R class is a set of predefined resources provided for you by theplatform, while your project's R class is the set of resources your projecthas defined. Resources found in the android.R resource class can beused in the XML files by using the android: name space prefix (as we seehere).

Step 5
http://developer.android.com/reference/android/widget/ListAdapter.htmlhttp://developer.android.com/reference/android/widget/AdapterView.htmlhttp://developer.android.com/reference/android/widget/AdapterView.htmlhttp://developer.android.com/reference/android/widget/ListAdapter.html


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Step 5

To make the list of notes in the ListView, we also need to define a Viewfor each row:

Create a new file under res/layout called notes_row.xml.

Add the following contents (note: again the XML header is used, and thefirst node defines the Android XML namespace) This is the View that will be

used for each notes title row it has only one text field in it.

In this case we create a new id called text1. The + after the @ in the idstring indicates that the id should be automatically created as a resource

if it does not already exist, so we are defining text1 on the fly and thenusing it.

Save the file.

Open the R.java class in the project and look at it, you should see newdefinitions for notes_row and text1 (our new definitions) meaning wecan now gain access to these from the our code.

Step 6


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Step 6

Next, open the Notepadv1 class in the source. In the following steps, we aregoing to alter this class to become a list adapter and display our notes, and alsoallow us to add new notes.

Notepadv1 will inherit from a subclass of Activity called a ListActivity, which hasextra functionality to accommodate the kinds of things you might want to dowith a list, for example: displaying an arbitrary number of list items in rows onthe screen, moving through the list items, and allowing them to be selected.

Take a look through the existing code in Notepadv1 class. There is a currently anunused private field called mNoteNumber that we will use to create numberednote titles.

There are also three override methods defined: onCreate,onCreateOptionsMenu and onOptionsItemSelected; we need to fill these out:

onCreate() is called when the activity is started it is a little like the "main"method for an Activity. We use this to set up resources and state for the activitywhen it is running.

onCreateOptionsMenu() is used to populate the menu for the Activity. This isshown when the user hits the menu button, and has a list of options they canselect (like "Create Note").

onOptionsItemSelected() is the other half of the menu equation, it is used tohandle events generated from the menu (e.g., when the user selects the "CreateNote" item).

Step 7


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Step 7

Change the inheritance of Notepadv1 from Activity toListActivity:

public class Notepadv1 extends ListActivity Note: you will have

to import ListActivity into the Notepadv1 class using Eclipse,

ctrl-shift-O on Windows or Linux, or cmd-shift-O on the Mac

(organize imports) will do this for you after you've written the

above change.

Step 8a


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Step 8a

Fill out the body of the onCreate() method. Here we will set the title for the Activity (shown at the top of the

screen), use the notepad_list layout we created in XML, set up theNotesDbAdapter instance that will access notes data, and populate thelist with the available note titles:

In the onCreate method, call super.onCreate() with thesavedInstanceState parameter that's passed in.

Call setContentView() and pass R.layout.notepad_list.

At the top of the class, create a new private class field called mDbHelperof class NotesDbAdapter.

Back in the onCreate method, construct a new NotesDbAdapterinstance and assign it to the mDbHelper field (pass this into theconstructor for DBHelper)

Call the open() method on mDbHelper to open (or create) the database.

Finally, call a new method fillData(), which will get the data andpopulate the ListView using the helper we haven't defined thismethod yet.

Step 8b


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Step 8b

onCreate() should now look like this: @Override



setContentView(R.layout.notepad_list);

mDbHelper = new NotesDbAdapter(this);

mDbHelper.open();

fillData();

}

And be sure you have the mDbHelper field definition (rightunder the mNoteNumber definition):

private NotesDbAdapter mDbHelper;

Step 9


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Step 9

Fill out the body of the onCreateOptionsMenu() method. We will now create the "Add Item" button that can be accessed by pressing the menu

button on the device. We'll specify that it occupy the first position in the menu.

In strings.xml resource (under res/values), add a new string named "menu_insert" with itsvalue set to Add Item: Add Item Then save the fileand return to Notepadv1.

Create a menu position constant at the top of the class: public static final int INSERT_ID =Menu.FIRST;

In the onCreateOptionsMenu() method, change the super call so we capture the booleanreturn as result. We'll return this value at the end.

Then add the menu item with menu.add().

The whole method should now look like this:

@Overridepublic boolean onCreateOptionsMenu(Menu menu) {

boolean result = super.onCreateOptionsMenu(menu);menu.add(0, INSERT_ID, 0, R.string.menu_insert);

return result;} The arguments passed to add() indicate: a group identifier for this menu (none, in thiscase), a unique ID (defined above), the order of the item (zero indicates no preference), andthe resource of the string to use for the item.

Step 10


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Step 10

Fill out the body of the onOptionsItemSelected() method: This is going to handle our new "Add Note" menu item. When this is selected, the

onOptionsItemSelected() method will be called with the item.getId() set to INSERT_ID (theconstant we used to identify the menu item). We can detect this, and take the appropriateactions:

The super.onOptionsItemSelected(item) method call goes at the end of this method wewant to catch our events first!

Write a switch statement on item.getItemId(). In the case ofINSERT_ID, call a new method,

createNote(), and return true, because we have handled this event and do not want topropagate it through the system.

Return the result of the superclass' onOptionsItemSelected() method at the end.

The whole onOptionsItemSelect() method should now look like this:

@Overridepublic boolean onOptionsItemSelected(MenuItem item) {

switch (item.getItemId()) {case INSERT_ID:

createNote();return true;}

return super.onOptionsItemSelected(item);}

Step 11


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Step 11

Add a new createNote() method: In this first version of our application, createNote() is not going to be

very useful. We will simply create a new note with a title assigned to itbased on a counter ("Note 1", "Note 2"...) and with an empty body. Atpresent we have no way of editing the contents of a note, so for now wewill have to be content making one with some default values:

Construct the name using "Note" and the counter we defined in theclass: String noteName = "Note " + mNoteNumber++

Call mDbHelper.createNote() using noteName as the title and "" for thebody

Call fillData() to populate the list of notes (inefficient but simple) we'llcreate this method next.

The whole createNote() method should look like this:

private void createNote() {String noteName = "Note " + mNoteNumber++;mDbHelper.createNote(noteName, "");fillData();

}

Step 12a


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Step 12a

Define the fillData() method: This method uses SimpleCursorAdapter, which takes a

database Cursor and binds it to fields provided in the layout.These fields define the row elements of our list (in this casewe use the text1 field in our notes_row.xml layout), so this

allows us to easily populate the list with entries from ourdatabase.

To do this we have to provide a mapping from the title field inthe returned Cursor, to our text1 TextView, which is done bydefining two arrays: the first a string array with the list of

columns to mapfrom (just "title" in this case, from theconstant NotesDbAdapter.KEY_TITLE) and, the second, an intarray containing references to the views that we'll bind thedata into (the R.id.text1 TextView).

Step 12b


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Step 12b

This is a bigger chunk of code, so let's first take a look at it: private void fillData() {

// Get all of the notes from the database and create the item listCursor c = mDbHelper.fetchAllNotes();startManagingCursor(c);

String[] from = new String[] { NotesDbAdapter.KEY_TITLE };int[] to = new int[] { R.id.text1 };

// Now create an array adapter and set it to display using ourrow

SimpleCursorAdapter notes =new SimpleCursorAdapter(this, R.layout.notes_row, c, from,

to); setListAdapter(notes);}

Step 12c


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Step 12c

Here's what we've done: After obtaining the Cursor from mDbHelper.fetchAllNotes(), we use an Activity method

called startManagingCursor() that allows Android to take care of the Cursor lifecycle insteadof us needing to worry about it. (We will cover the implications of the lifecycle in exercise 3,but for now just know that this allows Android to do some of our resource managementwork for us.)

Then we create a string array in which we declare the column(s) we want (just the title, inthis case), and an int array that defines the View(s) to which we'd like to bind the columns(these should be in order, respective to the string array, but here we only have one for

each). Next is the SimpleCursorAdapter instantiation. Like many classes in Android, the

SimpleCursorAdapter needs a Context in order to do its work, so we pass in this for thecontext (since subclasses of Activity implement Context). We pass the notes_row View wecreated as the receptacle for the data, the Cursor we just created, and then our arrays.

In the future, remember that the mapping between the from columns and to resources isdone using the respective ordering of the two arrays. If we had more columns we wantedto bind, and more Views to bind them in to, we would specify them in order, for example

we might use { NotesDbAdapter.KEY_TITLE, NotesDbAdapter.KEY_BODY } and { R.id.text1,R.id.text2 } to bind two fields into the row (and we would also need to define text2 in thenotes_row.xml, for the body text). This is how you can bind multiple fields into a single row(and get a custom row layout as well).

If you get compiler errors about classes not being found, ctrl-shift-O or (cmd-shift-O on themac) to organize imports.

Step 13


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Step 13

Run it! Right click on the Notepadv1 project.

From the popup menu, select Run As > Android Application.

If you see a dialog come up, select Android Launcher as the

way of running the application (you can also use the link nearthe top of the dialog to set this as your default for the

workspace; this is recommended as it will stop the plugin from

asking you this every time).

Add new notes by hitting the menu button and selectingAdd

Item from the menu.

Project 5: Notepad 2


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Project 5: Notepad 2

In this exercise, you will add a second Activity to your notepadapplication, to let the user create and edit notes. You will also

allow the user to delete existing notes through a context

menu. The new Activity assumes responsibility for creating

new notes by collecting user input and packing it into a return

Bundle provided by the intent. This exercise demonstrates:

Constructing a new Activity and adding it to the Android manifest

Invoking another Activity asynchronously using

startActivityForResult()

Passing data between Activity in Bundle objects How to use a more advanced screen layout

How to create a context menu

Step 1


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Step 1

Create a new Android project using the sources from Notepadv2 under theNotepadCodeLab folder, just like you did for the first exercise. If you see an errorabout AndroidManifest.xml, or some problems related to an android.zip file,right click on the project and select Android Tools > Fix Project Properties.

Open the Notepadv2 project and take a look around:

Open and look at the strings.xml file under res/values there are several newstrings which we will use for our new functionality

Also, open and take a look at the top of the Notepadv2 class, you will noticeseveral new constants have been defined along with a new mNotesCursor fieldused to hold the cursor we are using.

Note also that the fillData() method has a few more comments and now uses thenew field to store the notes Cursor. The onCreate() method is unchanged fromthe first exercise. Also notice that the member field used to store the notesCursor is now called mNotesCursor. The m denotes a member field and is part ofthe Android coding style standards.

There are also a couple of new overridden methods (onCreateContextMenu(),onContextItemSelected(), onListItemClick() and onActivityResult()) which we willbe filling in below.

Step 2a


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Step 2a

First, let's create the context menu that will allow users todelete individual notes. Open the Notepadv2 class.

In order for each list item in the ListView to register for the

context menu, we call registerForContextMenu() and pass it

our ListView. So, at the very end of the onCreate() method add

this line:

registerForContextMenu(getListView());

Because our Activity extends the ListActivity class,

getListView() will return us the local ListView object for the

Activity. Now, each list item in this ListView will activate thecontext menu.

Step 2b


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Step 2b

Now fill in the onCreateContextMenu() method. This callback issimilar to the other menu callback used for the options menu. Here,we add just one line, which will add a menu item to delete a note.Call menu.add() like so:

public void onCreateContextMenu(Menu menu, View v,ContextMenu.ContextMenuInfo menuInfo) {

super.onCreateContextMenu(menu, v, menuInfo);menu.add(0, DELETE_ID, 0, R.string.menu_delete);

}

The onCreateContextMenu() callback passes some otherinformation in addition to the Menu object, such as the View thathas been triggered for the menu and an extra object that may

contain additional information about the object selected. However,we don't care about these here, because we only have one kind ofobject in the Activity that uses context menus. In the next step, we'llhandle the menu item selection.

Step 3


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Step 3

Now that the we've registered our ListView for a context menu anddefined our context menu item, we need to handle the callback when itis selected. For this, we need to identify the list ID of the selected item,then delete it. So fill in the onContextItemSelected() method like this: public boolean onContextItemSelected(MenuItem item) {

switch(item.getItemId()) {case DELETE_ID:

AdapterContextMenuInfo info = (AdapterContextMenuInfo)item.getMenuInfo();mDbHelper.deleteNote(info.id);fillData();return true;

}return super.onContextItemSelected(item);

}

Here, we retrieve the AdapterContextMenuInfo with getMenuInfo().The idfield of this object tells us the position of the item in the ListView.We then pass this to the deleteNote() method of our NotesDbAdapterand the note is deleted. That's it for the context menu notes can nowbe deleted.

Step 4a
http://developer.android.com/reference/android/widget/AdapterView.AdapterContextMenuInfo.htmlhttp://developer.android.com/reference/android/view/MenuItem.htmlhttp://developer.android.com/reference/android/view/MenuItem.htmlhttp://developer.android.com/reference/android/widget/AdapterView.AdapterContextMenuInfo.html


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Step 4a

Fill in the body of the createNote() method: Create a new Intent to create a note (ACTIVITY_CREATE) using

the NoteEdit class. Then fire the Intent using the

startActivityForResult() method call:

Intent i = new Intent(this, NoteEdit.class);

startActivityForResult(i, ACTIVITY_CREATE);

This form of the Intent call targets a specific class in our

Activity, in this case NoteEdit. Since the Intent class will need

to communicate with the Android operating system to route

requests, we also have to provide a Context (this).

Step 4b


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Step 4b

The startActivityForResult() method fires the Intent in a waythat causes a method in our Activity to be called when the

new Activity is completed. The method in our Activity that

receives the callback is called onActivityResult() and we will

implement it in a later step. The other way to call an Activity is

using startActivity() but this is a "fire-and-forget" way ofcalling it in this manner, our Activity is not informed when

the Activity is completed, and there is no way to return result

information from the called Activity with startActivity().

Don't worry about the fact that NoteEdit doesn't exist yet, wewill fix that soon.

Step 5a


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Step 5a

Fill in the body of the onListItemClick() override. onListItemClick() is a callback method that we'll override. It is

called when the user selects an item from the list. It is passed

four parameters: the ListView object it was invoked from, the

View inside the ListView that was clicked on, the position in

the list that was clicked, and the mRowId of the item that was

clicked. In this instance we can ignore the first two parameters

(we only have one ListView it could be), and we ignore the

mRowId as well. All we are interested in is the position that

the user selected. We use this to get the data from the correct

row, and bundle it up to send to the NoteEdit Activity.

Step 5b


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Step 5b

In our implementation of the callback, the method creates an Intentto edit the note using the NoteEdit class. It then adds data into theextras Bundle of the Intent, which will be passed to the calledActivity. We use it to pass in the title and body text, and the mRowIdfor the note we are editing. Finally, it will fire the Intent using thestartActivityForResult() method call. Here's the code that belongs in

onListItemClick(): super.onListItemClick(l, v, position, id);

Cursor c = mNotesCursor;c.moveToPosition(position);Intent i = new Intent(this, NoteEdit.class);i.putExtra(NotesDbAdapter.KEY_ROWID, id);

i.putExtra(NotesDbAdapter.KEY_TITLE, c.getString(c.getColumnIndexOrThrow(NotesDbAdapter.KEY_TITLE)));

i.putExtra(NotesDbAdapter.KEY_BODY, c.getString(c.getColumnIndexOrThrow(NotesDbAdapter.KEY_BODY)));

startActivityForResult(i, ACTIVITY_EDIT);

Step 5c


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Step 5c

putExtra() is the method to add items into the extras Bundleto pass in to intent invocations. Here, we are using the Bundle

to pass in the title, body and mRowId of the note we want to

edit.

The details of the note are pulled out from our query Cursor,

which we move to the proper position for the element that

was selected in the list, with the moveToPosition() method.

With the extras added to the Intent, we invoke the Intent on

the NoteEdit class by passing startActivityForResult() the

Intent and the request code. (The request code will bereturned to onActivityResult as the requestCode parameter.)

Step 6a


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Step 6a

The above createNote() and onListItemClick() methods use anasynchronous Intent invocation. We need a handler for the callback, sohere we fill in the body of the onActivityResult().

onActivityResult() is the overridden method which will be called whenan Activity returns with a result. (Remember, an Activity will only returna result if launched with startActivityForResult.) The parametersprovided to the callback are:

requestCode the original request code specified in the Intentinvocation (either ACTIVITY_CREATE or ACTIVITY_EDIT for us).

resultCode the result (or error code) of the call, this should be zero ifeverything was OK, but may have a non-zero code indicating thatsomething failed. There are standard result codes available, and you canalso create your own constants to indicate specific problems.

intent this is an Intent created by the Activity returning results. It canbe used to return data in the Intent "extras."

The combination of startActivityForResult() and onActivityResult() canbe thought of as an asynchronous RPC (remote procedure call) andforms the recommended way for an Activity to invoke another andshare services.

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Step 6b

Here's the code that belongs in your onActivityResult(): super.onActivityResult(requestCode, resultCode, intent);

Bundle extras = intent.getExtras();

switch(requestCode) {case ACTIVITY_CREATE:

String title = extras.getString(NotesDbAdapter.KEY_TITLE);String body = extras.getString(NotesDbAdapter.KEY_BODY);

mDbHelper.createNote(title, body);fillData();break;

case ACTIVITY_EDIT:Long mRowId = extras.getLong(NotesDbAdapter.KEY_ROWID);if (mRowId != null) {

String editTitle = extras.getString(NotesDbAdapter.KEY_TITLE);String editBody = extras.getString(NotesDbAdapter.KEY_BODY);mDbHelper.updateNote(mRowId, editTitle, editBody);

}fillData();break;

}

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Step 6c

We are handling both the ACTIVITY_CREATE andACTIVITY_EDIT activity results in this method.

In the case of a create, we pull the title and body from the

extras (retrieved from the returned Intent) and use them to

create a new note.

In the case of an edit, we pull the mRowId as well, and use

that to update the note in the database.

fillData() at the end ensures everything is up to date .

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Step 7a

Open the file note_edit.xml that has been provided and take a lookat it. This is the UI code for the Note Editor.

This is the most sophisticated UI we have dealt with yet. The file isgiven to you to avoid problems that may sneak in when typing thecode. (The XML is very strict about case sensitivity and structure,mistakes in these are the usual cause of problems with layout.)

There is a new parameter used here that we haven't seen before:android:layout_weight (in this case set to use the value 1 in eachcase).

layout_weight is used in LinearLayouts to assign "importance" toViews within the layout. All Views have a default layout_weight ofzero, meaning they take up only as much room on the screen as theyneed to be displayed. Assigning a value higher than zero will split up

the rest of the available space in the parent View, according to thevalue of each View's layout_weight and its ratio to the overalllayout_weight specified in the current layout for this and other Viewelements.

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Step 7b

To give an example: let's say we have a text label and two text editelements in a horizontal row. The label has no layout_weight

specified, so it takes up the minimum space required to render. If

the layout_weight of each of the two text edit elements is set to 1,

the remaining width in the parent layout will be split equally

between them (because we claim they are equally important). If thefirst one has a layout_weight of 1 and the second has a

layout_weight of 2, then one third of the remaining space will be

given to the first, and two thirds to the second (because we claim

the second one is more important).

This layout also demonstrates how to nest multiple layouts inside

each other to achieve a more complex and pleasant layout. In this

example, a horizontal linear layout is nested inside the vertical one

to allow the title label and text field to be alongside each other,

horizontally.

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Step 8

Create a NoteEdit class that extends android.app.Activity. This is the first time we will have created an Activity without the

Android Eclipse plugin doing it for us. When you do so, the onCreate()method is not automatically overridden for you. It is hard to imagine anActivity that doesn't override the onCreate() method, so this should bethe first thing you do.

Right click on the com.android.demo.notepad2 package in the Package

Explorer, and select New > Class from the popup menu. Fill in NoteEdit for the Name: field in the dialog.

In the Superclass: field, enter android.app.Activity (you can also justtype Activity and hit Ctrl-Space on Windows and Linux or Cmd-Space onthe Mac, to invoke code assist and find the right package and class).

Click Finish.

In the resulting NoteEdit class, right click in the editor window andselect Source > Override/Implement Methods...

Scroll down through the checklist in the dialog until you seeonCreate(Bundle) and check the box next to it.

Click OK.The method should now appear in your class.

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Step 9a

Fill in the body of the onCreate() method for NoteEdit. This will set the title of our new Activity to say "Edit Note" (one of

the strings defined in strings.xml). It will also set the content view touse our note_edit.xml layout file. We can then grab handles to thetitle and body text edit views, and the confirm button, so that ourclass can use them to set and get the note title and body, and attachan event to the confirm button for when it is pressed by the user.

We can then unbundle the values that were passed in to the Activitywith the extras Bundle attached to the calling Intent. We'll use themto pre-populate the title and body text edit views so that the usercan edit them. Then we will grab and store the mRowId so we cankeep track of what note the user is editing.

Inside onCreate(), set up the layout: setContentView(R.layout.note_edit);

Change the Activity title to the "Edit Note" string:

setTitle(R.string.edit_note);

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Step 9b

Find the EditText and Button components we need: These arefound by the IDs associated to them in the R class, and need

to be cast to the right type of View (EditText for the two text

views, and Button for the confirm button):

mTitleText = (EditText) findViewById(R.id.title);

mBodyText = (EditText) findViewById(R.id.body);

Button confirmButton = (Button) findViewById(R.id.confirm);

Note that mTitleText and mBodyText are member fields (you

need to declare them at the top of the class definition).

At the top of the class, declare a Long mRowId private field tostore the current mRowId being edited (if any).

Step 9c
http://developer.android.com/reference/android/widget/EditText.htmlhttp://developer.android.com/reference/android/widget/Button.htmlhttp://developer.android.com/reference/android/widget/Button.htmlhttp://developer.android.com/reference/android/widget/EditText.html


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Step 9c

Continuing inside onCreate(), add code to initialize the title, body andmRowId from the extras Bundle in the Intent (if it is present): mRowId = null;

Bundle extras = getIntent().getExtras();if (extras != null) {

String title = extras.getString(NotesDbAdapter.KEY_TITLE);String body = extras.getString(NotesDbAdapter.KEY_BODY);mRowId = extras.getLong(NotesDbAdapter.KEY_ROWID);

if (title != null) {mTitleText.setText(title);

}if (body != null) {

mBodyText.setText(body);}

}

We are pulling the title and body out of the extras Bundle that was setfrom the Intent invocation.

We also null-protect the text field setting (i.e., we don't want to set thetext fields to null accidentally).

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Step 9d

Create an onClickListener() for the button: Listeners can be one of themore confusing aspects of UI implementation, but what we are trying toachieve in this case is simple. We want an onClick() method to be calledwhen the user presses the confirm button, and use that to do somework and return the values of the edited note to the Intent caller. We dothis using something called an anonymous inner class. This is a bitconfusing to look at unless you have seen them before, but all you really

need to take away from this is that you can refer to this code in thefuture to see how to create a listener and attach it to a button.(Listeners are a common idiom in Java development, particularly foruser interfaces.) Here's the empty listener:

confirmButton.setOnClickListener(new View.OnClickListener() {

public void onClick(View view) {

}

});

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p

Fill in the body of the onClick() method of the OnClickListener created inthe last step.

This is the code that will be run when the user clicks on the confirmbutton. We want this to grab the title and body text from the edit textfields, and put them into the return Bundle so that they can be passedback to the Activity that invoked this NoteEdit Activity. If the operationis an edit rather than a create, we also want to put the mRowId into the

Bundle so that the Notepadv2 class can save the changes back to thecorrect note.

Create a Bundle and put the title and body text into it using theconstants defined in Notepadv2 as keys: Bundle bundle = new Bundle();

bundle.putString(NotesDbAdapter.KEY_TITLE, mTitleText.getText().toString());

bundle.putS

Documents

Chris Rider and Eric Rolf - Introduction to Android