Android Apps Development TrainingDay 4

Android Storage

How do you save your application data ?SharedPreferences*Storage in key-value pairs.

Internal StorageStorage on device memory

External StorageStorage on shared external storage

SQLite Databases*Store structured data in a private database

Network ConnectionsStore data on web

SharedPreferences

The way android stores users preferences

But why SharedPreferences ? Ease of implementation

Faster in terms of coding

Accessibility of key values

Suitable for the small thingse.g. Game difficulty level, user name, user accounts, etc.

I got your back buddy !

SharedPreferences

Every thing is saved in terms of key-valuee.g. NAME, AndroidPhoneNumber, 1234

For the implementation we will be using the:SharedPreferencesGeneral framework to save and retrieve persistent key-value pairs

EditorInterface used for modifying values in a SharedPreferences object

Use of commit() or apply() to make changes persist

Implementation

public class ProjectPreference{SharedPreferences pref;Editor editor;Context _context;int PRIVATE_MODE = 0;private static final String PREF_NAME = prefmyapp;... (A)public ProjectPreference(Context context){this._context = context;pref = _context.getSharedPreferences(PREF_NAME, PRIVATE_MODE);editor = pref.edit();

} ... (B)

Accessing the SharedPreferences thisway gives you more flexibilityWe are creating a separate class here

A: Define Variables

Suppose we have a contact to save:Name

Address

Number

Declare them:public static final String KEY_NAME = name;public static final String KEY_ADD = address;public static final String KEY_NUM = number;

B: Define Getters and Setters

Defining setters and gettersvoid for setterspublic void setName(String key, String value){editor.putString(key, value);editor.commit();

}

for getters public String getName(String key){return pref.getString(key, );

}

You candefine your defaultvalues here

Accessing SharedPreferences

Create an objectProjectPreference SM;

InitializeSM = new ProjectPreference(Class.this);

Access variables and methodsSM.getName(SM.KEY_NAME);

Set valuesSM.setName(SM.KEY_NAME, Android);

Building the application

SQLite Database

SQLite is innate in every Android deviceNo need for extra setup etc.

We only have to define the SQL statements for creating and updating the database

All commands regarding creating tables, inserting values etc. are the same as in SQL

SharedPreferenes
VS
SQLite

SQLite provides capability of more complex storageStorage for large number of data

Higher capabilitiese.g. in the loadshedding app we notice that we do not have to update the app every time a new schedule arrives.

SQLite in Android

Android should use a DBHelperextends SQLiteOpenHelper classTwo main methods:onCreate()Creates the database, parameters needed:DATABASE_NAME

DATABASE_VERSION

onUpgrade()Updates the current database depending upon:DATABASE_VERSION

All operations regarding the database is to be performed by the SQLiteDatabase object

Either the:getWritableDatabase() : Write mode

getReadableDatabase() : Read mode

used with the SQLiteDatabase object. SQLiteDatabase db = this.getWritableDatabase()db.insert(...)

While using the SELECT operations we use the Cursor objectCursor is something similar to an iteratorif(cursor.moveToFirst()){do { } while(cursor.moveToLast())

}

Also during the query we use a rawQuery() method

In insert operations we use the ContentValues object.ContentValues values = new ContentValues( );values.put("name" , "ABC");values.put("phoneNumber" , "123");db.insert(table, null, values);

While programming create the following functions:Getting a single row

Getting all rows

Getting row count

Updating row

Deleting row

For better SQLite implementation

Create both:Data Model classWith all the setters and getters

Data HandlerExtending the SQLiteOpenHelper

Implementing SQLite

Insert userdata intodatabaseRedirect user into another activityshowing the database

AsyncTask

What is threading ?The way any computing device responds to its commands

Android only uses a main thread by default for its application

The main thread processes the following:Application UI

User inputs to the application

Is this enough?

While processing heavy/ time consuming task, the UI will freeze until the task is completeBad practice

For these tasks open a separate threadASYNCTASK

Asynctask is android's multitasker

Methods inside the AsyncTaskOnPreExecute()Generally used to load the progress bar

doInBackground(Params... )All the logic is dumped here

OnProgressUpdate()Called when publishProgress() is called in the doInBackground()

onPostExecute(Result)Gives out the desired result

Using the AsyncTaskExtend the AsyncTaskclass Abc extends AsyncTaskParams: the input, what you pass into the AsyncTask

Progress: on updates, passed to onProgressUpdate()

Result: the output from doInBackground() returned to the onPostExecute()

Call on the AsyncTasknew Abc.execute(Params);