Salt march 2011-building twitter app

Building Twitter App

Rohit Ghatol

About MeRohit Ghatol

1. Architect @QuickOffice2. Project Mgr @Synerzip3. Certified Scrum Master4. Author “Beginning PhoneGap” @Apress5. Founder TechNext Pune (Pune Developer

Community)

LinkedIn ProfileLinkedIn Profile

Topics – Part 1

• Twitter App Demo• Twitter RestFul API & Java Library• Twitter OAuth• Coding the List Activity• Understanding AsyncTask• Issue with Icons in ListView

3

Topics – Part 2

• Coding different Types of Services• Coding Alarm & Notification Manager• Coding Broadcast Receiver• Coding SQLite DB• Drawbacks of Twitter App• C2DM to Rescue• Understanding C2DM and short Demo

4

Building Twitter App – Part 1

5

Twitter App Demo

http://code.google.com/p/DroidTwitt

Youtube Video Demo

• http://www.youtube.com/user/rohitssghatol#p/u/13/XhCZpxWDtx0

Twitter Requirements

OAuth Authentication

OAuth AuthenticationFetch TweetsFetch Tweets

Send TweetsSend Tweets

Background SyncBackground Sync

Overall Architecture

OAuth Authentication

First Time Launch

Asking Service To Fetch Tweets

Triggering Service every n minutes

Phone Boot Event

Battery Low Event

OAuth

Short Introduction to OAuth

http://fotofast.comhttp://fotofast.com

username

password

LoginLogin CancelCancel

http://fotofast.comhttp://fotofast.comWelcome Rohit

Picasa Flickr

Print PhotoPrint Photo


username

password


Welcome Rohit

Enter Credentials for Picasa

If I go to a restaurant, do I give my ATM Card and Pin to the waiter to pay my bills?

Then Why should I give my Picasa Credentials to fotofast.com?

Take 2, Action


username

password



Picasa Flickr

Print PhotoPrint Photo

http://picasa.comhttp://picasa.com

username

password


Welcome to Picasa

Look Ma its Picasa itself asking for password!

http://picasa.comhttp://picasa.com

Choose Album to Share with FotoFast

Choose Album to Share with FotoFast

11 22

44 55

33

66


Picasa Albums

Choose photo to Print Photo

Choose photo to Print Photo

Look Ma! I am able to print picasa photos from FotoFast

Twitter OAuth in Android

About OAuth

• The way OAuth works for Web is Browser redirects between the 2 sites

• Browser first shows FotoFast, which redirects you to Picasa to authenticate and approve sharing data with FotoFast

• On proper Authentication and Approval, Browser takes you back to FotoFast.com

How does the same work for Android Applications?

Steps of Twitter OAuth

Step 1 : Register with Twitter for OAuth Token

Step 2: Register your Activity to handle url “DroidTwit://twitt”

<activity android:name=".OAuthLogin" android:label="@string/app_name”android:launchMode="singleTask"><intent-filter>

<action android:name="android.intent.action.VIEW"></action><category

android:name="android.intent.category.DEFAULT"></category><category

android:name="android.intent.category.BROWSABLE"></category><data android:scheme="DroidTwit"

android:host="twitt"></data></intent-filter>

</activity>

Step 3: Create a OAuth URL and ask browser to show it

OAuth URL also contains CallBack URL you URL can redirect back to

your activity

public static final String CALLBACK_URL ="DroidTwitt://twitt";

public void buttonClick(){OAuthSignpostClient client = new OAuthSignpostClient

(TWITTER_KEY, TWITTER_SECRET,CALLBACK_URL);

final URI twitterUrl = client.authorizeUrl();

//Start BrowserstartActivity(new Intent(Intent.ACTION_VIEW,

Uri.parse(twitterUrl.toString())));}

Step 4: Handle Response from Browser after OAuth

@Overrideprotected void onNewIntent(final Intent intent) {

super.onNewIntent(intent);final Uri uri = intent.getData();if ((uri != null) && uri.toString().startsWith(CALLBACK_URL)) {

verifier = uri.getQueryParameter("oauth_verifier");client.setAuthorizationCode(verifier);accessTokenAndSecret = client.getAccessToken();Log.e("NewIntent", "Access token: " +

accessTokenAndSecret[0]);Log.e("NewIntent", "Token secret: " +

accessTokenAndSecret[1]);}

}

For more details on OAuth in Android read

http://blog.copyninja.info/2010/09/android-oauth-authentication-with.html

Fetching From Twitter API

Guidelines

• Make the fetch module SynchronousList<Tweets> getLatestTweets();

• Either call directly or through Services

• Use AsyncTask on UI to avoid ANR

ListView Showing Tweets

Lets see a some code for this.

http://code.google.com/p/droidtwit/wiki/AndroidListActivityAsyncTaskTutorial

Need for List Adapter

Entry 1

1

2

3

4

List<Tweet>List<Tweet>

TweetsTweets

Something elseSomething else

Data that can vary

List View functionality is same

Layout can vary

Adapter LayerAdapter Layer

public class MyAdapter extends BaseAdapter{

public int getCount(){ }

public Object getItem(int position){ }

public long getItemId(int position){ }

public View getView(int position,Convert view,..){ }}

List View Explained

Entry 1

Entry 2

Entry 3

Entry 4

1

2

3

4

1 Plank No.

PlankPlank

List View Explained

Entry 1

Entry 2

Entry 3

Entry 4

1

2

3

4

1 Plank No.

Scroll

Entry 5

1

Plank 1 Reused when it pops out the top while scrolling

Thumbnails in ListView

Common Problem and How to solve it

Why is thumbnail is such a problem in ListView?

Entry 1

Entry 2

Entry 3

Entry 4

Thread 1Thread 1

Thread 2Thread 2

Threads to fetch image asynchronously

1

2

3

4

Thread 3Thread 3

Thread 4Thread 4

Why is thumbnail such a problem in ListView?

Entry 5

Entry 6

Entry 7

Entry 8

Thread 1Thread 1Now Thread 1 returns image one and sets it on Plank 1, but Plank 1 should show image from Entry 5.

Wrong images are shown for Entry 5, till Thread 5 returns.

And for each scroll, again images are fetched

1

2

3

4

Thread 5Thread 5

Solution

Entry 1

Entry 2

Entry 3

Entry 4

1

2

3

4Blocking Queue

Thread 1Thread 1

Local Image CacheLocal Image Cache

Thread reads from Blocking Queue, checks the Image Cache, if Image not there, fetches it dumps in Image Cache and gives it to the Image View (If position is valid)

While Scrolling, we add entries in Blocking Queue

Step 0

1

2

3

4Blocking Queue

Thread 1Thread 1


Continuous Thread started

while(true){ PhotoToLoad task = queue.take();

//Fetch photo from internet

//Put photo in cache and set on Image View

}

Thread is blocked on queue.take()

Step 1

…..….. Entry 11

2

3

4

PhotoToLoadPhotoToLoad

Blocking Queue

Thread 1Thread 1


Adapter’s getView() is called

Thread now unblocked





}

Step 1

Entry 11

2

3

4


Blocking Queue

Thread 1Thread 1


Adapter’s getView() is called

Thread now unblocked





}

Step 0

3

4Blocking Queue

Thread 1Thread 1






}

Thread is blocked on queue.take()

Entry 1

Entry 2

1

2

Class Diagram<<ImageLoader>><<ImageLoader>>

void queue(String url, ImageView imageView);

<<ImageCache>><<ImageCache>>

void cache(String url, Bitmap bitmap);

BitMap get(String url);


private String url;private ImageView imageView;

Uses BlockingQueue<PhotoToLoad> and has a thread which keeps running on the

BlockingQueue, to either fetch image from cache or from internet

Complete Example

• The complete example of the QueuedImageLoader can be found http://code.google.com/p/feedreader/source/browse/trunk/FifaLatestNews/src/com/latestnews/cache/QueuedImageLoader.java

Building Twitter App – Part 2

61

Using Services

Lets see Code Demos for this

Complete Detailed Video of this is available on http://code.google.com/p/droidtwit/wiki/AndroidServiceTutorial

Types of Services

• Main Types– Start Service– Bind Service (using Primitives)– Bind Service (using complex types)– Local Service

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Using Alarm Manager

Lets see Code Demo

Listener Battery Event

Lets see Code Demo

SQLite Database Demo

Lets see Code Demo

Pull Vs Server Push

• Twitter App is an example of writing Pull Application

• Pull Applications have some drawbacks

67

Drawbacks of DroidTwitt

Battery Drain

• Application launching every 5/10/15 mins

• Not sure if we will get new information, blindly trying

• Way to optimize is using AlarmManager.setInExactRepeating(), but that only helps so much

Data Usage

• Polling means more use of Data

• If Server is not optimized, then it always sends a chunk of stale data, more bandwidth

• Ways to optimize is ask server to send data on top of what the client already has (say use the timestamp), but that only helps so much

Lag

• Notification using Polling will always have a Lag

• It ends up being a balancing act between Saving Battery and Freshness of the data

Traffic (Server Side)

• Every device, Every n minutes bombarding the Server

• Businesses won’t mind traffic as long it is adding real value. But is this real value?

Load (Server Side)

• Hitting Database blindly when getting traffic

• Servers need to optimized to know whether the polling requests will repeat very n minutes and they only hit database if they have change.

C2DM Players

Google CloudGoogle Cloud

ApplicationServer

ApplicationServer

But Remember a User can have more than one Device!

Android C2DM to Rescue


ApplicationServer

ApplicationServer

Step 1: App Server goes Authentication with Google C2DM Cloud and gets a security token

Security Token

AppServer123


ApplicationServer

ApplicationServer

Step 2: Device 1 Registers itself to Google C2DM Cloud, gets an Registration Id

Security Token

AppServer123


ApplicationServer

ApplicationServer

Step 3: Device 1 tells App Server that its C2DM Reg Id is XYZ

Device Info Reg Id

Rohit’s Phone XYZ

XYZ

Security Token

AppServer123


ApplicationServer

ApplicationServer

Device Info Reg Id

Rohit’s Phone XYZ

Step 4: App Server sends message to C2DM intended for Device with Reg Id XYZ

Security Token

AppServer123


ApplicationServer

ApplicationServer

Device Info Reg Id

Rohit’s Phone XYZ

Step 6: Google C2DM Cloud Service sends Intent to Device with Reg id XYZ

Security Token

AppServer123


ApplicationServer

ApplicationServer

Device Info Reg Id

Rohit’s Phone XYZ

Step 7: Device fetches data from App Server to process

Security Token

AppServer123

C2DM Demo

Lets see the Demo

Q & A

91

More about Me• Twitter - http://twitter.com/#!/rohitghatol • TechGig -

http://www.techgig.com/rohitghatol • LinkedIn -

http://www.linkedin.com/in/rohitghatol• Presentations -

www.slideshare.net/rohitsghatol/ • YouTube Tutorials -

http://www.youtube.com/user/rohitssghatol

Technology

Salt march 2011-building twitter app