Android: Make use of Android Application Class as Singleton Object

Extending Android Application class is helpful when you would like to store session data or application wise global data.
In any android application, there will be only one application object, so you should you it as Singleton

MyAppApplication.java #29:
I called a method onAppCreated() and its an abstract method, that’s why i had to make the whole MyAppApplication as an abstract class
Reason:
the onAppCreated is particularly helpful when you will use library projects
For example, you would like to create an app with two versions liteand pro
Obviously there will be a lot of common features and pro version will have some additional features
so you are planning to make a library project named: CoreProject in android and make two sub classes named: appLite and appPro
Now suppose, you would like to know in your appLite that library project CoreProject is created successfully and then call a method
you can then easily implement onAppCreated() method in subclass appLite

MyAppApplication.java #32:
in initializeInstance(), you can do your app’s version wise specialized task
or may be something that you need to be done before the creation of your first activity

I have created and called screenConfiguration() method, which is used for determining the size of ScreenWidth and ScreenHeight
and it also helpful if you like to know the device is a tab or phone

MyAppApplication.java #67:
You may need to know if the app runs for the first time. suppose, you get to show the user the EULA (End User License Agreement) page for the first time.
In this case you can save the value in preferences and when the app get started you can call isFirstRun() to know if it is first time,
after that call setRunned() method, which will set the value false

MyAppApplication.java #80:
in onTerminate() method do your application wise clean up task
suppose, on close application you need to clear the user session data

display.getSize() is added and
display.getWidth(); display.getHeight();
are deprecated on API version 13

@TargetApi(Build.VERSION_CODES.HONEYCOMB_MR2)
prevents the compilation error where minSdkVersion < 13

Application Class example

 package com.example; import android.annotation.TargetApi; import android.app.Application; import android.content.Context; import android.content.res.Configuration; import android.graphics.Point; import android.os.Build; import android.view.Display; import android.view.WindowManager; public abstract class MyAppApplication extends Application { private static MyAppApplication sInstance;	SharedPreferences mPref; public static MyAppApplication getInstance() { return sInstance; } @Override public void onCreate() { super.onCreate(); sInstance = this; sInstance.initializeInstance(); onAppCreated(); } private void initializeInstance() { // Do your application wise initialization task screenConfiguration();	// set application wise preference	mPref = this.getApplicationContext().getSharedPreferences("pref_key", MODE_PRIVATE); } // particularly applicable in library projects public abstract void onAppCreated(); @TargetApi(Build.VERSION_CODES.HONEYCOMB_MR2) public void screenConfiguration() { Configuration config = getResources().getConfiguration(); boolean isTab = (config.screenLayout & Configuration.SCREENLAYOUT_SIZE_MASK) >= Configuration.SCREENLAYOUT_SIZE_LARGE; Point size = new Point(); WindowManager wm = (WindowManager) this.getSystemService(Context.WINDOW_SERVICE); Display display = wm.getDefaultDisplay(); int deviceScreenWidth; int deviceScreenHeight; try { display.getSize(size); deviceScreenWidth = size.x; deviceScreenHeight = size.y; } catch (NoSuchMethodError e) { deviceScreenWidth = display.getWidth(); deviceScreenHeight = display.getHeight(); } }	public boolean isFirstRun() {	// return true if the app is running for the first time return mPref.getBoolean("is_first_run", true); } public void setRunned() {	// after a successful run, call this method to set first run false SharedPreferences.Editor edit = mPref.edit(); edit.putBoolean("is_first_run", false); edit.commit(); } @Override public void onTerminate() { // Do your application wise Termination task super.onTerminate(); } } 

Here is a sample application tag from AndroidManifest file

AndroidManifest.xml

 <application android:name="com.example.MyAppApplication" android:allowBackup="true" android:icon="@drawable/apps_logo" <!-- application logo --> android:logo="@drawable/action_bar_logo" <!-- action bar home logo --> android:label="@string/app_name" android:theme="@style/Theme.app_theme"> <!-- other manifest elements goes here... --> </application>