CODEWITHSUNDEEP
androidandroid-application-class
The 29th Saltshaker
The 29th Saltshaker

Reputation: 691

Is extending Application how you run code before the launching Activity?

If I do something like this:

public class MyApp extends Application {

    @Override
    public void onCreate() {
        super.onCreate();
        //init something else here if you want
    }

    @Override
    public void onTerminate() {
        super.onTerminate();
        //terminate something else here if you want
    }

}

And include the name of this class in the Manifest file like this:

<application
        android:name="com.packagename.MyApp"
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">

Is this effectively giving us a way to run whatever code we want before and after the app runs?

Edit: If I step into the onCreate() statement I see this in the code:

/**
     * Called when the application is starting, before any activity, service,
     * or receiver objects (excluding content providers) have been created.
     * Implementations should be as quick as possible (for example using 
     * lazy initialization of state) since the time spent in this function
     * directly impacts the performance of starting the first activity,
     * service, or receiver in a process.
     * If you override this method, be sure to call super.onCreate().
     */
    @CallSuper
    public void onCreate() {
    }

    /**
     * This method is for use in emulated process environments.  It will
     * never be called on a production Android device, where processes are
     * removed by simply killing them; no user code (including this callback)
     * is executed when doing so.
     */
    @CallSuper
    public void onTerminate() {
    }

Edit 2: I could also save the application context as a global static variable:

public class MyApp extends Application {
    private static Context context;

    @Override
    public void onCreate() {
        super.onCreate();
        MyApp.context = getApplicationContext();
    }

    public static Context getAppContext() {
        return MyApp.context;
    }

    @Override
    public void onTerminate() {
        super.onTerminate();
    }
}

Upvotes: 3

Views: 1600

Answers (2)

snachmsm
snachmsm

Reputation: 19273

Not before and after but in whole Application lifecycle, e.g. all running Activitys, Services and other contextual creatures... if none of them is currently visible/running Android system may always remove your Application from memory (user also).

If you are looking for a way to run some code outside screen/without any UI, check out Service class or other delayed alarm-basing method.

You can't depend on subclassing Application class because you don't even know when it is killed by OS "automatically".

Upvotes: 2

sumandas
sumandas

Reputation: 565

Yes. The main reason of having it extend Application class

  • Is to have all initialization that you want to be singletons throughout the app and used in components.
  • Have some static variables to be used across components

Ref: Logic why we should use

Upvotes: 1

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