Android Activity Class boilerplate code

1. An dummy activity layout, activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android=""

2. The dummy activity class,

public class MainActivity extends Activity {

    protected void onCreate(Bundle savedInstanceState) {
        Log.i(this.getLocalClassName(),"Activity created.");

    protected void onRestart() {
        Log.i(this.getLocalClassName(), "Activity restarted.");

    protected void onStart() {
        Log.i(this.getLocalClassName(), "Activity started.");

    protected void onResume() {
        Log.i(this.getLocalClassName(), "Activity resumed.");

    protected void onPause() {
        Log.i(this.getLocalClassName(), "Activity paused.");

    protected void onStop() {
        Log.i(this.getLocalClassName(), "Activity stopped.");

    protected void onDestroy() {
        Log.i(this.getLocalClassName(), "Activity destroyed.");

    protected void onRestoreInstanceState(Bundle savedInstanceState) {
        Log.i(this.getLocalClassName(), "Restore instance.");

    protected void onSaveInstanceState(Bundle outState) {
        Log.i(this.getLocalClassName(), "Save instance.");


3. Register the MainActivity in the application manifest file.

<activity android:name="com.example.MainActivity"/>

onCreate() is the only method required to have for creating the simplest activity. It is called when the activity is starting. This is where most initialization should go: calling setContentView(int) to inflate the activity’s UI, using findViewById(int) to programmatically interact with widgets in the UI, calling managedQuery(, String[], String, String[], String) to retrieve cursors for data being displayed, etc.

You can call finish() from within this function, in which case onDestroy() will be immediately called without any of the rest of the activity lifecycle (onStart(), onResume(), onPause(), etc) executing.

Derived classes must call through to the super class’s implementation of this method. If they do not, an exception will be thrown.

The parameter savedInstanceState: If the activity is being re-initialized after previously being shut down then this Bundle contains the data it most recently supplied in onSaveInstanceState(Bundle). Otherwise it is null.

onRestart() is called after onStop() when the current activity is being re-displayed to the user (the user has navigated back to it). It will be followed by onStart() and then onResume().

For activities that are using raw Cursor objects (instead of creating them through managedQuery(, String[], String, String[], String), this is usually the place where the cursor should be requeried (because you had deactivated it in onStop().

Derived classes must call through to the super class’s implementation of this method. If they do not, an exception will be thrown.

onStart() is called after onCreate(Bundle) — or after onRestart() when the activity had been stopped, but is now again being displayed to the user. It will be followed by onResume().

Derived classes must call through to the super class’s implementation of this method. If they do not, an exception will be thrown.

onResume() is called after onRestoreInstanceState(Bundle), onRestart(), or onPause() for your activity to start interacting with the user. This is a good place to begin animations, open exclusive-access devices (such as the camera), etc.

Keep in mind that onResume is not the best indicator that your activity is visible to the user; a system window such as the keyboard may be in front. Use onWindowFocusChanged(boolean) to know for certain that your activity is visible to the user (for example, to resume a game).

Derived classes must call through to the super class’s implementation of this method. If they do not, an exception will be thrown.

onPause() is called as part of the activity lifecycle when an activity is going into the background, but has not (yet) been killed. The counterpart to onResume().

When activity B is launched in front of activity A, this callback will be invoked on A. B will not be created until A’s onPause() returns, so be sure to not do anything lengthy here.

This callback is mostly used for saving any persistent state the activity is editing, to present a “edit in place” model to the user and making sure nothing is lost if there are not enough resources to start the new activity without first killing this one. This is also a good place to do things like stop animations and other things that consume a noticeable amount of CPU in order to make the switch to the next activity as fast as possible, or to close resources that are exclusive access such as the camera.

In situations where the system needs more memory it may kill paused processes to reclaim resources. Because of this, you should be sure that all of your state is saved by the time you return from this function. In general onSaveInstanceState(Bundle) is used to save per-instance state in the activity and this method is used to store global persistent data (in content providers, files, etc.)

After receiving this call you will usually receive a following call to onStop() (after the next activity has been resumed and displayed), however in some cases there will be a direct call back to onResume() without going through the stopped state.

Derived classes must call through to the super class’s implementation of this method. If they do not, an exception will be thrown.

onStop() is called when you are no longer visible to the user. You will next receive either onRestart(), onDestroy(), or nothing, depending on later user activity.

Note that this method may never be called, in low memory situations where the system does not have enough memory to keep your activity’s process running after its onPause() method is called.

Derived classes must call through to the super class’s implementation of this method. If they do not, an exception will be thrown.

onDestroy() is called when the activity is finishing by the finish() call or being destroyed by the android system for saving and restoring system resources. This is the place to perform any final cleanup before an activity is destroyed.

Note: do not count on this method being called as a place for saving data! For example, if an activity is editing data in a content provider, those edits should be committed in either onPause() or onSaveInstanceState(Bundle), not here. This method is usually implemented to free resources like threads that are associated with an activity, so that a destroyed activity does not leave such things around while the rest of its application is still running. There are situations where the system will simply kill the activity’s hosting process without calling this method (or any others) in it, so it should not be used to do things that are intended to remain around after the process goes away.

Derived classes must call through to the super class’s implementation of this method. If they do not, an exception will be thrown.

onSaveInstanceState (Bundle outState) is called to retrieve per-instance state from an activity before being killed so that the state can be restored in onCreate(Bundle) or onRestoreInstanceState(Bundle) (the Bundle populated by this method will be passed to both).

This method is called before an activity may be killed so that when it comes back some time in the future it can restore its state. For example, if activity B is launched in front of activity A, and at some point activity A is killed to reclaim resources, activity A will have a chance to save the current state of its user interface via this method so that when the user returns to activity A, the state of the user interface can be restored via onCreate(Bundle) or onRestoreInstanceState(Bundle).

Do not confuse this method with activity lifecycle callbacks such as onPause(), which is always called when an activity is being placed in the background or on its way to destruction, or onStop() which is called before destruction. One example of when onPause() and onStop() is called and not this method is when a user navigates back from activity B to activity A: there is no need to call onSaveInstanceState(Bundle) on B because that particular instance will never be restored, so the system avoids calling it. An example when onPause() is called and not onSaveInstanceState(Bundle) is when activity B is launched in front of activity A: the system may avoid calling onSaveInstanceState(Bundle) on activity A if it isn’t killed during the lifetime of B since the state of the user interface of A will stay intact.

The default implementation takes care of most of the UI per-instance state for you by calling onSaveInstanceState() on each view in the hierarchy that has an id, and by saving the id of the currently focused view (all of which is restored by the default implementation of onRestoreInstanceState(Bundle)). If you override this method to save additional information not captured by each individual view, you will likely want to call through to the default implementation, otherwise be prepared to save all of the state of each view yourself.

If called, this method will occur before onStop(). There are no guarantees about whether it will occur before or after onPause().

onRestoreInstanceState (Bundle savedInstanceState) is called after onStart() when the activity is being re-initialized from a previously saved state, given here in savedInstanceState. Most implementations will simply use onCreate(Bundle) to restore their state, but it is sometimes convenient to do it here after all of the initialization has been done or to allow subclasses to decide whether to use your default implementation. The default implementation of this method performs a restore of any view state that had previously been frozen by onSaveInstanceState(Bundle).

This method is called between onStart() and onPostCreate(Bundle).

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