What methods are invoked in the Activity Lifecycle

问题:

Let's say I have a Hello World single Activity application. I start this application.

What methods are invoked in each case:

• Home button is pressed: ?
  Back button is pressed: ?
  Phone call is received: ?

What methods are invoked once the user starts the application again via the app icon (assuming the OS hasn't had a "other apps need memory condition"):

• Home button was pressed: ?
  Back button was pressed: ?
  Phone call was received: ?

Thanks all.

Edit: Extra Credit: How can the user invoke onPause without invoking onStop?

回答1:

both pressing home button and receiving a call don't remove the activity from the task's stack, and will be available when you re-enter the app => onPause() => onStop().

as the activity lifecycle diagram shows, re-entering the app calls => onRestart() => onStart() => onResume()

pressing the back button instead kills the activity => onPause() => onStop() => onDestroy()

re-entering the app in this case calls the classics => onCreate() => onStart() => onResume()

EDIT

from http://developer.android.com/reference/android/app/Activity.html#ActivityLifecycle

If an activity has lost focus but is still visible (that is, a new non-full-sized or transparent activity has focus on top of your activity), it is paused. A paused activity is completely alive (it maintains all state and member information and remains attached to the window manager), but can be killed by the system in extreme low memory situations.

回答2:

For understand ACTIVITY LIFECYCLE i create the demo See HERE

And different case study i added.

MainActivity.java

    public class MainActivity extends AppCompatActivity {

    private static final String TAG = "State changed";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Log.i(TAG, "onCreate: ");
    }

    public void OpenDialog(View view) {

        final AlertDialog alertDialog = new AlertDialog.Builder(MainActivity.this).create(); //Read Update
        alertDialog.setTitle("hi");
        alertDialog.setMessage("this is my app");

        alertDialog.setButton("Continue..", new DialogInterface.OnClickListener() {
            public void onClick(DialogInterface dialog, int which) {
                // here you can add functions
                alertDialog.dismiss();
            }
        });

        alertDialog.show();  //<-- Show dialog
    }

    @Override
    protected void onStart() {
        super.onStart();
        Log.i(TAG, "onStart: " );
    }

    @Override
    protected void onResume() {
        super.onResume();

        Log.i(TAG, "onResume: ");

    }

    @Override
    protected void onPause() {
        super.onPause();

        Log.i(TAG, "onPause: ");
    }

    @Override
    protected void onStop() {
        super.onStop();
        Log.i(TAG, "onStop: ");
    }

    @Override
    protected void onRestart() {
        super.onRestart();
        Log.i(TAG, "onRestart: ");
    }

    @Override
    public void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
        Log.i(TAG, "onSaveInstanceState: ");
    }

    @Override
    protected void onRestoreInstanceState(Bundle savedInstanceState) {
        super.onRestoreInstanceState(savedInstanceState);
        Log.i(TAG, "onRestoreInstanceState: ");
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        Log.i(TAG, "onDestroy: ");
    }

    @Override
    public void onBackPressed() {
        super.onBackPressed();
        Log.i(TAG, "onBackPressed: ");
    }

}

Case Study

Case 1 = First click the app icon

Note : here does not show the onRestoreInstanceState because it execute on runtime

I/State changed: onCreate:

I/State changed: onStart:

I/State changed: onResume:

Case 2 = Click Home Button (same happended when screen light off or coming call)

I/State changed: onPause:

I/State changed: onSaveInstanceState:

I/State changed: onStop:

Case 3 = (case 2 continue) Open App via Recent

I/State changed: onRestart:

I/State changed: onStart:

I/State changed: onResume:

Case 4 = Click Back button (onBackPressed method call)

I/State changed: onPause:

I/State changed: onStop:

I/State changed: onDestroy:

Case 5 = Configration Change (Rotate the screen)

I/State changed: onPause:

I/State changed: onSaveInstanceState:

I/State changed: onStop:

I/State changed: onDestroy:

I/State changed: onCreate:

I/State changed: onStart:

I/State changed: onRestoreInstanceState:

I/State changed: onResume:

回答3:

Well see, while a sequence of events may occur with your hello world program, the same sequence may not occur in say a video game, because Android will probably Destroy it for taking up too much resources.

The best way I have found to see the lifecycle for my app is to override all the methods (onStart, onRestart,..., including the onSaveInstance and onRestoreInstance) and insert log statements in each one. Like so:

@Override
public void onDestroy() {
    // Call the super class 
    super.onDestroy();
    // Log the action
    Log.d("Debug", "onDestroy() has been called!");
}

Now I can go to logcat and see what events took place.

回答4:

There can be several scenarios

1. Opening the app from the app icon. following methods are called

   onCreate()-->onStart()-->onResume()

2. When user presses the home button

   onPause()-->onStop()

3. When user returns to the app from the Activity Stack

   onRestart()-->onStart()--> onResume()

4. When the app is running and user presses the power button

   onPause()-->onStop()

5. When user unlocks the phone

   onRestart()-->onStart()--> onResume()

6. When user gets an incoming call while you are in the app

   onPause()

7. When user returns to the app after disconnecting the phone call

   onResume()

8. When user presses the back button from the app

   onPause()-->onStop()-->onDestroy()

9. And when the user presses the home button and from the activity stack user swipes the app.onDestroy() method may or may not be called depending upon the OS contains the context of the Activity or not according to memory requirements