Question

When an activity is created for the first time then system calls the OnContentChanged() method as the first method and last call by system is the OnDetachedFromWindow() method when an activity is killed, but android docs says entire lifetime of an Activity happens between OnCreate() and OnDestroy(). Why? Please help me in understanding difference between these methods.

Code:

import android.app.Activity;
import android.content.res.Configuration;
import android.os.Bundle;
import android.widget.Toast;

public class ActivitylifecycleActivity extends Activity {
    /** Called when the activity is first created. */

    @Override
    public void onContentChanged() {
        super.onContentChanged();   
        Toast.makeText(getApplicationContext(),"1. onContentChanged()", Toast.LENGTH_SHORT).show();
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        Toast.makeText(getApplicationContext(),"2. onCreate()", Toast.LENGTH_SHORT).show();
    }

    @Override
    public void onStart() {
        super.onStart();
        Toast.makeText(getApplicationContext(),"3. onStart()", Toast.LENGTH_SHORT).show();
    }

    @Override
    public void onRestoreInstanceState(Bundle restoreInstanceState) {
        Toast.makeText(getApplicationContext(),"4. onRestoreinstaneState()", Toast.LENGTH_SHORT).show();
        super.onRestoreInstanceState(restoreInstanceState);
    }

    @Override
    public void onRestart() {
        super.onRestart();
        Toast.makeText(getApplicationContext(),"5. onRestart()", Toast.LENGTH_SHORT).show();
    }

    @Override
    protected void onPostCreate(Bundle onpostcrete) {
        super.onPostCreate(onpostcrete);
        Toast.makeText(getApplicationContext(),"6. onPostCreate()", Toast.LENGTH_SHORT).show();
    }

    @Override
    public void onResume() {
        super.onResume();
        Toast.makeText(getApplicationContext(),"7. onResume()", Toast.LENGTH_SHORT).show();
    }

    @Override
    protected void onPostResume() {
        super.onPostResume();
        Toast.makeText(getApplicationContext(),"8. onPostResume()", Toast.LENGTH_SHORT).show();
    }

    @Override
    public void onAttachedToWindow() {
        super.onAttachedToWindow();
        Toast.makeText(getApplicationContext(),"9. onAttachedToWindow()", Toast.LENGTH_SHORT).show();
    }

    @Override
    public void onWindowFocusChanged(boolean bo) {
        super.onWindowFocusChanged(true);
        Toast.makeText(getApplicationContext(),"10. onWindowFocusChanged()", Toast.LENGTH_SHORT).show();
    }

    @Override
    public void onUserLeaveHint() {
        super.onUserLeaveHint();
        Toast.makeText(getApplicationContext(),"11. onUserLeaveHint()", Toast.LENGTH_SHORT).show();
    }

    @Override
    public void onUserInteraction() {
        super.onUserInteraction();
        ii=0;
        Toast.makeText(getApplicationContext(),"12. onUserInteraction()", Toast.LENGTH_SHORT).show();
    }

    @Override
    public void onSaveInstanceState(Bundle savedInstanceState) {
        super.onSaveInstanceState(savedInstanceState);
        Toast.makeText(getApplicationContext(),"13. onSaveInstanceState()", Toast.LENGTH_SHORT).show();
    }

    @Override
    public void onPause() {
        super.onPause();
        Toast.makeText(getApplicationContext(),"14. onPause()", Toast.LENGTH_SHORT).show();
    }

    @Override
    public void onStop() {
        super.onStop();
        Toast.makeText(getApplicationContext(),"15. onStop()", Toast.LENGTH_SHORT).show();
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
        Toast.makeText(getApplicationContext(),"16. onDestroy()", Toast.LENGTH_SHORT).show();
    }

    @Override
    public void onDetachedFromWindow() {
        super.onDetachedFromWindow();
        Toast.makeText(getApplicationContext(),"17. onDetachedFromWindow()", Toast.LENGTH_SHORT).show();
    }

    @Override
    public void onConfigurationChanged(Configuration newConfig) {
        super.onConfigurationChanged(newConfig);
        Toast.makeText(getApplicationContext(),"18. onConfigurationChanged()", Toast.LENGTH_SHORT).show();
    }

    @Override
    public boolean onSearchRequested() {
        super.onSearchRequested();
        Toast.makeText(getApplicationContext(),"19. onSearchRequested()", Toast.LENGTH_SHORT).show();
        return false;
    }
}

In this code, onContentChanged() is called before onCreate() method and onDetachedFromWindow() is called after onDestroy(). Why?

Answer 1

onCreate():

When an activity starts its life onCreate() is called. It is called only once in the lifecycle of an activity.

onDestroy():

onDestroy() is called when an activity finishes its life cycle. It is also called once in the lifecycle of an activity.

onContentChanged():

This hook is called whenever the content view of the screen changes (due to a call to Window.setContentView or Window.addContentView). For example you add new view to activity or want to refresh the list by calling notifyDataSetChanged().

onDetachedFromWindow():

Called when the main window associated with the activity has been detached from the window manager. For example, it is called when the current Activity goes into background or another activity came infront of current activity.