Activity Life Cycle

 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.

 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
 

Methods:-

@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();
//  super.onUserInteraction();

}
@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();
    //super.onSearchRequested()
    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();
    //super.onWindowFocusChanged(boolean bo)
    Toast.makeText(getApplic`enter code here`ationContext(),"19. onSearchRequested()", Toast.LENGTH_SHORT).show();
    return false;

}

Read More..
http://developer.android.com/reference/android/app/Activity.html#onContentChanged%28%29