Why Android lifecycle methods calling twice, when orentation changes from Land to Port?

Question

I know when orientation changes Android destroys and recreates current activity unless we handled Orientation changes. When orientation changes following life cycle methods get called

protected void onSaveInstanceState(Bundle outState)
protected void onStop()
protected void onDestroy()
public void onCreate(Bundle savedInstanceState)
protected void onStart()
protected void onRestoreInstanceState(Bundle savedInstanceState)
protected void onResume()

My Question is why these methods are getting called twice when I change from landscape to portrait and only once when I switch from Portrait to landscape.

Answer 1

It might be some kind of bug in emulators, It is not happening on real devices.

Answer 2

Check out Activity API - Configuration Changes, it should answer all your question.

If the configuration of the device (as defined by the Resources.Configuration class) changes, then anything displaying a user interface will need to update to match that configuration. Because Activity is the primary mechanism for interacting with the user, it includes special support for handling configuration changes.

Unless you specify otherwise, a configuration change (such as a change in screen orientation, language, input devices, etc) will cause your current activity to be destroyed, going through the normal activity lifecycle process of onPause(), onStop(), and onDestroy() as appropriate. If the activity had been in the foreground or visible to the user, once onDestroy() is called in that instance then a new instance of the activity will be created, with whatever savedInstanceState the previous instance had generated from onSaveInstanceState(Bundle).

This is done because any application resource, including layout files, can change based on any configuration value. Thus the only safe way to handle a configuration change is to re-retrieve all resources, including layouts, drawables, and strings. Because activities must already know how to save their state and re-create themselves from that state, this is a convenient way to have an activity restart itself with a new configuration.

In some special cases, you may want to bypass restarting of your activity based on one or more types of configuration changes. This is done with the android:configChanges attribute in its manifest. For any types of configuration changes you say that you handle there, you will receive a call to your current activity's onConfigurationChanged(Configuration) method instead of being restarted. If a configuration change involves any that you do not handle, however, the activity will still be restarted and onConfigurationChanged(Configuration) will not be called.