There are a few scenarios in which your activity is destroyed due to normal app behavior, such as when the user presses the Back button or your activity signals its own destruction by calling . The system may also destroy your activity if it's currently stopped and hasn't been used in a long time or the system needs to free up resources and must shut down cached processes to recover memory.

When your activity is destroyed because the user presses Back or the activity finishes itself, all traces of the  instance is gone forever. However, if the system destroys the activity due to system constraints (rather than normal app behavior), then although the actual  instance is gone, the system remembers that it existed such that if the user navigates back to it, the system creates a new instance of the activity using a set of saved data that describes the state of the activity when it was destroyed.

Caution: Your activity will be destroyed and recreated each time the device configuration changes, like when the user rotates the screen.When the screen changes orientation, the system destroys and recreates the foreground activity because the screen configuration has changed and your activity might need to load alternative resources (such as the layout).

By default, the system uses the  instance state to save information about each View object in your activity layout (such as the text value entered into an  object). So, if your activity instance is destroyed and recreated, the state of the layout is restored to its previous state with no code required by you. However, your activity might have more transient state information that you'd like to restore, such as member variables that track the user's progress in the activity.

Note: In order for the Android system to restore the state of the views in your activity, each view must have a unique ID, supplied by the attribute.

解決方案1：在add Fragment時，區分一下create 狀態和recreate 狀態

public class MainActivity extends FragmentActivity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.news_articles);

        // Check that the activity is using the layout version with
        // the fragment_container FrameLayout
        if (findViewById(R.id.fragment_container) != null) {

            // However, if we're being restored from a previous state,
            // then we don't need to do anything and should return or else
            // we could end up with overlapping fragments.
            if (savedInstanceState != null) {
                return;
            }

            // Create a new Fragment to be placed in the activity layout
            HeadlinesFragment firstFragment = new HeadlinesFragment();

            // In case this activity was started with special instructions from an
            // Intent, pass the Intent's extras to the fragment as arguments
            firstFragment.setArguments(getIntent().getExtras());

            // Add the fragment to the 'fragment_container' FrameLayout
            getSupportFragmentManager().beginTransaction()
                    .add(R.id.fragment_container, firstFragment).commit();
        }
    }
}