SavedInstanceState is always null even though it has an id

Question

I found many answers to this problem, but none of them seem to work. This is the code in the Activity:

@Override
public void onSaveInstanceState(Bundle savedInstanceState) {
    // Save the user's current game state
    savedInstanceState.putString(CUR_TASK, curTask);

    // Always call the superclass so it can save the view hierarchy state
    super.onSaveInstanceState(savedInstanceState);
}

as you see, super.onSaveInstanceState(savedInstanceState) is at the end, so it should work. My layout does have an id, so that should be OK too:

<android.support.v4.widget.DrawerLayout
    android:id="@+id/drawer_layout"

still, when I call startActivity to go to another Activity and return back (using the ActionBar), the savedInstanceState bundle in onCreate is null.

Answer 1

From the documentation on activity lifecycle:

Note: Because onSaveInstanceState() is not guaranteed to be called, you should use it only to record the transient state of the activity (the state of the UI)—you should never use it to store persistent data. Instead, you should use onPause() to store persistent data (such as data that should be saved to a database) when the user leaves the activity.

The method onSaveInstanceState is not used for your purpose, it's used in a case like screen rotation to save UI state. You have to switch your logic passing the values through the intent when the first Activity launches the second one and passing the values back again using onActivityResult().

In addition, I recommend you to restore your state not in onCreate() but in onRestoreInstanceState(Bundle savedInstanceState) in which you are ALWAYS sure that your savedInstanceState Bundle isn't null.