恢复w / o savedInstanceState后如何恢复片段状态？

Question

in my app an FragmentActivity contains a simple ListFragment and I want to preserve the position to which the user has scrolled to. I did the following:

private int initialScrollPosition = 0;
private int initialScrollYOffset = 0;

@Override
public void onSaveInstanceState (Bundle outState) {
    outState.putInt(SCROLL_POSITION, this.getListView().getFirstVisiblePosition());
    View firstVisibleItemView = this.getListView().getChildAt(0);
    outState.putInt(SCROLL_Y_OFFSET, (firstVisibleItemView == null) ? 0 : firstVisibleItemView.getTop());
}

@Override
public void onActivityCreated (Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);
    this.restoreState(savedInstanceState);
}

private void restoreState(Bundle savedInstanceState) {
    if(savedInstanceState != null
            && savedInstanceState.containsKey(SCROLL_POSITION)) {
        this.initialScrollPosition = savedInstanceState.getInt(SCROLL_POSITION);
    }
    if(savedInstanceState != null
            && savedInstanceState.containsKey(SCROLL_Y_OFFSET)) {
        this.initialScrollYOffset = savedInstanceState.getInt(SCROLL_Y_OFFSET);
    }
}

@Override
public void onStart () {
    super.onStart();
    // some other GUI stuff
    this.getListView().setSelectionFromTop(this.initialScrollPosition, this.initialScrollYOffset);
}

This solution works fine for things like display orientation changes or moving from one Activity of my app to the next.

But if I fire up the app, scroll a bit, go back to home, and restore the App from Recents, onActivityCreated (or any other callbacks with the savedInstanceState Bundle ) is not called and therefore the state cannot be restored.

Therefore I have two questions:

1. What can I do to get the savedInstanceState after resuming without the onXXXCreated callbacks?
2. What exactly is the lifecycle doing there. I'd like to understand, why my approach fails.

Thank you very much for any insight!

Solution:

Thx to André! I changed my onSaveInstanceState to this:

@Override
public void onSaveInstanceState (Bundle outState) {
    this.initialScrollPosition = this.getListView().getFirstVisiblePosition();
    View firstVisibleItemView = this.getListView().getChildAt(0);
    this.initialScrollYOffset = (firstVisibleItemView == null) ? 0 : firstVisibleItemView.getTop();
    outState.putInt(SCROLL_POSITION, this.initialScrollPosition);
    outState.putInt(SCROLL_Y_OFFSET, this.initialScrollYOffset);
}

Answer 1

If your app is brought to front using the recent apps button, it might be that it isn't recreated, because the system didn't finish it yet. In that case only onResume() and following callbacks are invoked.

Conclusion: try to restore your position in onResume() , store the positions in onPause() (for recent app switches where the activity isn't recreated), extract the positions from savedInstanceState bundle (for orientation change where the activity is recreated).