Using onSaveInstanceState with fragments in backstack?

Question

I have fragments I keep in the backstack of FragmentManager. Every fragment state is saved for orientation changes with member variables, like this for example:

@Override
public void onSaveInstanceState(Bundle outState) 
{
    super.onSaveInstanceState(outState);
    outState.putLong("userId", mUserId);
    outState.putString("username", mUsername);
}

My problem is that if there is an orientation change, since every fragment in the backstack gets called via onSaveInstanceState, I get a null pointer exception because the member variables don't exist anymore.

Any ideas on how to solve this?

Answer 1

It is possible that your member variables don't exist anymore because the FragmentManager in your Activity is dying with all of your fragments.

You need to override the method onSaveInstanceState of your Activity class as well, because you need to save the Activity state before you save the Fragments state.

As the documentation says:

There are many situations where a fragment may be mostly torn down (such as when placed on the back stack with no UI showing), but its state will not be saved until its owning activity actually needs to save its state.

UPDATE

In your Activity onSaveInstanceState and onRestoreInstanceState , try saving you Fragment references and then restore them with something like this:

public void onSaveInstanceState(Bundle outState){
    getFragmentManager().putFragment(outState, "myfragment", myfragment);
}
public void onRestoreInstanceState(Bundle inState){
    myFragment = getFragmentManager().getFragment(inState, "myfragment");
}

Tell me then if you had luck! :-)

Answer 2

Building on Jorge Gil - 'xɔɾ.xɛ xil answer Note the following:

• Don't forget call the super implementations of onSaveInstanceState() and onRestoreInstanceState().
• If you are using the support package: Please use getSupportFragmentManager() instead of getFragmentManager().
• When retrieving your original fragment you got to cast it.

Sorry for being Captain obvious!

Answer 3

Does setting the setRetainInstance on the fragment help. try out

Answer 4

I think the proper solution is to read those member variables out of savedInstanceState in onCreate which seems to be called always before onSaveInstanceState . If you process the fields in onViewCreated , they don't have the chance to get initialized before the next onSaveInstanceState (in this special case, when Fragment is in the backstack).