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Here's the scenario that causes problems:
This exception is thrown by Fragment A, because I'm saving some values of Views (EditTexts e.g.) in its onSaveInstanceState() method. It seems, that on the second rotation, the system doesn't instantiate these Views, so when I'm asking their values, I get a NullPointer exception. Can this be avoided somehow? Or is using .replace operations in a fragment transcation saved onto the backstack unadvised?
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For more information on navigating with animations and transitions, see Fragment transactions and Navigate between fragments using animations. Calling addToBackStack() commits the transaction to the back stack. The user can later reverse the transaction and bring back the previous fragment by pressing the Back button.
How do you delete Backstacks on Android? Use finishAffinity() to clear all backstack with existing one. Suppose, Activities A, B and C are in stack, and finishAffinity(); is called in Activity C, – Activity B will be finished / removing from stack. – Activity A will be finished / removing from stack.
Since you want only one back stack entry per Fragment , make the back state name the Fragment's class name (via getClass(). getName() ). Then when replacing a Fragment , use the popBackStackImmediate() method. If it returns true, it means there is an instance of the Fragment in the back stack.
Use replace() to replace an existing fragment in a container with an instance of a new fragment class that you provide. Calling replace() is equivalent to calling remove() with a fragment in a container and adding a new fragment to that same container. transaction. commit();
I've had this but can't quite recollect the specifics of what I did to fix but generally speaking (and apologies for the brain dump) I do the following:
Call setRetainInstance(true) in onCreate to avoid fragment recreation
Save the state of edit controls etc. in onSaveInstanceState to be used if activity is killed and you get restored with a non-null bundle (you shouldn't get a non-null bundle on an orientation change with 1.)
Maintain edit control values in member variables (as the fragment is not going to be recreated) ensuring they get updated in an onDestroyView from the edit controls and then use them to restore the edit control values in onCreateView
Have a flag which I set to true in onCreateView and false in onDestroyView and ensure I don't touch UI controls when the view is not around.
BTW Using replace while adding the transaction to the back stack is perfectly OK.
Hope there's something in there that helps. Peter.
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