How to determine fragment restored from backstack

Question

Been searching for this issue for a while to no avail now:

How to determine fragment is being restored from backstack? I'm using the compatibility library and a ListFragment inside a FragmentActivity. When an item inside ListFragment is selected, a new Fragment is started to replace the ListFragment.

I noticed that when the FragmentActivity gets paused, the Fragment's onSaveInstanceState is called. But when the Fragment is put into the back stack via FragmentTransaction, onSaveInstanceState doesn't get called, then the lifecycle methods onCreateView and onActivityCreated gets called with null savedInstanceState Bundle.

I'm asking this because I want to load some data when the Fragment is created or restored, but not so when user comes back via. backstack.

I've looked at How to check if Fragment was restored from a backstack? but want to add more details in hopes this would incite an answer.

Edit: just noticed http://developer.android.com/reference/android/app/Fragment.html#onSaveInstanceState(android.os.Bundle) says

Note however: this method may be called at any time before onDestroy(). 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.

So onSaveInstanceState is definitely out of the question...

Answer 1

I think that most simple way is do this for example in onViewCreated() method:

if (savedInstanceState == null && !mAlreadyLoaded) {     mAlreadyLoaded = true;      // Do this code only first time, not after rotation or reuse fragment from backstack } 

Because when android put fragment on backstack, it only destroy its view, but don't kill instance itself, so mAlreadyLoaded will be still true when fragment will be restored from backstack.

Answer 2

getSupportFragmentManager().addOnBackStackChangedListener(new OnBackStackChangedListener() {                 public void onBackStackChanged() {                 Log.i(TAG, "back stack changed ");                 int backCount = getSupportFragmentManager().getBackStackEntryCount();                 if (backCount == 0){                                    // block where back has been pressed. since backstack is zero.                 }             }         }); 

use this addOnBackStackChangedListener.