Develop Reference

Fragment does not call lifecycle methods

I've a fragment A. I add() it with tag like this:
fragmentTransaction.addToBackStack(special_tag);
Then I simply add() fragment B on top of fragment A. After that, I decide to remove fragment B and go back to fragment A using:
activity.fragmentManager.popBackStackImmediate(special_tag, 0)
When I reach the fragment A, it seems that fragment doesn't re-run it's lifecycle methods: onAttach(), onResume(), onCreate() ect.
Can someone explain this behavior and maybe suggest an alternative?
(I need to "refresh" the data when I come back to fragment A second time)
What is causing this result?
Is there a clean solution/work-around?
Update
Fragment B is GuidedStepFragment and does not have a .replace() function. I found that it has finishGuidedStepFragments(), but it behaves the same (it does not call fragment life cycle functions)
Situation (again):
Fragment A (Simple fragment) -> .add(Fragment B) (GuidedStepFragment) -> popBackStackImmediate() or finishGuidedStepFragments()
I add Fragment B like this:
GuidedStepFragment.add(activity.fragmentManager, fragmentB.createInstance())

Using fragmentTransaction.add(Fragment) doesn't remove Fragment A. What is actually happening is that Fragment A is still running behind Fragment B. Since Fragment A never stopped running, it's lifecycle has no need to retrigger.
Consider using fragmentTransaction.replace(Fragment) and replace the fragment in the container (fragment A) with fragment B. If you pop that transaction from the back stack, then Fragment A will reattach and follow your expected lifecycle.
Update
Since you seem to be using GuidedStepFragments from the leanback library, this is a little tricky. GuidedStepFragment actually performs replace(...) under the hood, but you're adding fragment B to a different container so the original behavior I mentioned doesn't apply.
I'm not super familiar with leanback (since it's usually only used for android tv), but I do know that you can at least do the following. If you keep track of your backstack size, when all of the GuidedStepFragments have been popped, you will have returned to your original fragment. For example, let's assume your backstack starts at zero:
activity.fragmentManager.addOnBackStackChangedListener(new FragmentManager.OnBackStackChangedListener() {
#Override
public void onBackStackChanged() {
if (activity.fragmentManager.getBackStackEntryCount() == 0){
// handle your updates
}
}
});
// the next line of code will add an entry to the backstack
GuidedStepFragment.add(activity.fragmentManager, fragmentB.createInstance());
// eventually when back is pressed and the guided fragment is removed, the backstack listener should trigger

Fragment recreation on back from another activity

I have two activities, A and B.
Activity A, has one fragment F, added dynamically via a transaction. From F, I start activity B (F.getActivity.startActivity(intent)). When I press the back button, F gets recreated. Can I avoid that?
If not, I understand I can save the fragment state, but the savedInstanceState bundle is always null. I found you must set an id in the XML, but as the fragment is dynamically created, I don't know how to set it.
Thanks.

you can manage it by adding fragment to backstack by below code
fragmentTransaction.add(R.id.containerView, fragment);
fragmentTransaction.addToBackStack("test");
and pop back the fragment state by below one
fragmentManager.popBackStack("test", FragmentManager.POP_BACK_STACK_INCLUSIVE);
hope this will be helpful.

How to restore fragment views state after returning from back stack

I have Fragment which I replace by another one. I put transaction to backstack so I can move back later. If I press back button saveInstanceState Bundle of restored Fragment is null in it's methods cause saveInstanceState method of Fragment is actually called when parent Activity instance destroyed. So how I must restore Fragment state after returning it from backstack?

This problem was mostly related to ListViews. I have found a solution in more correct managing of adapter data. I had local mAdapter variable in my Fragment which was created, populated with data and set to ListView in onResume() method of my Fragment. I have found solution in moving this code into onActivityCreated() method.

Android Fragment View State Loss When Using FragmentTransaction.replace()

I am having a pretty big issue and I am not quite understanding what is happening. I am developing an application that uses Fragments (from the support library) and am using FragmentTransaction.replace() to place new Fragments on to the back stack and replace the old one. The code looks as follows:
FragmentManager fm = getSupportFragmentManager();
FragmentTransaction ft = ft.beginTransaction();
// Animations in my res/anim folder
ft.setCustomAnimations(R.anim.slide_in_right, R.anim.slide_out_left, R.anim.slide_in_left, R.anim.slide_out_right);
ft.replace(R.id.fragment_container, newFragment, tag);
ft.addToBackStack(null);
ft.commit();
This is successful in replacing my fragment. My issue is the following. In one Fragment, I have a list of items that is built from user input. Now, when the user clicks next and then clicks the back button (to return to the list), the list is empty because the view is destroyed. Now, I have noted the following:
onSaveInstanceState is not called. I believe this is because that is only called when the parent Activity tells it to. Based on the docs: " 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.". Apparently, performing a replace on the FragmentTransaction is not one of those times. Does anyone have confirmation on this or a better explanation?
setOnRetainInstanceState(true) is not helpful in this situation. Again, I believe this has to do with info from the docs: "Control whether a fragment instance is retained across Activity re-creation (such as from a configuration change)". I am not performing any action in re-creating the activity so this is of no use.
So, I guess my main question is: is there a way to preserve the View state (simply retain the Fragment) when using replace? There is FragmentTransaction.add(), but there are a few issues with this as well. One being that the exit animation is not performed, thus the animation is not correct. Another is that the new Fragment that the old fragment (the one that is being put into a non-visible state) is still clickable. For example, if I have a ListFragment, and I place a content fragment on top of that by using add, I can still click the list items in the ListFragment.

Without being able to see the code of your fragments this is a bit of a guess, but in the past I've run into this same issue and I've found that resetting the adapter in your ListFragment in onViewStateRestored seems to do the trick.
public void onViewStateRestored (Bundle savedInstanceState)
{
super.onViewStateRestored (savedInstanceState);
setListAdapter(new ArrayAdapter(Activity, R.layout.nav_item, objects));
}
Which is weird considering the documentation states that this method is called after onActivityCreated but before onStart. But it seems that it is also called at other times because when the most recent fragment transaction is popped off the back stack this method is called before the previously replaced fragment is displayed. The activity that owns the fragments has not been paused or obscured in any way, so according to the docs onViewStateRestored should not be called since just the fragments were modified. But this seems to work anyway.

It sounds like you simply need to make sure you have properly implemented onCreateView and onDestroyView. The situation you are describing seems to indicate that when the list fragment is put on the back stack (as a result of the replace transaction) Android is calling onDestroyView to free up some resources. However, it apparently has not destroyed the list fragment because when you tap back you are getting back the same instance of the fragment.
Assuming this is all true then, when the user taps back Android will call onCreateView. Any state that you have stored in the fragment's instance variables should still be there and all you need to do is repopulate the view...perhaps set the adapter on the ListView or whatever.
Also make sure your onSaveInstanceState() callback actually does save any instance state that you need to rebuild the view. That way if the fragment actually does get completely destroyed the FragmentManager can restore the state when it needs to recrete the fragment later.

Fragment backstack bug when replacing fragments in a transaction?

Here's the scenario that causes problems:
I start an Acitivity with a ViewGroup that'll hold the presented fragments.
I load Fragment A into this ViewGroup by calling .replace() in the transaction that I save onto the backstack.
I load Fragment B into the Viewgroup, replacing Fragment A. Again, I save the transaction.
I rotate the device twice.
On the second rotation, Fragment A (which is not visible at the moment) will throw a NullPointer exception.
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?

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.