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Call a method on Popbackstack()

I replace Fragment-A with Fragment-B, and on calling popbackstack() in Fragment-B i will redirect back to Fragment-A. So I wanted to call a method that will update the list.

One more importance difference between add and replace is: replace removes the existing fragment and adds a new fragment. This means when you press back button the fragment that got replaced will be created with its onCreateView being invoked. Whereas add retains the existing fragments and adds a new fragment that means existing fragment will be active and they wont be in 'paused' state hence when a back button is pressed onCreateView is not called for the existing fragment(the fragment which was there before new fragment was added). In terms of fragment's life cycle events onPause, onResume, onCreateView and other life cycle events will be invoked in case of replace but they wont be invoked in case of add.
In Short for your use case, you need to use add and if you don't want the fragment views to overlap then you might replace the Fragment B view background color with a solid color instead of transparent.
When you add your fragment, you also have to add it to your fragment's backstack.
FragmentTransaction ft = getSupportFragmentManager.beginTransaction();
ft.replace(R.id.content, fragment, backStateName);
ft.addToBackStack(backStateName);
ft.commit();
(here R.id.content is your fragment container in your activity)
Then you have to override onBackPressed method in your activity that contains your fragments.
#Override
public void onBackPressed() {
if (getSupportFragmentManager().getBackStackEntryCount() > 1) {
getSupportFragmentManager().popBackStack();
}
}
if you want to customize your onBackPressed then you can check for your currently visible fragment in your activity and create a callback for performing action for that particular fragment. example -
#Override
public void onBackPressed() {
if (getSupportFragmentManager().getBackStackEntryCount() > 1) {
Fragment fragment = getSupportFragmentManager().findFragmentById(R.id.content);
if (fragment instanceof FragmentB) {
((FragmentB) fragment).onBackPressed();
// getSupportFragmentManager().popBackStack();
}
}
now you can add getSupportFragmentManager().popBackStack(); in your Fragment's onBackPressed() method.

Android fragment simple backstack

I have one activity containing one container that will receive 2 fragments.
Once the activity initialises i start the first fragment with:
showFragment(new FragmentA());
private void showFragment(Fragment fragment) {
getSupportFragmentManager().beginTransaction()
.replace(R.id.container, fragment, fragment.getTag())
.addToBackStack(fragment.getTag())
.commit();
}
Then when the user clicks on FragmentA, I receive this click on Activity level and I call:
showFragment(new FragmentB());
Now when I press back button it returns to fragment A (thats correct) and when i press again back button it show empty screen (but stays in the same activity). I would like it to just close the app (since the activity has no parent).
There are a lot of posts related with Fragments and backstack, but i can't find a simple solution for this. I would like to avoid the case where I have to check if im doing back press on Fragment A or Fragment B, since i might extend the number of Fragments and I will need to maintain that method.

You are getting blank screen because when you add first fragment you are calling addToBackStack() due to which you are adding a blank screen unknowingly!
now what you can do is call the following method in onBackPressed() and your problem will be solved
public void moveBack()
{
//FM=fragment manager
if (FM != null && FM.getBackStackEntryCount() > 1)
{
FM.popBackStack();
}else {
finish();
}
}
DO NOT CALL SUPER IN ONBACKPRESSED();
just call the above method!

addToBackStack(fragment.getTag())
use it for fragment B only, not for fragment A

I think your fragment A is not popped out correctly, try to use add fragment rather replace to have proper back navigation, however You can check count of back stack using:
FragmentManager fragmentManager = getSupportFragmentManager();
int count = fragmentManager.getBackStackEntryCount();
and you can also directly call finish() in activity onBackPressed() when you want your activity to close on certain fragment count.

Prevent reverting a fragment transaction

I have added a fragment transaction to the back stack with addToBackStack(). Is it possible to forbid reverting the fragment transaction when the user presses the back button? I do not want popBackStack() because this actually reverts the transaction.

Override the onBackPressed() method where you are pressing back button and remove super.onBackPressed();
#Override
public void onBackPressed() {
//remove super.onBackPressed(); from here
//And provide your functionality
}

Which callback method called when coming back to a fragment from another added fragment?

I have a fragment [A], and I add a new fragment [B] through this code:
FragmentTransaction ft = getSupportFragmentManager().beginTransaction()
.addToBackStack(null).**add**(R.id.activity_content, fragment).commit();
I want to run some code when I come back to [A] from [B] using a back button. However, When clicking back button on fragment [B], none of the callback methods on [A] are called.
Given that I am adding a fragment through "add" and not "replace," are there any callback methods I can override in [A]?

For this case you should probably add an OnBackstackChangedListener:
// Add this after the transaction...
getSupportFragmentManager().addOnBackStackChangedListener(new OnBackStackChangedListener() {
#Override
public void onBackStackChanged() {
// Do your logic here. Probably want to remove the
// listener at this point too.
}
});

Query with Fragment backstack

Say I have 2 fragments: A and B
Fragment A is on top. Now, I add fragment B keeping A in backstack.
Now when back button is pressed, B is removed and A comes on top.
Is there any callback method in A which gets called at this point?
Note: onResume is closely bound with activity, thus it is not called. Fragment's onResume() is called only when activity's onResume() is called.

Sorry but there is no call back, as popToBackStack results to recreate fragments only in case of replace transaction and not in add.

You may want to add OnBackStackChangedListener to your fragment manager and monitor BackStackEntryCount
getSupportFragmentManager().addOnBackStackChangedListener(new OnBackStackChangedListener() {
public void onBackStackChanged() {
Log.i(TAG, "back stack changed ");
int backCount = getSupportFragmentManager().getBackStackEntryCount();
}
}
});
Once you get this trigger, you can pass a message from activity to fragment A as described in this article Deliver a Message to a Fragment or probably have an Observer in your Fragment observe an Observable in your main Activity

onViewStateRestored() is called when fragment is shown again.