Understanding Fragment's lifeCycle methods calls during fragment transaction

Question

I created a demo to understand which all fragment lifecycle's methods are called during different cases of fragment transaction.While most of the calls are as per expectation few things I am still confused which I have written in Bold.

Suppose two fragment A and B are there and we are performing transaction between them

Case 1

When Fragment B is added to Fragment A

getActivity().getSupportFragmentManager().beginTransaction().add(R.id.container, fragementB).addToBackStack(null).commit(); 

Fragment B

onAttach

onCreate

onCreateView

onActivityCreated

onStart

onResume

No lifecycle methods of Fragment A is being called.

What i expected was?

onStop method of Fragment A is called since Fragment A is not visible

As per documentation-

Stopped- The fragment is not visible. Either the host activity has been stopped or the fragment has been removed from the activity but added to the back stack. A stopped fragment is still alive (all state and member information is retained by the system). However, it is no longer visible to the user and will be killed if the activity is killed.

Does this mean that no method of current fragment is called when new fragment is added in same activity?

Then using popBackStack() in Fragment B

Fragment B

onPause

onStop

onDestroyView

onDestroy

onDetach

No lifecycle methods of Fragment A is being called

What i expected was?

onStart method of Fragment A is called since Fragment A is visible now

Case 2

When Fragment B replaces Fragment A

getActivity().getSupportFragmentManager().beginTransaction().replace(R.id.container, fragementB).commit(); 

Fragment B

onAttach

onCreate

onCreateView

onActivityCreated

onStart

onResume

Fragment A

onPause

onStop

onDestroyView

onDestroy

onDetach

Everything was as per expectation

Case 3

When Fragment B replaces Fragment A keeping it in backstack

 getActivity().getSupportFragmentManager().beginTransaction().replace(R.id.container, fragementB).addToBackStack("tag").commit(); 

Fragment B

onAttach

onCreate

onCreateView

onActivityCreated

onStart

onResume

Fragment A

onPause

onStop

onDestroyView

onDestroy and onDetach method of Fragment A is NOT called.Why its not called?Bcoz as per documentation method replace removes any fragments that are already in the container and add your new one to the same container

Then using popBackStack() in Fragment B

Fragment A

onCreateView

onActivityCreated

onStart

onResume

Fragment B

onPause

onStop

onDestroyView

onDestroy

onDetach

Answer 1

Does this mean that no method of current fragment is called when new fragment is added in same activity?

Correct, your first fragment A will only be affected if it's removed or replaced (case 2). Simply adding another fragment will just display fragment B over fragment A and no life cycle callbacks should be called.

What i expected was?

onStart method of Fragment A is called since Fragment A is visible now

Again, since fragment B was added on top of A, fragment A is not affected by the removal of B.

onDestroy and onDetach method of Fragment A is NOT called.Why its not called?Bcoz as per documentation method replace removes any fragments that are already in the container and add your new one to the same container

Unlike a simple replace, when you add your replace transaction to the backstack you're actually keeping the first fragment attached to it's activity, only its view is destroyed.

Once you pop the backstack fragment B is removed and fragment A will just recreate its view - starting from onCreateView().