What is the difference between enter/exit and popEnter/popExit animations?

In setCustomAnimations() it takes four resource id for the animation. Not really understand them. If someone having clearer picture of it it would be appreciated if you could explain.

Let's say having fragment A add in the place holder and backstack.

FragmentTransaction ft = fm.beginTransaction();
        ft.replace(R.id.holder, fragA, FragmentA.FRAGMENT_NAME);
        ft.addToBackStack(FragmentA.FRAGMENT_NAME);
        ft.setCustomAnimations(R.anim.slide_in_from_bottom, R.anim.slide_in_from_top, R.anim.slide_in_from_left, R.anim.slide_in_from_right);
        ft.show(frag);
        ft.commit();

And the replace with fragment B:

FragmentTransaction ft = fm.beginTransaction();
        ft.replace(R.id.holder, fragB, FragmentB.FRAGMENT_NAME);
        ft.addToBackStack(FragmentB.FRAGMENT_NAME);
        ft.setCustomAnimations(R.anim.slide_in_from_bottom, R.anim.slide_in_from_top, R.anim.slide_in_from_left, R.anim.slide_in_from_right);
        ft.show(frag);
        ft.commit();

next time if do a popstack()

fm.popBackStackImmediate(FragmentB.FRAGMENT_NAME,
                                FragmentManager.POP_BACK_STACK_INCLUSIVE);

Which transaction's animation it will be running from?

/**
 * Set specific animation resources to run for the fragments that are
 * entering and exiting in this transaction. The <code>popEnter</code>
 * and <code>popExit</code> animations will be played for enter/exit
 * operations specifically when popping the back stack.
 */
public abstract FragmentTransaction setCustomAnimations(@AnimRes int enter,
        @AnimRes int exit, @AnimRes int popEnter, @AnimRes int popExit);

Let's start simple case:

Replace Fragment A with Fragment B (your second code snippet)

• Fragment B runs enter animation
• Fragment A runs exit animation

Press back button and undo the replace operation

• Fragment B runs popExit animation
• Fragment A runs popEnter animation

Now to answer your question.

You don't say if the container already has a fragment or not. Let's consider both cases:

1. Container already had a fragment (let's call it Fragment 0) when the first operation to replace with Fragment A was called. When popping the entire stack:

   • Fragment B runs popExit animation (set in second snippet)
   • Fragment 0 runs popEnter animation (set in first snippet)

2. Container was empty so replacing with Fragment A was essentially an add operation. When popping entire stack:

   • Fragment B runs popExit animation (set in second snippet)
   • No popEnter animation runs since container is now empty