Is this the right way to clean-up Fragment back stack when leaving a deeply nested stack

Question

I m using the Android Compatibility library to implement fragments and have extended the layout sample so that a fragment contains a button which fires off another fragment   In the selection pane on the left I have 5 selectable items - A B C D E   Each loads up a fragment  via FragmentTransaction replace  in the details pane - a b c d e  Now I ve extended fragment e to contain a button which loads up another fragment e1 also in the details pane  I ve done this on fragment e s onClick method as follows   FragmentTransaction ft   getActivity   getSupportFragmentManager   beginTransaction    ft replace R id details frag  newFrag   ft setTransition FragmentTransaction TRANSIT FRAGMENT OPEN   ft addToBackStack null   ft commit      If I make the following selections   E - e - e1 - D - E   Then fragment e is in the details pane  This is fine and what I want  However  if I hit the back button at this point it does nothing  I have to click it twice because e1 is still on the stack  Furthermore after clicking around I got a null pointer exception in onCreateView   To  solve  this problem I added the following whenever A B C D E is selected   FragmentManager fm   getActivity   getSupportFragmentManager    for int i   0  i  lt  fm getBackStackEntryCount      i        fm popBackStack        Just wondering whether this is the correct solution or whether I should be doing something different

User · Answer

pop back stack all the way     final FragmentManager fm   getSherlockActivity   getSupportFragmentManager        int entryCount   fm getBackStackEntryCount         while  entryCount--  gt  0            fm popBackStack

User · Answer

Well there are a few ways to go about this depending on the intended behavior  but this link should give you all the best solutions and not surprisingly is from Dianne Hackborn  http   groups google com group android-developers browse thread thread d2a5c203dad6ec42  Essentially you have the following options   Use a name for your initial back stack state and use FragmentManager popBackStack String name  FragmentManager POP BACK STACK INCLUSIVE   Use FragmentManager getBackStackEntryCount   getBackStackEntryAt   getId   to retrieve the ID of the first entry on the back stack  and FragmentManager popBackStack int id  FragmentManager POP BACK STACK INCLUSIVE   FragmentManager popBackStack null  FragmentManager POP BACK STACK INCLUSIVE  is supposed to pop the entire back stack     I think the documentation for that is just wrong    Actually I guess it just doesn t cover the case where you pass in POP BACK STACK INCLUSIVE

User · Answer

As written in How to pop fragment off backstack and by LarsH here  we can pop several fragments from top down to specifical tag  together with the tagged fragment  using this method   fragmentManager  popBackStack   frag   FragmentManager POP BACK STACK INCLUSIVE     Substitute  frag  with your fragment s tag  Remember that first we should add the fragment to backstack with   fragmentTransaction addToBackStack  frag     If we add fragments with addToBackStack null   we won t pop fragments that way

User · Answer

Thanks to Joachim answer  I use the code to clear all back stack entry finally      In your FragmentActivity use getSupprotFragmentManager   to get the FragmentManager      Clear all back stack  int backStackCount   getSupportFragmentManager   getBackStackEntryCount    for  int i   0  i  lt  backStackCount  i              Get the back stack fragment id      int backStackId   getSupportFragmentManager   getBackStackEntryAt i  getId         getSupportFragmentManager   popBackStack backStackId           FragmentManager POP BACK STACK INCLUSIVE         end of for

User · Answer

The other clean solution if you don t want to pop all stack entries     getSupportFragmentManager   popBackStack null  FragmentManager POP BACK STACK INCLUSIVE   getSupportFragmentManager   beginTransaction   replace R id home activity container  fragmentInstance  addToBackStack null  commit      This will clean the stack first and then load a new fragment  so at any given point you ll have only single fragment in stack

User · Answer

I m using a similar code as those that use the while loop but I call the entry count in every loop    so I suppose it s somewhat slower  FragmentManager manager   getFragmentManager    while  manager getBackStackEntryCount    gt  0           manager popBackStackImmediate

User · Answer

I have researched a lot for cleaning Backstack  and finally see Transaction BackStack and its management  Here is the solution that worked best for me       CLEAR BACK STACK      private void clearBackStack             final FragmentManager fragmentManager   getSupportFragmentManager            while  fragmentManager getBackStackEntryCount      0                fragmentManager popBackStackImmediate                      The above method loops over all the transactions in the backstack and removes them immediately one at a time   Note  above code sometime not work and i face ANR because of this code so please do not try this    Update below method remove all fregment of that  name  from backstack     FragmentManager fragmentManager   getSupportFragmentManager    fragmentManager popBackStack  name  FragmentManager POP BACK STACK INCLUSIVE      name If non-null  this is the name of a previous back state to look for  if found  all states up to that state will be popped   The POP BACK STACK INCLUSIVE flag can be used to control whether the named state itself is popped  If null  only the top state is popped

[android] Is this the right way to clean-up Fragment back stack when leaving a deeply nested stack?

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