Problems with Android Fragment back stack

Question

I ve got a massive problem with the way the android fragment backstack seems to work and would be most grateful for any help that is offered   Imagine you have 3 Fragments   1   2   3   I want the user to be able to navigate  1   gt   2   gt   3  but on the way back  pressing back button   3   gt   1    As I would have imagined this would be accomplished by not calling addToBackStack     when creating the transaction that brings fragment  2  into the fragment holder defined in XML   The reality of this seems as though that if I dont want  2  to appear again when user presses back button on  3   I must not call addToBackStack in the transaction that shows fragment  3   This seems completely counter-intuitive  perhaps coming from the iOS world    Anyway if i do it this way  when I go from  1   gt   2  and press back I arrive back at  1  as expected   If I go  1   gt   2   gt   3  and then press back I jump back to  1   as expected   Now the strange behavior happens when I try and jump to  2  again from  1   First of all  3  is briefly displayed before  2  comes into view  If I press back at this point  3  is displayed  and if I press back once again the app exits   Can anyone help me to understand whats going on here     And here is the layout xml file for my main activity     lt  xml version  1 0  encoding  utf-8   gt   lt LinearLayout xmlns android  http   schemas android com apk res android            android layout width  fill parent            android layout height  fill parent            android orientation  vertical   gt    lt fragment         android id    id headerFragment          android layout width  match parent          android layout height  wrap content          class  com fragment test FragmentControls   gt       lt  -- Preview  layout  layout details -- gt   lt  fragment gt   lt FrameLayout         android id    id detailFragment          android layout width  match parent          android layout height  fill parent             gt         Update This is the code I m using to build by nav heirarchy      Fragment frag      FragmentTransaction transaction          Create The first fragment  1   add it to the view  BUT Dont add the transaction to the backstack     frag   new Fragment1         transaction   getSupportFragmentManager   beginTransaction        transaction replace R id detailFragment  frag       transaction commit           Create the second  2  fragment  add it to the view and add the transaction that replaces the first fragment to the backstack     frag   new Fragment2         transaction   getSupportFragmentManager   beginTransaction        transaction replace R id detailFragment  frag       transaction addToBackStack null       transaction commit            Create third fragment  Dont add this transaction to the backstack  because we dont want to go back to  2       frag   new Fragment3        transaction   getSupportFragmentManager   beginTransaction        transaction replace R id detailFragment  frag       transaction commit             END OF SETUP CODE-------------------------       NOW        Press back once and then issue the following code      frag   new Fragment2        transaction   getSupportFragmentManager   beginTransaction        transaction replace R id detailFragment  frag       transaction addToBackStack null       transaction commit           Now press back again and you end up at fragment  3  not  1    Many thanks

User · Answer

First of all thanks  Arvis for an eye opening explanation   I prefer different solution to the accepted answer here for this problem  I don t like messing with overriding back behavior any more than absolutely necessary and when I ve tried adding and removing fragments on my own without default back stack poping when back button is pressed I found my self in fragment hell    If you  add f2 over f1 when you remove it f1 won t call any of callback methods like onResume  onStart etc  and that can be very unfortunate   Anyhow this is how I do it   Currently on display is only fragment f1   f1 -  f2  Fragment2 f2   new Fragment2    this getActivity   getSupportFragmentManager   beginTransaction   replace R id main content f2  addToBackStack null  commit      nothing out of the ordinary here  Than in fragment f2 this code takes you to fragment f3   f2 -  f3  Fragment3 f3   new Fragment3    getActivity   getSupportFragmentManager   popBackStack    getActivity   getSupportFragmentManager   beginTransaction   replace R id main content  f3  addToBackStack null  commit      I m not sure by reading docs if this should work  this poping transaction method is said to be asynchronous  and maybe a better way would be to call popBackStackImmediate    But as far I can tell on my devices it s working flawlessly   The said alternative would be   final FragmentActivity activity   getActivity    activity getSupportFragmentManager   popBackStackImmediate    activity getSupportFragmentManager   beginTransaction   replace R id main content  f3  addToBackStack null  commit      Here there will actually be brief going back to f1 beofre moving on to f3  so a slight glitch there   This is actually all you have to do  no need to override back stack behavior

User · Answer

I had a similar issue where I had 3 consecutive fragments in the same Activity  M1 F0 -  M1 F1 -  M1 F2  followed by a call to a new Activity M2   If the user pressed a button in  M2  I wanted to return to  M1 F1  instead of  M1 F2  which is what back press behavior already did   In order to accomplish this I remove  M1 F2   call show on  M1 F1   commit the transaction  and then add  M1 F2  back by calling it with hide  This removed the extra back press that would have otherwise been left behind      Remove  M1 F2  to avoid having an extra entry on back press when returning from M2 final FragmentTransaction ftA   fm beginTransaction    ftA remove M1F2Fragment   ftA show M1F1Fragment   ftA commit    final FragmentTransaction ftB   fm beginTransaction    ftB hide M1F2Fragment   ftB commit        Hi     After doing this code  I m not able to see value of Fragment2 on pressing Back Key      My Code   FragmentTransaction ft   fm beginTransaction    ft add R id frame  f1   ft remove f1    ft add R id frame  f2   ft addToBackStack null    ft remove f2   ft add R id frame  f3    ft commit      Override     public boolean onKeyDown int keyCode  KeyEvent event            if keyCode    KeyEvent KEYCODE BACK               Fragment currentFrag    getFragmentManager   findFragmentById R id frame               FragmentTransaction transaction   getFragmentManager   beginTransaction                 if currentFrag    null                   String name   currentFrag getClass   getName                              if getFragmentManager   getBackStackEntryCount      0                             else                  getFragmentManager   popBackStack                    removeCurrentFragment                               return super onKeyDown keyCode  event         public void removeCurrentFragment                 FragmentTransaction transaction   getFragmentManager   beginTransaction            Fragment currentFrag    getFragmentManager   findFragmentById R id frame            if currentFrag    null               transaction remove currentFrag                     transaction commit

User · Answer

Right    after much hair pulling I ve finally worked out how to make this work properly   It seems as though fragment  3  is not removed from the view when back is pressed so you have to do it manually   First of all  dont use replace   but instead use remove and add separately  It seems as though replace   doesnt work properly   The next part to this is overriding the onKeyDown method and remove the current fragment every time the back button is pressed    Override public boolean onKeyDown int keyCode  KeyEvent event        if  keyCode    KeyEvent KEYCODE BACK                if  getSupportFragmentManager   getBackStackEntryCount      0                        this finish                return false                    else                       getSupportFragmentManager   popBackStack                removeCurrentFragment                 return false                          return super onKeyDown keyCode  event       public void removeCurrentFragment         FragmentTransaction transaction   getSupportFragmentManager   beginTransaction         Fragment currentFrag    getSupportFragmentManager   findFragmentById R id detailFragment         String fragName    NONE        if  currentFrag  null          fragName   currentFrag getClass   getSimpleName          if  currentFrag    null          transaction remove currentFrag        transaction commit         Hope this helps

User · Answer

After  Arvis reply i decided to dig even deeper and I ve written a tech article about this here  http   www andreabaccega com blog 2015 08 16 how-to-avoid-fragments-overlapping-due-to-backstack-nightmare-in-android   For the lazy developers around  My solution consists in always adding the transactions to the backstack and perform an extra FragmentManager popBackStackImmediate   when needed  automatically    The code is very few lines of code and  in my example  I wanted to skip from C to A without jumping back to  B  if the user didn t went deeper in the backstack  ex from C navigates to D    Hence the code attached would work as follow A -  B -  C  back  -  A  amp  A -  B -  C -  D  back  -  C  back  -  B  back  -  A  where   fm beginTransaction   replace R id content  new CFragment    commit     were issued from  B  to  C  as in the question   Ok Ok here is the code     public static void performNoBackStackTransaction FragmentManager fragmentManager  String tag  Fragment fragment      final int newBackStackLength   fragmentManager getBackStackEntryCount    1     fragmentManager beginTransaction          replace R id content  fragment  tag         addToBackStack tag         commit       fragmentManager addOnBackStackChangedListener new FragmentManager OnBackStackChangedListener          Override     public void onBackStackChanged           int nowCount   fragmentManager getBackStackEntryCount          if  newBackStackLength    nowCount               we don t really care if going back or forward  we already performed the logic here          fragmentManager removeOnBackStackChangedListener this            if   newBackStackLength  gt  nowCount        user pressed back           fragmentManager popBackStackImmediate

User · Answer

If you are Struggling with addToBackStack    amp  popBackStack   then simply use  FragmentTransaction ft  getSupportFragmentManager   beginTransaction    ft replace R id content frame  new HomeFragment     Home    ft commit       In your Activity In OnBackPressed   find out fargment by tag and then do your stuff  Fragment home   getSupportFragmentManager   findFragmentByTag  Home     if  home instanceof HomeFragment  amp  amp  home isVisible             do you stuff     For more Information https   github com DattaHujare NavigationDrawer   I never use addToBackStack   for handling fragment

User · Answer

I think  when I read your story that  3  is also on the backstack  This explains why you see it flashing up   Solution would be to never set  3  on the stack

User · Answer

executePendingTransactions     commitNow   not worked    Worked in androidx  jetpack    private final FragmentManager fragmentManager   getSupportFragmentManager     public void removeFragment FragmentTag tag        Fragment fragmentRemove   fragmentManager findFragmentByTag tag toString         if  fragmentRemove    null            fragmentManager beginTransaction                    remove fragmentRemove                   commit                fix by  Ogbe         fragmentManager popBackStackImmediate tag toString                 FragmentManager POP BACK STACK INCLUSIVE

User · Answer

I know it s a old quetion but i got the same problem and fix it like this   First  Add Fragment1 to BackStack with a name  e g  Frag1     frag   new Fragment1     transaction   getSupportFragmentManager   beginTransaction    transaction replace R id detailFragment  frag   transaction addToBackStack  Frag1    transaction commit      And then  Whenever you want to go back to Fragment1  even after adding 10 fragments above it   just call popBackStackImmediate with the name   getSupportFragmentManager   popBackStackImmediate  Frag1   0     Hope it will help someone

User · Answer

Explanation  on what s going on here   If we keep in mind that  replace   is equal with  remove   add   that we know by the documentation      Replace an existing fragment that was added to a container  This is essentially the same as calling remove Fragment  for all currently added fragments that were added with the same containerViewId and then add int  Fragment  String  with the same arguments given here    then what s happening is like this  I m adding numbers to the frag to make it more clear       transaction replace R id detailFragment  frag1   Transaction remove null  add frag1      frag1 on view     transaction replace R id detailFragment  frag2  addToBackStack null   Transaction remove frag1  add frag2  addToBackStack null      frag2 on view     transaction replace R id detailFragment  frag3   Transaction remove frag2  add frag3      frag3 on view    here all misleading stuff starts to happen   Remember that  addToBackStack   is saving only transaction not the fragment as itself  So now we have frag3 on the layout    lt  press back button  gt     System pops the back stack and find the following saved back entry to be reversed      Transaction remove frag1  add frag2      so the system makes that transaction backward       tries to remove frag2  is not there  so it ignores  and re-add frag1     make notice that system doesn t realise that there s a frag3 and does nothing with it    so it still there attached to view Transaction remove null  add frag1    frag1  frag3 on view  OVERLAPPING      transaction replace R id detailFragment  frag2  addToBackStack null   Transaction remove frag3  add frag2  addToBackStack null     frag2 on view   lt  press back button  gt     system makes saved transaction backward Transaction remove frag2  add frag3    frag3 on view   lt  press back button  gt     no more entries in BackStack  lt  app exits  gt    Possible solution  Consider implementing FragmentManager BackStackChangedListener to watch for changes in the back stack and apply your logic in onBackStackChanged   methode    Trace a count of transaction  Check particular transaction by name FragmentTransaction addToBackStack String name   Etc

[android] Problems with Android Fragment back stack

Examples related to android

Examples related to android-fragments

Examples related to back-stack