How to resume Fragment from BackStack if exists

Question

I am learning how to use fragments  I have three instances of Fragment that are initialized at the top of the class  I am adding the fragment to an activity like this   Declaring and initializing   Fragment A   new AFragment    Fragment B   new BFragment    Fragment C   new CFragment      Replacing Adding   FragmentTransaction ft   getSupportFragmentManager   beginTransaction    ft replace R id content frame  A   ft addToBackStack null   ft commit      These snippets are working properly  Every fragment is attached to the activity  and is saved to the back stack without any problem   So when I launch A  C  and then B  the stack looks like this        B   C   A        And when I press the  back  button  B is destroyed and C is resumed   But  when I launch fragment A a second time  instead of resuming from back stack  it is added at the top of the back stack       A   C   A        But I want to resume A and destroy all fragments on top of it  if any   Actually  I just like the default back stack behavior    How do I accomplish this   Expected   A should be resumed and top fragments should be destroyed                A        Edit   suggested by A--C   This is my trying code   private void selectItem int position            Fragment problemSearch   null  problemStatistics   null          FragmentManager manager   getSupportFragmentManager            FragmentTransaction ft   manager beginTransaction            String backStateName   null          Fragment fragmentName   null          boolean fragmentPopped   false          switch  position            case 0              fragmentName   profile              break          case 1              fragmentName   submissionStatistics              break          case 2              fragmentName   solvedProblemLevel              break          case 3              fragmentName   latestSubmissions              break          case 4              fragmentName   CPExercise              break          case 5              Bundle bundle   new Bundle                bundle putInt  problem no   problemNo               problemSearch   new ProblemWebView                problemSearch setArguments bundle               fragmentName   problemSearch              break          case 6              fragmentName   rankList              break          case 7              fragmentName   liveSubmissions              break          case 8              Bundle bundles   new Bundle                bundles putInt  problem no   problemNo               problemStatistics   new ProblemStatistics                problemStatistics setArguments bundles               fragmentName   problemStatistics          default              break                    backStateName   fragmentName getClass   getName            fragmentPopped   manager popBackStackImmediate backStateName  0           if   fragmentPopped                ft replace R id content frame  fragmentName                     ft setTransition FragmentTransaction TRANSIT FRAGMENT FADE           ft addToBackStack backStateName           ft commit                I am using drawer layout         mDrawerList setItemChecked position  true           setTitle title position            mDrawerLayout closeDrawer mDrawerList           The problem is  when I launch A and then B  then press  back   B is removed and A is resumed  and pressing  back  a second time should exit the app  But it is showing a blank window and I have to press back a third time to close it   Also  when I launch A  then B  then C  then B again     Expected            B   A        Actual        B   B   A        Should I override onBackPressed   with any customization or am I missing something

User · Answer

I know this is quite late to answer this question but I resolved this problem by myself and thought worth sharing it with everyone.`

public void replaceFragment(BaseFragment fragment) {
    FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
    final FragmentManager fManager = getSupportFragmentManager();
    BaseFragment fragm = (BaseFragment) fManager.findFragmentByTag(fragment.getFragmentTag());
    transaction.setCustomAnimations(R.anim.enter_from_right, R.anim.exit_to_left, R.anim.enter_from_left, R.anim.exit_to_right);

    if (fragm == null) {  //here fragment is not available in the stack
        transaction.replace(R.id.container, fragment, fragment.getFragmentTag());
        transaction.addToBackStack(fragment.getFragmentTag());
    } else { 
        //fragment was found in the stack , now we can reuse the fragment
        // please do not add in back stack else it will add transaction in back stack
        transaction.replace(R.id.container, fragm, fragm.getFragmentTag()); 
    }
    transaction.commit();
}

And in the onBackPressed()

 @Override
public void onBackPressed() {
    if(getSupportFragmentManager().getBackStackEntryCount()>1){
        super.onBackPressed();
    }else{
        finish();
    }
}

User · Answer

Step 1  Implement an interface with your activity class  public class AuthenticatedMainActivity extends Activity implements FragmentManager OnBackStackChangedListener        Override     protected void onCreate Bundle savedInstanceState                                  FragmentManager fragmentManager   getFragmentManager                       fragmentManager beginTransaction   add R id frame container fragment   First   addToBackStack null  commit               private void switchFragment Fragment fragment                     FragmentManager fragmentManager   getFragmentManager          fragmentManager beginTransaction            replace R id frame container  fragment  addToBackStack  Tag   commit                Override     public void onBackStackChanged         FragmentManager fragmentManager   getFragmentManager         System out println   Class  SummaryUser   onBackStackChanged                  fragmentManager getBackStackEntryCount          int count   fragmentManager getBackStackEntryCount            when a fragment come from another the status will be zero     if count    0            System out println  again loading user data                reload the page if user saved the profile data          if  objPublicDelegate checkNetworkStatus                  objPublicDelegate showAlertDialog  Warning                         Please check your internet connection              else                objLoadingDialog show  Refreshing data                     mNetworkMaster runUserSummaryAsync                          IMPORTANT  remove the current fragment from stack to avoid new instance         fragmentManager removeOnBackStackChangedListener this            end if                 Step 2  When you call the another fragment add this method   String backStateName   this getClass   getName     FragmentManager fragmentManager   getFragmentManager    fragmentManager addOnBackStackChangedListener this     Fragment fragmentGraph   new GraphFragment    Bundle bundle   new Bundle    bundle putString  graphTag    view getTag   toString     fragmentGraph setArguments bundle    fragmentManager beginTransaction    replace R id content frame  fragmentGraph   addToBackStack backStateName   commit

User · Answer

I think  this method my solve your problem    public static void attachFragment   int fragmentHolderLayoutId  Fragment fragment  Context context  String tag           FragmentManager manager      AppCompatActivity  context   getSupportFragmentManager         FragmentTransaction ft   manager beginTransaction          if  manager findFragmentByTag   tag      null       No fragment in backStack with same tag           ft add   fragmentHolderLayoutId  fragment  tag            ft addToBackStack   tag            ft commit               else           ft show   manager findFragmentByTag   tag     commit               which was originally posted in  This Question

User · Answer

getFragmentManager   addOnBackStackChangedListener new FragmentManager OnBackStackChangedListener           Override     public void onBackStackChanged              if getFragmentManager   getBackStackEntryCount    0                onResume

User · Answer

Easier solution will be changing this line  ft replace R id content frame  A   to ft add R id content frame  A    And inside your XML layout please use     android background   color white    android clickable  true    android focusable  true    Clickable means that it can be clicked by a pointer device or be tapped by a touch device   Focusable means that it can gain the focus from an input device like a keyboard  Input devices like keyboards cannot decide which view to send its input events to based on the inputs itself  so they send them to the view that has focus

User · Answer

Reading the documentation  there is a way to pop the back stack based on either the transaction name or the id provided by commit  Using the name may be easier since it shouldn t require keeping track of a number that may change and reinforces the  unique back stack entry  logic   Since you want only one back stack entry per Fragment  make the back state name the Fragment s class name  via getClass   getName     Then when replacing a Fragment  use the popBackStackImmediate   method  If it returns true  it means there is an instance of the Fragment in the back stack  If not  actually execute the Fragment replacement logic   private void replaceFragment  Fragment fragment     String backStateName   fragment getClass   getName       FragmentManager manager   getSupportFragmentManager      boolean fragmentPopped   manager popBackStackImmediate  backStateName  0      if   fragmentPopped     fragment not in back stack  create it      FragmentTransaction ft   manager beginTransaction        ft replace R id content frame  fragment       ft addToBackStack backStateName       ft commit              EDIT     The problem is - when i launch A and then B  then press back button  B   is removed and A is resumed  and pressing again back button should   exit the app  But it is showing a blank window and need another press   to close it    This is because the FragmentTransaction is being added to the back stack to ensure that we can pop the fragments on top later  A quick fix for this is overriding onBackPressed   and finishing the Activity if the back stack contains only 1 Fragment    Override public void onBackPressed      if  getSupportFragmentManager   getBackStackEntryCount      1       finish          else       super onBackPressed            Regarding the duplicate back stack entries  your conditional statement that replaces the fragment if it hasn t been popped is clearly different than what my original code snippet s  What you are doing is adding to the back stack regardless of whether or not the back stack was popped   Something like this should be closer to what you want   private void replaceFragment  Fragment fragment     String backStateName    fragment getClass   getName      String fragmentTag   backStateName     FragmentManager manager   getSupportFragmentManager      boolean fragmentPopped   manager popBackStackImmediate  backStateName  0      if   fragmentPopped  amp  amp  manager findFragmentByTag fragmentTag     null     fragment not in back stack  create it      FragmentTransaction ft   manager beginTransaction        ft replace R id content frame  fragment  fragmentTag       ft setTransition FragmentTransaction TRANSIT FRAGMENT FADE       ft addToBackStack backStateName       ft commit             The conditional was changed a bit since selecting the same fragment while it was visible also caused duplicate entries   Implementation   I highly suggest not taking the the updated replaceFragment   method apart like you did in your code  All the logic is contained in this method and moving parts around may cause problems   This means you should copy the updated replaceFragment   method into your class then change  backStateName   fragmentName getClass   getName    fragmentPopped   manager popBackStackImmediate backStateName  0   if   fragmentPopped                ft replace R id content frame  fragmentName     ft setTransition FragmentTransaction TRANSIT FRAGMENT FADE   ft addToBackStack backStateName   ft commit      so it is simply  replaceFragment  fragmentName       EDIT  2  To update the drawer when the back stack changes  make a method that accepts in a Fragment and compares the class names  If anything matches  change the title and selection  Also add an OnBackStackChangedListener and have it call your update method if there is a valid Fragment   For example  in the Activity s onCreate    add  getSupportFragmentManager   addOnBackStackChangedListener new OnBackStackChangedListener         Override   public void onBackStackChanged         Fragment f   getSupportFragmentManager   findFragmentById R id content frame       if  f    null         updateTitleAndDrawer  f                    And the other method   private void updateTitleAndDrawer  Fragment fragment     String fragClassName   fragment getClass   getName       if  fragClassName equals A class getName          setTitle   A          set selected item position  etc       else if  fragClassName equals B class getName          setTitle   B          set selected item position  etc       else if  fragClassName equals C class getName          setTitle   C          set selected item position  etc         Now  whenever the back stack changes  the title and checked position will reflect the visible Fragment

[android] How to resume Fragment from BackStack if exists

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