How to resume existing Fragment from BackStack
Solution 1
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 && 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
.
Solution 2
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
Solution 3
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();
Solution 4
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();
}
}
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Updated on April 15, 2021Comments
-
Kaidul about 3 years
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 thenB
, the stack looks like this:| | |B| |C| |A| ___
And when I press the 'back' button,
B
is destroyed andC
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 thenB
, then press 'back',B
is removed andA
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
, thenB
, thenC
, thenB
again...Expected:
| | | | |B| |A| ___
Actual:
| | |B| |B| |A| ___
Should I override
onBackPressed()
with any customization or am I missing something? -
Kaidul almost 11 yearsThanks for your answer. :) It is working partially. I have edited my question with progress. Please take a look )
-
A--C almost 11 years@typedef I will make a sample project and see if I can reproduce your issue. I'll edit the question/leave a comment if I find anything useful.
-
A--C almost 11 years@typedef I edited the question. Make sure to follow all the instructions.
-
Kaidul almost 11 yearsHello Sir, this is working perfectly :) MY two problems gone! But in every successful Fragment replacement, I did update the window title by
setTitle(title[position]);
and changed the selected item of navigation drawer bymDrawerList.setItemChecked(position, true);
. This is not working now when I press back button and resume a fragment frombackstack
. The title and selected item in navigation drawer is not updated. Where I can place this update-code to make the update? -
Kaidul almost 11 yearsMay be I can update the title and selectedItem of navigation drawer in
onResume
of every fragment. But this will require to do more codes in every frgament. Is there any good way? -
A--C almost 11 years@typedef This edit was the first thing that came to mind. It's definitely a better way than using
onResume()
. -
Kaidul almost 11 yearsSir, one of my
fragment
is anested fragment
and it has three childs. Problem is - the parent fragment's view is overriding when I am resuming it frombackstack
. How can I avoid this? DO you encounter something like that before? -
A--C almost 11 years@typedef Unfortunately I haven't. Consider making a new question so other people can help as well.
-
Kaidul almost 11 yearscan I recreate the view of
fragment
during resume from backstack? -
A--C almost 11 years@typedef No, you cannot reinflate the
View
there. Make a new question, explain the problem in detail, and add any relevant code as well as screenshots. -
Kaidul almost 11 yearsthis is my new question link: stackoverflow.com/questions/18322020/…
-
Kaidul almost 11 yearsSir, one more help please! :( Can I maintain backStack for all fragments except one? I mean I need my one fragment not to include in the backstack. I tried but I can't be able to modify your code to fulfill my purpose. :(
-
Rishabh Srivastava over 10 yearsI want to know that which method of the previous fragment is called first when the current fragment is popped back?Actually I wanted to run a piece of code when the current fragment is paused n previous is opened.
-
A--C over 10 years@RishabhSrivastava keep in mind a "pop" usually destroys the topmost fragment. As to which method is called first, it depends - have a look at the Fragment Lifecycle. For your case, I'd use an
OnBackstackChangedListener
so that you can guarantee that you're dealing with the right Fragment. -
Rishabh Srivastava over 10 yearsi have got two fragments when some data is changed in the first and second is opened,the change is reflected in second and when I change the data in second and go back,i want the change to be reflected in the first,that's what is not happening.I went through fragment life cycle but no help as no method is called when current fragment is popped back.
-
A--C over 10 years@RishabhSrivastava Which is why I suggested the
OnBackstackChangedListener
as well. -
Alexander Farber over 8 yearsWhy compare class names - if you can use
instanceof
instead, on the Fragment returned byfindFragmentById
? -
A--C over 8 years@AlexanderFarber You're correct. Back when I made this answer I wasn't thinking about
instanceof
:) -
Zin Win Htet over 8 yearsDear Sir, Not Working here.. :'( It's still saying "Fragment already added".
-
albert over 8 yearsi am facing issue stackoverflow.com/questions/34652142/…
-
Leonid Ustenko almost 8 yearsWhy do you compare Fragment classes names instead of comparing instances like if (frag instanceof A) ... Is it somehow better?
-
Leonid Ustenko almost 8 yearsAnd what to do if in some cases I don't want to add fragment to the back stack? I could overload method like replaceFragment (Fragment fragment, boolean addToBackStack) { ... if (addToBackStack) { ft.addToBackStack(backStateName);} ... } But in this case I woun't be able to update action bar text in onBackStackChanged as it will not be called
-
erluxman over 7 yearsPlease let me know if answering like this is against the rules I just wanted to make it easy for people to see in this post. Thanks ..
-
Raeglan over 6 yearsYour solution sounds good, but if you have three fragments and click on them
A-B-C-B
and press back one time you'll be going back toA
and not back toC
. That is because thepopBackStackImmediate
not only pops the tag given but also everything above. Is there any work around there? -
Kathir over 5 yearsI am not sure whether it is against the rules (probably not), but this is definitely helpful
-
Rik van Velzen about 5 yearsWhat is the use of the third line? -> manager.findFragmentByTag ( tag ); Looks like it isn't doing anything..
-
Vivek Pratap Singh almost 5 years@X-Black...BaseFragment is a base class for every fragment used in the application.
-
July over 4 yearsPlease, how can I update some public parameters of the fragments (took from the backstack) before to make it visible? @A--C