Develop Reference

How to find the fragment in back stack and just show it in android

I have a Activity where I load 3 fragments one after another
FragmentA
FragmentB
FragmentC
Flow is Like this I have used Adding fragment one above another
Start-Activity -----> Load FragmentA ----> Load FragmentB ----> Load FragmentC
What I am trying to do now is:
Now assuming now FragmentC is the top fragment shown
I want to find the FragmentA from the stack and just show it instead of creating a fragmentA all over again
Code I have used to add fragmentA is for Example:
Fragment fragment = null;
FragmentTransaction fragmentTransaction = null;
fragment = new FragmentA();
fragmentTransaction = fragmentManager.beginTransaction();
fragmentTransaction.addToBackStack(FragmentA.class.getSimpleName());
fragmentTransaction.setCustomAnimations(android.R.anim.fade_in, android.R.anim.fade_out);
fragmentTransaction.add(R.id.container, fragment, FragmentA.class.getSimpleName());
if(fragment!=null && fragmentTransaction!=null){
fragmentTransaction.commitAllowingStateLoss();
}

Look at FragmentManager.getBackStackEntryAt method, from there you can go back to any fragment of your history…

Loop through the back stack entries, meanwhile, if you find any matching Fragment by id or tag, just pop back stack inclusive with fragment A's name/tag so that the fragment A is just displayed rather than adding once again.

The example code to retrieve a fragment by Tag would look like this
FragmentA frA = getSupportFragmentManager().findFragmentByTag(FragmentA.class.getSimpleName());
and if it's not null you can reuse it in your container
if(frA != null) {
FragmentTransaction fragmentTransaction = getSupportFragmentManager.beginTransaction();
fragmentTransaction.setCustomAnimations(android.R.anim.fade_in, android.R.anim.fade_out);
//you could add this transactionn to backstack again here if you want to be able to pop it later
fragmentTransaction.add(R.id.container, frA, FragmentA.class.getSimpleName());
} else {
//if your fragment is null as it was destroyed previously you can create a new one here
}

You are giving a tag, fragmentTransaction.addToBackStack(FragmentA.class.getSimpleName()); to the transaction , you can use the same tag to find the fragment in the backstack, before creating a new frgament, check the backstack for the fragment using findFragmentByTag on the fragment manager, if it exist, the method returns the fragment otherwise null

try it!
val fm: FragmentManager? = fragmentManager
for (entry in 0 until fm.getBackStackEntryCount()) {
Log.i(TAG, "Found fragment: " + fm.getBackStackEntryAt(entry).getId())
}

Android reload fragments stack on restore

I’m developing an android application that makes heavy use of fragments, I’m running into an issue and I’ve been unable to find a solution so far.
The flow is this: the app is launched and MainActivity is the first responder, now, depending on user interaction several fragments gets loaded and pushed onto the stack.
Here is an example:
Main Activity -> fragment A -> fragment B -> fragment C -> etc..
Back history is enabled like so:
fragment C -> fragment B -> fragment A -> etc..
Everything works perfectly fine as long as my application is in foreground but everything breaks when the application goes in background.
If I’m on fragment B for example and I press the home button the application goes in background and when I restore it back it starts from MainActivity with fragment A.
Also, the toolbar shows the title of fragment B and, since fragment A contains a recyclerview I can see parts of fragment B between item rows, like a background image.
This is how I load fragments:
public void loadFragment(Fragment fragment, Boolean addToStack) {
// Load fragment
FragmentManager fragmentManager = getSupportFragmentManager();
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
fragmentTransaction.replace(R.id.frame_container, fragment);
fragmentTransaction.addToBackStack(null);
// show back button
if (addToStack) {
// Code to show the back button.
}
else if (fragmentManager.getBackStackEntryCount() > 0 && !addToStack) {
hideBackButton();
fragmentManager.popBackStack(null, FragmentManager.POP_BACK_STACK_INCLUSIVE);
}
fragmentTransaction.commitAllowingStateLoss();
}
I call this function from MainActivity and from the fragments:
MyFragment theFragment = new MyFragment();
MainActivity.instance.loadFragment(theFragment, true);
What I want to achieve is that when the application is restored it gets straight to the previously loaded fragment, keeping the entire "back" history. How can I do this?
I'm not sure if other portions of code are needed, but if so I'll post them as required.

call the onResume() function:
public void onResume(){
Fragment frg = null;
frg = getSupportFragmentManager().findFragmentByTag("Your_Fragment_TAG");
final FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
ft.detach(frg);
ft.attach(frg);
ft.commit();
}

Ok so, after a lot of research I found the issue… and the issue was a mistake of mine.
I’d like to report it here for everyone that might run into the same issue.
At first I tried to force fragment replacement on onResume() function like so:
Fragment f = getSupportFragmentManager().findFragmentById(R.id.container);
FragmentManager fragmentManager = getSupportFragmentManager();
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
fragmentTransaction.replace(R.id.frame_container, f);
fragmentTransaction.addToBackStack(null);
However android should handle all of this automatically, at least in my knowledge, and so I tried to dig further and I finally narrowed it down to my onStart() method.
Basically I was registering the EventBus and making a function call
if (!EventBus.getDefault().isRegistered(this)) {
EventBus.getDefault().register(this);
UserNetworkManager userNetworkManager = new UserNetworkManager(MainActivity.mainActivity);
userNetworkManager.fetchFeed();
}
This code was creating the issue and after all it was not necessary to put it there, so I moved it to the onCreate() method, cleaned up my code a little bit and everything works fine now.

Nested fragment not getting removed completely

In my activity, I have various fragments. By default activity displays a map. On listitem click, Fragment A, B or C is displayed using following code:
protected void replaceFragment(int i) {
FragmentManager fragmentManager = getFragmentManager();
android.app.FragmentTransaction fragmentTransaction = fragmentManager
.beginTransaction();
switch (i) {
case FRAGMENT_A:
aFragment = new AFragment ();
fragmentTransaction.replace(R.id.main_framelayout_replace,
aFragment , TAG_A_FRAGMENT);
fragmentTransaction.commit();
break;//and so on.....
default:
break;
}
}
Here I'm facing an issue: When I replace Fragment A with Fragment B which is nested fragment i.e. it contains list and detail fragment within itself. When I try to remove any fragment other than Fragment B, I'm able to do it successfully and show the default map screen but when I'm on Frgament B and try to remove it, I'm not able to see default map screen. Instead a blank white screen is getting displayed.
Removing of fragments is done as follows:
if (aFragment != null) {
fragmentManager.beginTransaction()
.remove(aFragment ).commit();
}//and so on...
For fragment B which is having list and detailed fragment, I also do following in onDetach of fragment B,
fragmentManager.beginTransaction()
.remove(MainActivity.listFragment).commit();
Note: I'm not getting exception in any try catch. All the lines of code are getting executed without error including onDetach of Fragment B.
Am I doing anything wrong here? Any help appreciated.

Fragments and backstage sometimes get messed up

I have an activity with a container for fragments and a NavigationDrawer. If I select an item in the drawer, I call updatePage(index).
I also call updatePage(0) if I create the activity and the savedInstanceState == null to init my activity.
One fragment has a sub fragment and therefor it just replaces itself by the subfragment and adds the subfragment to the backstack, so that the user can navigate back to the previous fragment. In this fragment I call following code directly:
#Override
public void onClick(View view)
{
Event event = (Event)view.getTag();
FragmentManager fm = getActivity().getSupportFragmentManager();
GamesFragment f = new GamesFragment();
Bundle bundle = new Bundle();
bundle.putParcelable(GamesFragment.KEY_EVENT, event);
f.setArguments(bundle);
FragmentTransaction ft = fm.beginTransaction()
.replace(R.id.frame_container, f, f.getClass().getName())
.addToBackStack(null);
ft.commit();
}
Why does sometimes the removing of the old fragment not work? I get overlaying fragments, but only sometimes.
My activities updatePage function looks like following:
private void updatePage(int drawerSelection)
{
mDrawer.closeDrawer();
Fragment f = null;
FragmentManager fm = getSupportFragmentManager();
switch (drawerSelection)
{
case 0:
f = fm.findFragmentByTag(HomeFragment.class.getName());
if (f == null)
f = new HomeFragment();
break;
case 1:
f = fm.findFragmentByTag(EventFragment.class.getName());
if (f == null)
f = new EventFragment();
break;
default:
break;
}
if (f != null && !f.isAdded())
{
// SOLUTION:
// Backstack clearen
// fm.popBackStackImmediate(null, FragmentManager.POP_BACK_STACK_INCLUSIVE);
FragmentTransaction ft = fm.beginTransaction();
ft.replace(R.id.frame_container, f, f.getClass().getName());
ft.commit();
}
}

I saw such situation few times and I bet that it can happen after replacing with addToBackStack. Easiest fix is to add background to fragment layout. From android doc:
Note: When you remove or replace a fragment and add the transaction to the back stack, the fragment that is removed is stopped (not destroyed). If the user navigates back to restore the fragment, it restarts. If you do not add the transaction to the back stack, then the fragment is destroyed when removed or replaced.
This view is not redrawed entirely just overdrawed and if second fragment doesn't has background or view container redraw you will get effect as described. That's my theory :>. Sometimes Android documentation is not as clear as we would like it to be.

The problem is following use case:
Going to the EventFragment from the GameFragment pushes the "remove(EventFragment).add(GameFragment)" transaction to the backstack. If I now press the back button, this transaction will be undone and everything is fine. The backstack is empty again and everything works. BUT, if I don't press the back button, but change to another fragment through the menu, the backstack does still have the above mentioned transaction. Pressing back will now try to undo this transaction... It will just readd the EventFragment before the code in my menu click handler adds the fragment from the menu... This is how it could happen...
Easy solution, if I only want one backstack for every menu entry and want to delete the backstack, if I select another area of my app in the menu is, to clear the backstack before I go to another area through the menu...
So adding ' fm.popBackStackImmediate(null, FragmentManager.POP_BACK_STACK_INCLUSIVE);' before replacing the the current fragment will solve the problem (I added this solution as a comment to my main post)

Removing a Fragment from the back stack

I have a 3 fragments in an activity when the a tablet is held in portrait. However I only have 2 of these fragments when in landscape. The problem I am having is when going from portrait to landscape the activity is creating the 3rd fragment. I receive and error as this fragment cannot be created.
I have worked out that this fragment is being created because it is in the back stack.
I have tried to remove the fragment in the onDestroy method by using
FragmentTransaction f = fragmentManager.beginTransaction();
f.remove(mf);
f.commit();
However the I get an error saying that I cannot use this function after the onSaveInstanceState
What would be the correct way of taking this fragment out of the back stack?
Update
I should probably add that the fragment I am having problems with is a mapFragment from this libary
https://github.com/petedoyle/android-support-v4-googlemaps
The way I use it is like so
mf = MapFragment.newInstance(1, true);
ft = fragmentManager.beginTransaction();
ft.replace(R.id.mapContainer, mf);
ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_FADE);
ft.addToBackStack("map");
ft.commit();

You add to the back state from the FragmentTransaction and remove from the backstack using FragmentManager pop methods:
FragmentManager manager = getActivity().getSupportFragmentManager();
FragmentTransaction trans = manager.beginTransaction();
trans.remove(myFrag);
trans.commit();
manager.popBackStack();

I created a code to jump to the desired back stack index, it worked fine to my purpose.
ie. I have Fragment1, Fragment2 and Fragment3, I want to jump from Fragment3 to Fragment1
I created a method called onBackPressed in Fragment3 that jumps to Fragment1
Fragment3:
public void onBackPressed() {
FragmentManager fragmentManager = getFragmentManager();
fragmentManager.popBackStack(fragmentManager.getBackStackEntryAt(fragmentManager.getBackStackEntryCount()-2).getId(), FragmentManager.POP_BACK_STACK_INCLUSIVE);
}
In the activity, I need to know if my current fragment is the Fragment3, so I call the onBackPressed of my fragment instead calling super
FragmentActivity:
#Override
public void onBackPressed() {
Fragment f = getSupportFragmentManager().findFragmentById(R.id.my_fragment_container);
if (f instanceof Fragment3)
{
((Fragment3)f).onBackPressed();
} else {
super.onBackPressed();
}
}

you show fragment in a container (with id= fragmentcontainer) so you remove fragment with:
Fragment fragment = getSupportFragmentManager().findFragmentById(R.id.fragmentContainer);
fragmentTransaction.remove(fragment);
fragmentTransaction.addToBackStack(null);
fragmentTransaction.commit();

In case you ended up here trying to figure out how to remove fragment(s) from backstack and you are using Android Jetpack Navigation component you could just use app:popUpTo and app:popUpToInclusive in action node of navigation graph xml to specify fragments that you want to pop out of back stack.
https://developer.android.com/guide/navigation/navigation-navigate#pop
Check this too
https://stackoverflow.com/a/51974492/4594986

What happens if the fragment that you want to remove is not on top of the stack?
Then you can use theses functions
popBackStack(int arg0, int arg1);
popBackStack(String arg0, int arg1);