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how to use fragments backstack with shared element transition

shared element transition replace the fragment, so I can't add it to the backstack and call popbackstack when the back arrow button is pressed.
I have a main activity with inside a mainfragment, the main fragment handle a table layout so each tab is a fragment with inside a recycler view, when a recycler view element is clicked the shared element transition start to a new fragment that shows element details.
This is the adapter, where the element is clicked:
holder.image.setTransitionName("transition" + holder.getAdapterPosition());
if (fragment instanceof tab1_anime) {
((tab1_anime) fragment).openShowElementFragment(holder.getAdapterPosition(), v.findViewById(R.id.main_image));
}
This is the openShowElementFragment inside my tab fragment:
public void openShowElementFragment(int position, View view) {
AddElement element = anime_list.get(position);
ShowElementFragment showElementFragment = new ShowElementFragment();
Bundle bundle = new Bundle();
bundle.putString("transitionName", "transition" + position);
bundle.putSerializable("element", element);
bundle.putInt("position", position);
bundle.putInt("from", 0);
showElementFragment.setArguments(bundle);
((MainActivity) context).showFragmentWithTransition(this, showElementFragment, "showElementFragment", view, "transition" + position);
}
this is the openshowelementfragment function called in the previous code block:
public void showFragmentWithTransition(Fragment current, Fragment newFragment, String tag, View sharedView, String sharedElementName) {
FragmentManager fragmentManager = getSupportFragmentManager();
// check if the fragment is in back stack
boolean fragmentPopped = fragmentManager.popBackStackImmediate(tag, 0);
if (fragmentPopped) {
} else {
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
current.setSharedElementReturnTransition(TransitionInflater.from(this).inflateTransition(R.transition.default_transition));
current.setExitTransition(TransitionInflater.from(this).inflateTransition(R.transition.default_transition));
newFragment.setSharedElementEnterTransition(TransitionInflater.from(this).inflateTransition(R.transition.default_transition));
newFragment.setEnterTransition(TransitionInflater.from(this).inflateTransition(R.transition.default_transition));
}
fragmentManager.beginTransaction()
.replace(R.id.fragmentHolder, newFragment)
.addToBackStack(null)
.addSharedElement(sharedView, sharedElementName)
.commit();
}
}
and this is the backarrow button:
back_arrow.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
getSupportFragmentManager().popBackStack();
}
});
If I try to add the new fragment instead of replace the old one, then there is not animations at all.
If I try to replace the old fragment with the new one and using anyway the addtobackstack(null) then the shared element transition works from start to end BUT the fragment at the end is without data, empty:
I tried also:
getSupportFragmentManager()
.beginTransaction()
.replace(R.id.fragmentHolder, new MainFragment())
.addToBackStack(null)
.commit();
but in this way the shared element transition doesn't work on exit:

I think your problem is related to exit transition as you get solution of empty list, now for exit transition effect check below code.
public void showFragmentWithTransition(Fragment current, Fragment newFragment, String tag, View sharedView, String sharedElementName) {
FragmentManager fragmentManager = getSupportFragmentManager();
// check if the fragment is in back stack
boolean fragmentPopped = fragmentManager.popBackStackImmediate(tag, 0);
if (fragmentPopped) {
} else {
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
current.setSharedElementReturnTransition(TransitionInflater.from(this).inflateTransition(R.transition.default_transition));
current.setExitTransition(TransitionInflater.from(this).inflateTransition(R.transition.default_transition));
newFragment.setSharedElementEnterTransition(TransitionInflater.from(this).inflateTransition(R.transition.default_transition));
newFragment.setEnterTransition(TransitionInflater.from(this).inflateTransition(R.transition.default_transition));
newFragment.setExitTransition(TransitionInflater.from(this).inflateTransition(R.transition.default_transition));
newFragment.setSharedElementReturnTransition(TransitionInflater.from(this).inflateTransition(R.transition.default_transition));
}
getSupportFragmentManager().beginTransaction()
.addSharedElement(sharedElement, transitionName)
.replace(R.id.container, newFragment)
.addToBackStack(null)
.commit();
}
}
Here I add two new lines for exit transitions.
newFragment.setExitTransition(TransitionInflater.from(this).inflateTransition(R.transition.default_transition));
newFragment.setSharedElementReturnTransition(TransitionInflater.from(this).inflateTransition(R.transition.default_transition));
If its not work then follow below link, I think it will help you.
https://medium.com/#bherbst/fragment-transitions-with-shared-elements-7c7d71d31cbb

Your so called sharedElementName is actually a transitionName.
a) The reference example doesn't directly manipulate the backstack:
Android Fragment Transitions: RecyclerView to ViewPager & Blog.
b) Manual transactions might require another order of method calls:
getSupportFragmentManager().beginTransaction()
.addSharedElement(sharedElement, transitionName)
.replace(R.id.container, newFragment)
.addToBackStack(null)
.commit();
Also see this example, how alternate transitions could be be set, compared to:
TransitionInflater.from(this).inflateTransition(R.transition.default_transition)
Whatever R.transition.default_transition may be.
It may look strange when using the same transition for both ways, instead of enter/exit transitions, alike NavAction would feature. FragmentNavigator.Extras could be used to apply enter/exit transitions, when using navigation component; this also can be combined with ActionBar. Option a) is probably less complicated. b) something alike this Kotlin example might make more sense.
It's pointless to build clunky navigation FX when enter/exit transitions would be supported out-of-the-box. Maybe consider loading with Glide, when loading images.
Assume the following build.gradle; there's no need to reinvent the wheel.
dependencies {
androidTestImplementation "androidx.navigation:navigation-testing:2.5.3"
implementation 'androidx.navigation:navigation-runtime:2.5.3'
implementation 'androidx.navigation:navigation-fragment:2.5.3'
implementation 'androidx.navigation:navigation-ui:2.5.3'
annotationProcessor 'com.github.bumptech.glide:compiler:4.14.2'
implementation 'com.github.bumptech.glide:glide:4.14.2'
}
Then Navigation with FragmentNavigator.Extras might rather be the current method:
Bundle navArgs = new Bundle();
navArgs.putInt("position", position);
FragmentNavigator.Extras extras = new FragmentNavigator.Extras.Builder()
.addSharedElement(sharedElement, transitionName)
.build();
Navigation.findNavController(view).navigate(
R.id.details, // ID of Nav destination
navArgs, // Bundle of args
null, // NavOptions
extras);
One can also define transitionName in XML <action/> nodes.

Show hidden Fragment

I understand there were a lot of such issues. But a strange situation is happening with my option. Well, it’s not very clear. You can tell what is wrong.
I hide activeFragment if it is not null. Then I add a Fragment if it is not. And if there is, then I show. From the first time, everything works fine when I create it using the add() method or replace(). But if I go back and try to show() the already hidden Fragment, then it's just a white screen, there is no Fragment. What could be the problem?
private void loadFragment(Fragment fragment, String tag) {
if (fragment != null) {
FragmentManager fm = getSupportFragmentManager();
FragmentTransaction transaction = fm.beginTransaction();
if (activeFragment != null) {
transaction.hide(activeFragment);
}
if (fm.findFragmentByTag(tag) == null) {
transaction.add(R.id.fragment_container, fragment, tag);
} else {
transaction.show(fragment);
}
activeFragment = fragment;
transaction.commit();
}
}

How to run the same fragment several times?

I'm creating an app that will allow the user to take little tests. There is therefore a TestActivity made up by a PreTestFragment (with a button "Start Test"), a TestFragment and a PostTestFragment (with results of the test). As TestFragment will be the fragment hosting a single question I want it to be displayed several times (let's say 10).
All I could come up with was making a static counter that is incremented every time the user presses NEXT in a TestFragment and that makes him quit after the counter reached 10.
I'm new to fragment management, so I feel like I may have done several errors in the implementation of the onClick() of the NEXT button.
static private int current_question;
public void onClick(View view) {
FragmentManager mng = getFragmentManager();
FragmentTransaction fgmTr = mng.beginTransaction();
Fragment currentFgm = mng.findFragmentByTag(FragmentTags.TEST_FTAG.toString());
Fragment nextFgm;
Bundle bundle = currentFgm.getArguments();
if (current_question < 10) { // test still running
current_question++;
nextFgm = mng.findFragmentByTag(FragmentTags.TEST_FTAG.toString());
// ...
// putting needed data in the bundle
// ...
if (nextFgm == null)
nextFgm = new TestFragment();
} else { // test is finished
nextFgm = mng.findFragmentByTag(FragmentTags.POST_FTAG.toString());
// ...
// putting different needed data in the bundle
// ...
if (nextFgm == null)
nextFgm = new PostTestFragment();
}
nextFgm.setArguments(bundle);
fgmTr.replace(R.id.test_body, nextFgm, FragmentTags.POST_FTAG.toString());
fgmTr.addToBackStack(null);
fgmTr.commit();
}
#Override
public void setArguments(Bundle args) {
super.setArguments(args);
// Should I use if-else here too to pass different data in the bundle?
}
Running it and pressing "NEXT" the first time I get the following error:
java.lang.IllegalStateException: Fragment already active
How to fix this code?

If your fragment (nextFgm) has already been created, you can't call setArguments.
take a look:
https://developer.android.com/reference/android/app/Fragment.html#setArguments%28android.os.Bundle%29

Usually i did it by create a new fragment's instance every time:
android.support.v4.app.FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
fragmentTransaction.replace(R.id.frame, new myFragment);
fragmentTransaction.addToBackStack(null);
fragmentTransaction.commit();

Fragment listview update from activity

I am pretty new to Android (3 days), but I have a pretty good background in PHP (which may be the cause of my confusion in a Java based environment). I started building an Android app using Android Studio (Beta). I created the default Android Studio activity with the Navigation Drawer Activity. I edited the activity fragment part to look like this:
#Override
public void onNavigationDrawerItemSelected(int position) {
Bundle bundle = new Bundle();
bundle.putStringArrayList("contacts", arr);
bundle.putStringArrayList("messages", messages);
Fragment fragment = null;
switch (position) {
case 0:
fragment = new FriendsFragment();
break;
case 1:
fragment = new ChatsFragment();
break;
case 2:
fragment = new GroupsFragment();
break;
case 3:
fragment = new LogoutFragment();
break;
default:
break;
}
if (fragment != null) {
fragment.setArguments(bundle);
FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager.beginTransaction()
.replace(R.id.container, fragment).addToBackStack(null).commit();
}
}
As you can see I am passing a Bundle to my Fragments called "messages" and "contacts" when an item is selected in the Navigation Drawer. The "messages" bundle are XMPP messages received by the aSmack library from an OpenFire server. So basically I'm trying to create a XMPP client. When I run the app I can receive the messages in the "ChatsFragment".
Now my problem:
I have to press the "ChatsFragment" item on the drawer to have my messages updated (re-receive the bundle) everytime I feel like there are new messages received from the server. But I want this to be done automatically by the fragment.
First I would like to know if my procedure is correct (Activity listens to server, creates bundle, send bundle to fragment, bundle updates messages on receive**)
** = This part I haven't been able to understand how to implement.
1- If the procedure is correct tell me how I should get the messages to be updated by the fragment through the activity?
2- If this is not the correct way to do things in Android, recommend me a way of doing it.
My code for displaying the messages in fragment:
private void displayListView() {
// Messages array list
List<String> contacts = getArguments().getStringArrayList("messages");
//System.out.println("arr: " + contacts);
//create an ArrayAdaptar from the String Array
ArrayAdapter<String> dataAdapter = new ArrayAdapter<String>(getActivity(),
R.layout.url_list, contacts);
ListView listView = (ListView) getView().findViewById(R.id.listView);
// Assign adapter to ListView
listView.setAdapter(dataAdapter);
//enables filtering for the contents of the given ListView
listView.setTextFilterEnabled(true);
listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
public void onItemClick(AdapterView<?> parent, View view,
int position, long id) {
// Send the URL to the host activity
//mListener.onURLSelected(((TextView) view).getText().toString());
}
});
}
Thanks in advance.

Typically for long running operations in the background, like listening to a server, incoming messages, etc, you need to use Services. You do so by subclassing the Service class in Android.
Now for your problem - the design approach should be that you have a background service listening to incoming messages. Anytime a message is received (an input stream in your socket operator) you should send a "broadcast" an intent that a message was received. A custom broadcast receiver that you create should wait for this broadcast. Within the onReceive() method of this receiver, you should trigger the creation of the bundle and updating your message.
Remember you should always delegate your long running operations in Android to services. That is exactly what they are for.

So basically if you're already listening for new messages to come in your activity, then you must have some kind of callback like onMessageRecieved() or something like that.
If you do, you can then notify your fragment in this way.
Create a field (goes under your class declaration) called curFrag, so something like this:
public class MyActivity extends Activity {
private Fragment curFrag;
//other code...
}
then in the code you posted you would initialize the curFrag there, but you also need to set a tag for the current fragment. This will be based on your case statement. Make some final string variables as tags.
i.e.
public static final String CHATSTAG = "chatstag";
#Override
public void onNavigationDrawerItemSelected(int position) {
Bundle bundle = new Bundle();
bundle.putStringArrayList("contacts", arr);
bundle.putStringArrayList("messages", messages);
Fragment fragment = null;
String tag = null;
switch (position) {
case 0:
tag = FRIENDSTAG;
fragment = new FriendsFragment();
break;
case 1:
tag = CHATSTAG;... and so on through the switch statement.
fragment = new ChatsFragment();
break;
case 2:
fragment = new GroupsFragment();
break;
case 3:
fragment = new LogoutFragment();
break;
default:
break;
}
if (fragment != null) {
fragment.setArguments(bundle);
FragmentManager fragmentManager = getSupportFragmentManager();
//remember to set the tag.
if(tag != null) {
fragmentManager.beginTransaction()
.replace(R.id.container, fragment, tag).addToBackStack(null).commit();
} else {
fragmentManager.beginTransaction()
.replace(R.id.container,fragment,DEFAULTTAG).addToBackStack(null).commit();
}
//new code
curFrag = fragment;
}
}
Now in your activity when a new message comes in, check the tag of the fragment and then if it matches a certain fragment, notify the fragment that new data has come in and retrieve it in the fragment.
public void onMessageRecieved() {
if(curFrag.getTag().equalsIgnoreCase(CHATSTAG)) {
ChatsFragment frag = (ChatsFragment) curFrag;
frag.notifyDataRecieved();
}
}
Once you have a reference to your fragment in the activity, you have access to any public methods in that fragment.
If your fragment cannot access the data on its own, then you'll need to get a reference to the activity and create a method in the activity that returns the new data.
So in your activity:
public String getMessageData() {
String newData = ...//get stuff from server;
return newData;
}
then in your fragment
public void notifyNewMessage() {
try {
MyActivity activity = (MyActivity) getActivity();
} catch (ClassCastException e) {
e.printStackTrace();
} catch (NullPointerException e) {
e.printStackTrace();
}
String message = activity.getMessageData();
//do something with the message.
}
It's not necessarily pretty but it works pretty well. You should also check to make sure your fragments are attached when you do this so that you avoid null exceptions.
Hope this helps!

Calling a method on an object without knowing its class type

I'm using Fragment in my android app. At the moment I have 2 fragments being displayed in split view style, lets call the Fragment A and Fragment B. Fragment B gets changed frequently and there are many different types of Fragment it could get changed to.
I'm looking to call a method on Fragment B. This method exists in most but not all of the types of Fragments that could be displayed.
Here is what I have:
FragmentManager fm = getSupportFragmentManager();
Fragment frag = fm.findFragmentByTag("ContentFrag");
if (frag != null) {
if (frag.getClass().equals(ExampleFragment1.class))
((ExampleFragment1)frag).refresh();
else if (frag.getClass().equals(ExampleFragment2.class))
((ExampleFragment2)frag).refresh();
else if (frag.getClass().equals(ExampleFragment3.class))
((ExampleFragment3)frag).refresh();
}
And here is what I would like:
FragmentManager fm = getSupportFragmentManager();
Fragment frag = fm.findFragmentByTag("ContentFrag");
if (frag != null) {
frag.refresh();
}
Is there any way of achieving this or will I have to write a load of if statements?
Thanks

You can make your Fragments implement for example a Refreshable interface and you can check for it.
if(frag instanceof Refreshable)
((Refreshable)frag).refresh();
}
This is not pretty but prettier than the above code.

you could potentially use instanceof keyword to see if the fragment is an instance of one of these special fragments. Is this method that's only in some fragments something you made yourself or part of the API?
If it's one you made yourself have those fragments implement an interface called something like RefreshableFragment. This interface would contain said method, then all you have to do is:
if(frag!=null && frag instanceof RefreshableFragment)
frag.refresh();

the solution is to create a parent class named RefreshableFragment, that has refresh() method:
public class RefreshableFragment extends Fragment {
public void refresh();
}
all your fragment classes should extend this class:
public class ExampleFragment1 extends RefreshableFragment {
public void refresh() {
// implementation
}
}
then you can use the refreshed fragment in your code:
FragmentManager fm = getSupportFragmentManager();
RefreshableFragment frag = (RefreshableFragment)fm.findFragmentByTag("ContentFrag");
if (frag != null) {
frag.refresh();
}