Develop Reference

Android-Save state of Fragment with RecyclerView [duplicate]

I've written up a dummy activity that switches between two fragments. When you go from FragmentA to FragmentB, FragmentA gets added to the back stack. However, when I return to FragmentA (by pressing back), a totally new FragmentA is created and the state it was in is lost. I get the feeling I'm after the same thing as this question, but I've included a complete code sample to help root out the issue:
public class FooActivity extends Activity {
#Override public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
final FragmentTransaction transaction = getFragmentManager().beginTransaction();
transaction.replace(android.R.id.content, new FragmentA());
transaction.commit();
}
public void nextFragment() {
final FragmentTransaction transaction = getFragmentManager().beginTransaction();
transaction.replace(android.R.id.content, new FragmentB());
transaction.addToBackStack(null);
transaction.commit();
}
public static class FragmentA extends Fragment {
#Override public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
final View main = inflater.inflate(R.layout.main, container, false);
main.findViewById(R.id.next_fragment_button).setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
((FooActivity) getActivity()).nextFragment();
}
});
return main;
}
#Override public void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
// Save some state!
}
}
public static class FragmentB extends Fragment {
#Override public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
return inflater.inflate(R.layout.b, container, false);
}
}
}
With some log messages added:
07-05 14:28:59.722 D/OMG ( 1260): FooActivity.onCreate
07-05 14:28:59.742 D/OMG ( 1260): FragmentA.onCreateView
07-05 14:28:59.742 D/OMG ( 1260): FooActivity.onResume
<Tap Button on FragmentA>
07-05 14:29:12.842 D/OMG ( 1260): FooActivity.nextFragment
07-05 14:29:12.852 D/OMG ( 1260): FragmentB.onCreateView
<Tap 'Back'>
07-05 14:29:16.792 D/OMG ( 1260): FragmentA.onCreateView
It's never calling FragmentA.onSaveInstanceState and it creates a new FragmentA when you hit back. However, if I'm on FragmentA and I lock the screen, FragmentA.onSaveInstanceState does get called. So weird...am I wrong in expecting a fragment added to the back stack to not need re-creation? Here's what the docs say:
Whereas, if you do call addToBackStack() when removing a fragment,
then the fragment is stopped and will be resumed if the user navigates
back.

If you return to a fragment from the back stack it does not re-create the fragment but re-uses the same instance and starts with onCreateView() in the fragment lifecycle, see Fragment lifecycle.
So if you want to store state you should use instance variables and not rely on onSaveInstanceState().

Comparing to Apple's UINavigationController and UIViewController, Google does not do well in Android software architecture. And Android's document about Fragment does not help much.
When you enter FragmentB from FragmentA, the existing FragmentA instance is not destroyed. When you press Back in FragmentB and return to FragmentA, we don't create a new FragmentA instance. The existing FragmentA instance's onCreateView() will be called.
The key thing is we should not inflate view again in FragmentA's onCreateView(), because we are using the existing FragmentA's instance. We need to save and reuse the rootView.
The following code works well. It does not only keep fragment state, but also reduces the RAM and CPU load (because we only inflate layout if necessary). I can't believe Google's sample code and document never mention it but always inflate layout.
Version 1(Don't use version 1. Use version 2)
public class FragmentA extends Fragment {
View _rootView;
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
if (_rootView == null) {
// Inflate the layout for this fragment
_rootView = inflater.inflate(R.layout.fragment_a, container, false);
// Find and setup subviews
_listView = (ListView)_rootView.findViewById(R.id.listView);
...
} else {
// Do not inflate the layout again.
// The returned View of onCreateView will be added into the fragment.
// However it is not allowed to be added twice even if the parent is same.
// So we must remove _rootView from the existing parent view group
// (it will be added back).
((ViewGroup)_rootView.getParent()).removeView(_rootView);
}
return _rootView;
}
}
------Update on May 3 2005:-------
As the comments mentioned, sometimes _rootView.getParent() is null in onCreateView, which causes the crash. Version 2 removes _rootView in onDestroyView(), as dell116 suggested. Tested on Android 4.0.3, 4.4.4, 5.1.0.
Version 2
public class FragmentA extends Fragment {
View _rootView;
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
if (_rootView == null) {
// Inflate the layout for this fragment
_rootView = inflater.inflate(R.layout.fragment_a, container, false);
// Find and setup subviews
_listView = (ListView)_rootView.findViewById(R.id.listView);
...
} else {
// Do not inflate the layout again.
// The returned View of onCreateView will be added into the fragment.
// However it is not allowed to be added twice even if the parent is same.
// So we must remove _rootView from the existing parent view group
// in onDestroyView() (it will be added back).
}
return _rootView;
}
#Override
public void onDestroyView() {
if (_rootView.getParent() != null) {
((ViewGroup)_rootView.getParent()).removeView(_rootView);
}
super.onDestroyView();
}
}
WARNING!!!
This is a HACK! Though I am using it in my app, you need to test and read comments carefully.

I guess there is an alternative way to achieve what you are looking for.
I don't say its a complete solution but it served the purpose in my case.
What I did is instead of replacing the fragment I just added target fragment.
So basically you will be going to use add() method instead replace().
What else I did.
I hide my current fragment and also add it to backstack.
Hence it overlaps new fragment over the current fragment without destroying its view.(check that its onDestroyView() method is not being called. Plus adding it to backstate gives me the advantage of resuming the fragment.
Here is the code :
Fragment fragment=new DestinationFragment();
FragmentManager fragmentManager = getFragmentManager();
android.app.FragmentTransaction ft=fragmentManager.beginTransaction();
ft.add(R.id.content_frame, fragment);
ft.hide(SourceFragment.this);
ft.addToBackStack(SourceFragment.class.getName());
ft.commit();
AFAIK System only calls onCreateView() if the view is destroyed or not created.
But here we have saved the view by not removing it from memory. So it will not create a new view.
And when you get back from Destination Fragment it will pop the last FragmentTransaction removing top fragment which will make the topmost(SourceFragment's) view to appear over the screen.
COMMENT: As I said it is not a complete solution as it doesn't remove the view of Source fragment and hence occupying more memory than usual. But still, serve the purpose. Also, we are using a totally different mechanism of hiding view instead of replacing it which is non traditional.
So it's not really for how you maintain the state, but for how you maintain the view.

I would suggest a very simple solution.
Take the View reference variable and set view in OnCreateView. Check if view already exists in this variable, then return same view.
private View fragmentView;
public View onCreateView(LayoutInflater inflater, #Nullable ViewGroup container, #Nullable Bundle savedInstanceState) {
super.onCreateView(inflater, container, savedInstanceState);
if (fragmentView != null) {
return fragmentView;
}
View view = inflater.inflate(R.layout.yourfragment, container, false);
fragmentView = view;
return view;
}

I came across this problem in a Fragment containing a map, which has too many setup details to save/reload.
My solution was to basically keep this Fragment active the whole time (similar to what #kaushal mentioned).
Say you have current Fragment A and wants to display Fragment B.
Summarizing the consequences:
replace() - remove Fragment A and replace it with Fragment B. Fragment A will be recreated once brought to the front again
add() - (create and) add a Fragment B and it overlap Fragment A, which is still active in the background
remove() - can be used to remove Fragment B and return to A. Fragment B will be recreated when called later on
Hence, if you want to keep both Fragments "saved", just toggle them using hide()/show().
Pros: easy and simple method to keep multiple Fragments running
Cons: you use a lot more memory to keep all of them running. May run into problems, e.g. displaying many large bitmaps

onSaveInstanceState() is only called if there is configuration change.
Since changing from one fragment to another there is no configuration change so no call to onSaveInstanceState() is there. What state is not being save? Can you specify?
If you enter some text in EditText it will be saved automatically. Any UI item without any ID is the item whose view state shall not be saved.

first: just use add method instead of replace method of FragmentTransaction class then you have to add secondFragment to stack by addToBackStack method
second :on back click you have to call popBackStackImmediate()
Fragment sourceFragment = new SourceFragment ();
final Fragment secondFragment = new SecondFragment();
final FragmentTransaction ft = getChildFragmentManager().beginTransaction();
ft.add(R.id.child_fragment_container, secondFragment );
ft.hide(sourceFragment );
ft.addToBackStack(NewsShow.class.getName());
ft.commit();
((SecondFragment)secondFragment).backFragmentInstanceClick = new SecondFragment.backFragmentNewsResult()
{
#Override
public void backFragmentNewsResult()
{
getChildFragmentManager().popBackStackImmediate();
}
};

Kotlin and ViewBinding Solution
I am using replace() and backstack() method for FragmentTransaction. The problem is that the backstack() method calls the onCreateView of the Previous Fragment which causes in re-built of Fragment UI. Here is a solution for that:
private lateinit var binding: FragmentAdRelevantDetailsBinding
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,savedInstanceState: Bundle?
): View {
if (!this::binding.isInitialized)
binding = FragmentAdRelevantDetailsBinding.inflate(layoutInflater, container, false)
return binding.root
}

Here, since onSaveInstanceState in fragment does not call when you add fragment into backstack. The fragment lifecycle in backstack when restored start onCreateView and end onDestroyView while onSaveInstanceState is called between onDestroyView and onDestroy. My solution is create instance variable and init in onCreate. Sample code:
private boolean isDataLoading = true;
private ArrayList<String> listData;
public void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
isDataLoading = false;
// init list at once when create fragment
listData = new ArrayList();
}
And check it in onActivityCreated:
public void onViewCreated(View view, #Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
if(isDataLoading){
fetchData();
}else{
//get saved instance variable listData()
}
}
private void fetchData(){
// do fetch data into listData
}

getSupportFragmentManager().addOnBackStackChangedListener(new FragmentManager.OnBackStackChangedListener()
{
#Override
public void onBackStackChanged()
{
if (getSupportFragmentManager().getBackStackEntryCount() == 0)
{
//setToolbarTitle("Main Activity");
}
else
{
Log.e("fragment_replace11111", "replace");
}
}
});
YourActivity.java
#Override
public void onBackPressed()
{
Fragment fragment = getSupportFragmentManager().findFragmentById(R.id.Fragment_content);
if (fragment instanceof YourFragmentName)
{
fragmentReplace(new HomeFragment(),"Home Fragment");
txt_toolbar_title.setText("Your Fragment");
}
else{
super.onBackPressed();
}
}
public void fragmentReplace(Fragment fragment, String fragment_name)
{
try
{
fragmentTransaction = fragmentManager.beginTransaction();
fragmentTransaction.replace(R.id.Fragment_content, fragment, fragment_name);
fragmentTransaction.setCustomAnimations(R.anim.enter_from_right, R.anim.exit_to_left, R.anim.enter_from_left, R.anim.exit_to_right);
fragmentTransaction.addToBackStack(fragment_name);
fragmentTransaction.commitAllowingStateLoss();
}
catch (Exception e)
{
e.printStackTrace();
}
}

My problem was similar but I overcame me without keeping the fragment alive. Suppose you have an activity that has 2 fragments - F1 and F2. F1 is started initially and lets say in contains some user info and then upon some condition F2 pops on asking user to fill in additional attribute - their phone number. Next, you want that phone number to pop back to F1 and complete signup but you realize all previous user info is lost and you don't have their previous data. The fragment is recreated from scratch and even if you saved this information in onSaveInstanceState the bundle comes back null in onActivityCreated.
Solution:
Save required information as an instance variable in calling activity. Then pass that instance variable into your fragment.
#Override
public void onActivityCreated(#Nullable Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
Bundle args = getArguments();
// this will be null the first time F1 is created.
// it will be populated once you replace fragment and provide bundle data
if (args != null) {
if (args.get("your_info") != null) {
// do what you want with restored information
}
}
}
So following on with my example: before I display F2 I save user data in the instance variable using a callback. Then I start F2, user fills in phone number and presses save. I use another callback in activity, collect this information and replace my fragment F1, this time it has bundle data that I can use.
#Override
public void onPhoneAdded(String phone) {
//replace fragment
F1 f1 = new F1 ();
Bundle args = new Bundle();
yourInfo.setPhone(phone);
args.putSerializable("you_info", yourInfo);
f1.setArguments(args);
getFragmentManager().beginTransaction()
.replace(R.id.fragmentContainer, f1).addToBackStack(null).commit();
}
}
More information about callbacks can be found here: https://developer.android.com/training/basics/fragments/communicating.html

Replace a Fragment using following code:
Fragment fragment = new AddPaymentFragment();
getSupportFragmentManager().beginTransaction().replace(R.id.frame, fragment, "Tag_AddPayment")
.addToBackStack("Tag_AddPayment")
.commit();
Activity's onBackPressed() is :
#Override
public void onBackPressed() {
android.support.v4.app.FragmentManager fm = getSupportFragmentManager();
if (fm.getBackStackEntryCount() > 1) {
fm.popBackStack();
} else {
finish();
}
Log.e("popping BACKSTRACK===> ",""+fm.getBackStackEntryCount());
}

Public void replaceFragment(Fragment mFragment, int id, String tag, boolean addToStack) {
FragmentTransaction mTransaction = getSupportFragmentManager().beginTransaction();
mTransaction.replace(id, mFragment);
hideKeyboard();
if (addToStack) {
mTransaction.addToBackStack(tag);
}
mTransaction.commitAllowingStateLoss();
}
replaceFragment(new Splash_Fragment(), R.id.container, null, false);

Perfect solution that find old fragment in stack and load it if exist in stack.
/**
* replace or add fragment to the container
*
* #param fragment pass android.support.v4.app.Fragment
* #param bundle pass your extra bundle if any
* #param popBackStack if true it will clear back stack
* #param findInStack if true it will load old fragment if found
*/
public void replaceFragment(Fragment fragment, #Nullable Bundle bundle, boolean popBackStack, boolean findInStack) {
FragmentManager fm = getSupportFragmentManager();
FragmentTransaction ft = fm.beginTransaction();
String tag = fragment.getClass().getName();
Fragment parentFragment;
if (findInStack && fm.findFragmentByTag(tag) != null) {
parentFragment = fm.findFragmentByTag(tag);
} else {
parentFragment = fragment;
}
// if user passes the #bundle in not null, then can be added to the fragment
if (bundle != null)
parentFragment.setArguments(bundle);
else parentFragment.setArguments(null);
// this is for the very first fragment not to be added into the back stack.
if (popBackStack) {
fm.popBackStack(null, FragmentManager.POP_BACK_STACK_INCLUSIVE);
} else {
ft.addToBackStack(parentFragment.getClass().getName() + "");
}
ft.replace(R.id.contenedor_principal, parentFragment, tag);
ft.commit();
fm.executePendingTransactions();
}
use it like
Fragment f = new YourFragment();
replaceFragment(f, null, boolean true, true);

Calling the Fragment lifecycle methods properly and using onSavedInstanceState() can solve the problem.
i.e Call onCreate(), onCreateView(), onViewCreated() and onSavedInstanceState() properly and save Bundle in onSaveInstanceState() and resotre it in onCreate() method.
I don't know how but it worked for me without any error.
If anyone can explain it will very much appreciated.
public class DiagnosisFragment extends Fragment {
private static final String TITLE = "TITLE";
private String mTitle;
private List mList = null;
private ListAdapter adapter;
public DiagnosisFragment(){}
public DiagnosisFragment(List list, String title){
mList = list;
mTitle = title;
}
#Override
public void onCreate(#Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if(savedInstanceState != null){
mList = savedInstanceState.getParcelableArrayList(HEALTH_ITEMS);
mTitle = savedInstanceState.getString(TITLE);
itemId = savedInstanceState.getInt(ID);
mChoiceMode = savedInstanceState.getInt(CHOICE_MODE);
}
getActivity().setTitle(mTitle);
adapter = (ListAdapter) new HealthAdapter(mList, getContext()).load(itemId);
}
#Nullable
#Override
public View onCreateView(#NonNull LayoutInflater inflater, #Nullable ViewGroup container, #Nullable Bundle savedInstanceState) {
return inflater.inflate(R.layout.diagnosis_fragment, container, false);
}
#Override
public void onViewCreated(#NonNull View view, #Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
ListView lv = view.findViewById(R.id.subLocationsSymptomsList);
lv.setAdapter(adapter);
}
#Override
public void onSaveInstanceState(#NonNull Bundle outState) {
outState.putParcelableArrayList(HEALTH_ITEMS, (ArrayList) mList);
outState.putString(TITLE, mTitle);
}
}

For who has looking for solution :
#Override
public void onDestroyView() {
Bundle savedState=new Bundle();
// put your data in bundle
// if you have object and want to restore you can use gson to convert it
//to sring
if (yourObject!=null){
savedState.putString("your_object_key",new Gson().toJson(yourObject));
}
if (getArguments()==null){
setArguments(new Bundle());
}
getArguments().putBundle("saved_state",savedState);
super.onDestroyView();
}
and in onViewCreated() method :
Bundle savedState=null;
if (getArguments()!=null){
savedState=getArguments().getBundle("saved_state");
}
if (savedState!=null){
// set your restored data to your view
}

Fragment BackStack lifecycle issues

I have a fragment activity, which has a fragment A. Fragment A does some important things in onViewCreated method:
#Override
public void onViewCreated(#NonNull View view, #Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
mission1 = view.findViewById(R.id.mission1);
mission2 = view.findViewById(R.id.mission2);
mission3a = view.findViewById(R.id.mission3a);
mission3b = view.findViewById(R.id.mission3b);
imageButtonList.add(mission1);
imageButtonList.add(mission2);
imageButtonList.add(mission3a);
imageButtonList.add(mission3b);
prepareButtons();
}
OK, now, this fragment A, has a button which creates a new fragment B, but I want to add a "back" button in the new Fragment B, so I added fragment A into backstack when launching Fragment B:
FragmentTransaction ft = getActivity().getSupportFragmentManager().beginTransaction();
CampaignMissionFragment fragment = CampaignMissionFragment.newInstance(auxMission);
ft.replace(R.id.fragmentContainer, fragment);
ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_FADE);
ft.addToBackStack(null);
ft.commit();
And in Fragment B, I added this to back button onClick():
getFragmentManager().popBackStack();
The problem is that when I press back on Fragment B, onViewCreated method of Fragment A is being called, so my imageButtonList array is getting a wrong amount of buttons inside because of the same buttons are being inserted again.
What would be the correct way to solve this issue? I thought that Fragment had similar behavior to Activities, where you can solve this issue putting the code that you don't want to execute two times in onCreate. But in this case, I can't do that because my views are not available in onCreate method of the fragment.

You may try to clear the imageButtonList in onDestroyView,
Another solution would be to check if savedInstanceState is not null and then avoid adding the button to the list if this is the case
Also, no View related operation in onCreate()

Update your fragment activity's onBackPressed as -
#Override
public void onBackPressed() {
FragmentManager fm = getFragmentManager();
if (fm.getBackStackEntryCount() > 0) {
fm.popBackStack();
} else {
super.onBackPressed();
}
}

Check the savedInstanceState object to determine if this is the first time the Fragment is being initialized and only save your fields if it's the first time through:
#Override
public void onViewCreated(#NonNull View view, #Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
mission1 = view.findViewById(R.id.mission1);
mission2 = view.findViewById(R.id.mission2);
mission3a = view.findViewById(R.id.mission3a);
mission3b = view.findViewById(R.id.mission3b);
if (savedInstanceState == null) {
imageButtonList.add(mission1);
imageButtonList.add(mission2);
imageButtonList.add(mission3a);
imageButtonList.add(mission3b);
prepareButtons();
}
}

Try to Write Code in OneResume
#Override
public void onResume() {
mission1 = view.findViewById(R.id.mission1);
mission2 = view.findViewById(R.id.mission2);
mission3a = view.findViewById(R.id.mission3a);
mission3b = view.findViewById(R.id.mission3b);
imageButtonList.add(mission1);
imageButtonList.add(mission2);
imageButtonList.add(mission3a);
imageButtonList.add(mission3b);
prepareButtons();
}

how to save android recycler view state (scroll position) in an activity with two fragments

I am new to Android and, as a first step, am building an app, for running in a handset, with an activity in which I put two fragments. The first fragment has a recycler view of items that are supposed to represent article titles. When I click on one, the second fragment opens and shows the title (in a text view) and the content (in another text view) of the article (for the moment, for simplicity, I put the article title as fake titles and I have a setting for which the content is not shown but it is shown the title in the content text view too).
I want to save the scroll position of the recycler view.
When I scroll down, having on top of the screen an article title different from the first, I choose an article and my second fragment opens with the expected contents, and that's ok. When I rotate to landscape, the same fragment contains the same content, ok. So:
1) when I press the back button from the landscape, returning to the first fragment, I get the same setting for the recycler view, ok;
2) when I rotate again to portrait, remaining on the second fragment, it is ok too. Now, if I press the back button to return to the first fragment, to the list of articles, the recycler view is NOT set to start with the item I initially scrolled to. What can I do?
I have this code in the first fragment, the one containing the recycler view:
#Override
public void onSaveInstanceState(Bundle state) {
int lastFirstVisiblePosition = ((LinearLayoutManager) recyclerView.getLayoutManager()).findFirstCompletelyVisibleItemPosition();
state.putInt(Articles.RECYCLER_POSITION_KEY, lastFirstVisiblePosition);
super.onSaveInstanceState(state);
}
#Override
public void onActivityCreated(Bundle state) {
super.onActivityCreated(state);
if (state != null) {
int lastFirstVisiblePosition = state.getInt(Articles.RECYCLER_POSITION_KEY);
((LinearLayoutManager) recyclerView.getLayoutManager()).scrollToPosition(lastFirstVisiblePosition);
}
}
What am I missing? Thanks.
[EDIT] In my listener is this, for invoking the second fragment:
ArticleReaderFrag newFragment = new ArticleReaderFrag();
Bundle args = new Bundle();
args.putString(NEW_FRAG_TITLE_KEY, item);
args.putString(NEW_FRAG_BODY_KEY, itemb);
newFragment.setArguments(args);
FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
transaction.replace(R.id.main_activity, newFragment);
transaction.addToBackStack(null);
transaction.commit();

Reuse Fragment
When the Activity launches for the first time create a new instance of Fragment and use a TAG to save it with FragmentManager. When the activity gets recreated after orientation change. Retreive the old instance using the Tag.
Here is a sample code which you should have in your activity.
#Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.first_activity);
fragmentManager = getSupportFragmentManager();
if(savedInstanceState==null) {
userFragment = UserNameFragment.newInstance();
fragmentManager.beginTransaction().add(R.id.profile, userFragment, "TAG").commit();
}
else {
userFragment = fragmentManager.findFragmentByTag("TAG");
}
}
How to save scroll position?
That happens by default. Read this answer for more detail.
EDIT
I believe this is your method
public createSecondFragment(int position){
ArticleReaderFrag newFragment = new ArticleReaderFrag();
Bundle args = new Bundle();
args.putString(NEW_FRAG_TITLE_KEY, item);
args.putString(NEW_FRAG_BODY_KEY, itemb);
newFragment.setArguments(args);
FragmentTransaction transaction =
getSupportFragmentManager().beginTransaction();
transaction.replace(R.id.main_activity, newFragment);
transaction.addToBackStack(null);
transaction.commit();
}
Save the position of on rotation and use that position to load the specific fragment.
Call the method when the activity is recreated after orientation change
#Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.first_activity);
if(savedInstanceState!=null) {
int lastSavedPosition = // Your logic
createSecondFragment(lastSavedPosition )
}
}

How to transfer data from different fragments in tabLayout?

I have a problem passing the selected Item of my ListView to another fragment.
I have a TabbedActivity with 2 tabs. 1st is called OngletCours and the 2nd is called OngletNotes.
I'm getting an error while passing the Item I clicked on.
I have tried the whole weekend but without sucess to transfer the Item I clicked on to the 2nd tab/fragment.
Here is the code from my 1st Fragment/Tab OngletCours (I'm only showing you the setOnItemClickListener :
l1.setOnItemClickListener(new AdapterView.OnItemClickListener()
{
#Override
public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {
OngletNotes fragment = ((Onglets)getActivity()).getOngletNotes();
if(fragment == null) {
fragment = OngletNotes.newInstance();
}
//récupération de la position convertie en String de l'item que j'ai choisi
String item = l1.getItemAtPosition(i).toString();
Bundle args = new Bundle();
args.putString("Item",item);
fragment.setArguments(args);
getFragmentManager().beginTransaction().add(R.id.container, fragment).addToBackStack(null).commit();
((Onglets)getActivity()).goToFragment(1);
}
});
My 2nd tab/Fragment OngletNotes looks like this :
public class OngletNotes extends Fragment {
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.ongletnotes, container, false);
//where i want to insert the selectedItem
TextView Cours = (TextView)rootView.findViewById(R.id.TVCours);
Bundle bundle=getArguments();
String cours="";
//ERROR !
cours = bundle.getString("Item");
//Retrieve the value
Cours.setText(cours);
return rootView;
}
public static OngletNotes newInstance() {
OngletNotes fragment = new OngletNotes();
// put values which you want to pass to fragment
// Bundle args = new Bundle();
// fragment.setArguments(args);
return fragment;
}
I have the following error :
03-06 12:48:13.959 1033-1033/com.example.dasilvadd.students E/AndroidRuntime: FATAL EXCEPTION: main
java.lang.NullPointerException
at com.example.dasilvadd.students.OngletNotes.onCreateView(OngletNotes.java:23)
Line 23 is the following one :
Bundle bundle=getArguments();
Please help me solving this, I really need to advance in my project. Thank you in advance !

Use shared preferences, create a shared preference in OngletCours then read from in OngletNotes. there is a single instance of this class that all clients share , so in this case it makes sense.Go to this link to refresh it code syntax.https://developer.android.com/training/basics/data-storage/shared-preferences.html
hey just remember this for future purposes, serialize your data whenever your store it. a great library is gson. Gson is a Java library that can be used to convert Java Objects into their JSON representation. It can also be used to convert a JSON string to an equivalent Java object. Gson can work with arbitrary Java objects including pre-existing objects that you do not have source-code of.Just something to think about still.

try this
Use Bundle to send String:
YourFragment fragment = new YourFragment();
Bundle bundle = new Bundle();
bundle.putString("YourKey", "YourValue");
fragment.setArguments(bundle);
//Inflate the fragment
getFragmentManager().beginTransaction().add(R.id.container,fragment).commit();
In onCreateView of the new Fragment:
//Retrieve the value
String value = getArguments().getString("YourKey");
i hope it will work for your case

Provide a constructor for your fragment
public OngletNotes () {
setArguments(new Bundle());
}

Don't use Bundle for transfer data if you have only two framgent in the tab.
I will explain you from the beginning..
For ViewPager you need list of Fragments right. Just like below
List<Fragment> fragmentsList = new ArrayList<Fragment>();
fragmentsList.add(Fragment1)-->OngletCours
fragmentsList.add(Fragment2)-->OngletNotes
You will pass the above list in ViewPagerAdapter.
Have one function in Fragment2 like below
public void getDataFromFragmentOne(String item){
// Do the mannipulation
}
When the item clicked in FragmentOne Just call the above function like below
((OngletNotes)getParentFragment.fragmentsList.get(1)).getDataFromFragmentOne(item)..
The above should work perfectly..Because you are not handling data in onCreateView or onCreate.. Whenever the item is clicked you will pass the data to the secondframent which is already there in viewpager because of offsreenpage limt.

in Case of kotlin you can create newInstance in fragment;
class TeamTwoFragment :Fragment {
lateinit var eventsX: EventsX
lateinit var stateList: StateList
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
}
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
arguments?.let {
eventsX = it.getParcelable (EVENT_X)!!
stateList = it.getParcelable(STATE_LIST)!!
}
}
fun newInstance(someInt: EventsX, events: StateList): TeamTwoFragment {
val myFragment = TeamTwoFragment().apply {
val args = Bundle()
args.putParcelable(EVENT_X, someInt)
args.putParcelable(STATE_LIST, events)
setArguments(args)
}
return myFragment
}
And from tablayout activity or fragments when setup tablayout:
setupViewPager(binding.viewPager,TeamOneFragment().newInstance(eventsX,events))

How can I recreate a fragment?

I'm using a widget called SwipeRefreshLayout, to refresh my fragment when someone pushes the view.
To recreate the activity I have to use:
SwipeRefreshLayout mSwipeRefreshLayout;
public static LobbyFragment newInstance() {
return new LobbyFragment();
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
final View view = inflater.inflate(R.layout.fragment_lobby, container, false);
receiver = new MySQLReceiver();
rlLoading = (RelativeLayout) view.findViewById(R.id.rlLoading);
gvLobby = (GridView) view.findViewById(R.id.gvLobby);
updateList();
mSwipeRefreshLayout = (SwipeRefreshLayout) view.findViewById(R.id.mSwipeRefreshLayout);
mSwipeRefreshLayout.setColorSchemeResources(R.color.pDarkGreen, R.color.pDarskSlowGreen, R.color.pLightGreen, R.color.pFullLightGreen);
mSwipeRefreshLayout.setOnRefreshListener(new SwipeRefreshLayout.OnRefreshListener() {
#Override
public void onRefresh() {
getActivity().recreate();
}
});
return view;
}
But I don't want to recreate the full activity that contains the view pager, I would like to recreate the fragment. How can I do that?

I'm using .detach() and .attach() for recreating the fragment.
ATTACH
Re-attach a fragment after it had previously been deatched from the UI with detach(Fragment). This causes its view hierarchy to be re-created, attached to the UI, and displayed.
DETACH
Detach the given fragment from the UI. This is the same state as when it is put on the back stack: the fragment is removed from the UI, however its state is still being actively managed by the fragment manager. When going into this state its view hierarchy is destroyed.
HOW I USE IT
getFragmentManager()
.beginTransaction()
.detach(LobbyFragment.this)
.attach(LobbyFragment.this)
.commit();

You can use :
getSupportFragmentManager().beginTransaction()
.replace(R.id.container, LobbyFragment.newInstance()).commit();
To recreate your fragment
Note:getSupportFragmentManager() is if you are using support fragment and AppCompatActivity , if you are using framework fragment class you need to use getFragmentManager()

If you're using Navigation Component, you can use this:
findNavController().navigate(
R.id.current_dest,
arguments,
NavOptions.Builder()
.setPopUpTo(R.id.current_dest, true)
.build()
)
This lets NavController pop up the current fragment and then navigate to itself. You get a new Fragment and fragment ViewModel also gets recreated.

For Kotlin Lover
if you want to recreate fragment you should dettach() fragment then attach() fragment
please follow this step
setp : 1 , first create a method recreateFragment() on your activity class
fun recreateFragment(fragment : Fragment){
if(Build.VERSION.SDK_INT >= Build.VERSION_CODES.N){
supportFragmentManager.beginTransaction().detach(fragment).commitNow()
supportFragmentManager.beginTransaction().attach(fragment).commitNow()
}else{
supportFragmentManager.beginTransaction().detach(fragment).attach(fragment).commitNow()
}
}
step : 2 , then call this method on your fragment to recreate this fragment
suppose A Button click then recreate this fragment
button.setOnClickListener {
(activity as yourActivity).recreateFragment(this)
}

If you want to refresh from activity then use:
getSupportfragmentmanager()
.begintransaction
.detach(fragment)
.attach(fragment)
.addtobackstack(null)
.commit();
and if you are in fragment already then use:
public class MyDetailFragment extends Fragment {
....
private void refreshFragment(){
getFragmentManager()
.beginTransaction()
.detach(this)
.attach(this)
.addToBackStack(null)
.commit();
}
...
}

who use Navigation Component !! :
just put a self destination .
<action
android:id="#+id/action_piecesReferenceCount_self"
app:destination="#id/piecesReferenceCount" />
Navigation.findNavController(myview).navigate(R.id.action_piecesReferenceCount_self);

Using the method from Ciardini I got errors sometimes. This works always:
FragmentTransaction ft = getFragmentManager().beginTransaction();
if (Build.VERSION.SDK_INT >= 26) {
ft.setReorderingAllowed(false);
}
ft.detach(this).attach(this).commitAllowingStateLoss();

I had to use 2 transactions for the fragment to reload its content list:
FragmentTransaction ftr = getSupportFragmentManager().beginTransaction();
ftr.detach(localCurrentPrimaryItem)
.commit();
FragmentTransaction ftr2 = getSupportFragmentManager().beginTransaction();
ftr2.attach(localCurrentPrimaryItem)
.commit();

In my case, I had a fragment that needed to be recreated when I clicked on a button, what I did was the following in the onCreateView of the fragment (MyFragmentClass) class:
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
...
Button annuler = (Button) rootView.findViewById(R.id.buttonAnnulerCreation);
annuler.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
getParentFragmentManager().beginTransaction().replace(R.id.fragmentLayout, new MyFragmentClass()).commit();
}
}); }

Define a Kotlin extension function:
/**
* Recreate a fragment without recreating any associated fragment view model. This is useful if initially some work needs
* to be done to set up the data for a fragment. At the start the layout shows a "working" fragment state. When the work completes
* the fragment view model is set to indicate the data is available, and this triggers a different layout to be inflated.
*
* This causes [Fragment.onDestroy] followed by [Fragment.onViewCreated] to be called (but not [Fragment.onCreate]).
*
* For background see [Stackoverflow](https://stackoverflow.com/questions/39296873/how-can-i-recreate-a-fragment)
*/
fun Fragment.recreateFragment() {
val fragment = this
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {
parentFragmentManager.beginTransaction().detach(fragment).commitNow()
parentFragmentManager.beginTransaction().attach(fragment).commitNow()
} else {
parentFragmentManager.beginTransaction().detach(fragment).attach(fragment).commitNow()
}
}