How can I maintain fragment state when added to the back stack?

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();                                
        }
};

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); 

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
}

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
}