[android] How to save RecyclerView's scroll position using RecyclerView.State?

I have a question about Android's RecyclerView.State.

I am using a RecyclerView, how could I use and bind it with RecyclerView.State?

My purpose is to save the RecyclerView's scroll position.

I had the same problem with a minor difference, I was using Databinding, and I was setting recyclerView adapter and the layoutManager in the binding methods.

The problem was that data-binding was happening after onResume so it was resetting my layoutManager after onResume and that means it was scrolling back to original place every time. So when I stopped setting layoutManager in Databinding adaptor methods, it works fine again.

You can either use adapter.stateRestorationPolicy = StateRestorationPolicy.PREVENT_WHEN_EMPTY which is introduced in recyclerview:1.2.0-alpha02

https://medium.com/androiddevelopers/restore-recyclerview-scroll-position-a8fbdc9a9334

but it has some issues such as not working with inner RecyclerView, and some other issues you can check out in medium post's comment section.

Or you can use ViewModel with SavedStateHandle which works for inner RecyclerViews, screen rotation and process death.

Create a ViewModel with saveStateHandle

val scrollState=
    savedStateHandle.getLiveData<Parcelable?>(KEY_LAYOUT_MANAGER_STATE)

use Parcelable scrollState to save and restore state as answered in other posts or by adding a scroll listener to RecyclerView and

recyclerView.addOnScrollListener(object : RecyclerView.OnScrollListener() {

        override fun onScrollStateChanged(recyclerView: RecyclerView, newState: Int) {
            super.onScrollStateChanged(recyclerView, newState)
            if (newState == RecyclerView.SCROLL_STATE_IDLE) {
               scrollState.value = mLayoutManager.onSaveInstanceState()
            }
        }

I wanted to save Recycler View's scroll position when navigating away from my list activity and then clicking the back button to navigate back. Many of the solutions provided for this problem were either much more complicated than needed or didn't work for my configuration, so I thought I'd share my solution.

First save your instance state in onPause as many have shown. I think it's worth emphasizing here that this version of onSaveInstanceState is a method from the RecyclerView.LayoutManager class.

private LinearLayoutManager mLayoutManager;
Parcelable state;

        @Override
        public void onPause() {
            super.onPause();
            state = mLayoutManager.onSaveInstanceState();
        }

The key to getting this to work properly is to make sure you call onRestoreInstanceState after you attach your adapter, as some have indicated in other threads. However the actual method call is much simpler than many have indicated.

private void someMethod() {
    mVenueRecyclerView.setAdapter(mVenueAdapter);
    mLayoutManager.onRestoreInstanceState(state);
}

This is how I restore RecyclerView position with GridLayoutManager after rotation when you need to reload data from internet with AsyncTaskLoader.

Make a global variable of Parcelable and GridLayoutManager and a static final string:

private Parcelable savedRecyclerLayoutState;
private GridLayoutManager mGridLayoutManager;
private static final String BUNDLE_RECYCLER_LAYOUT = "recycler_layout";

Save state of gridLayoutManager in onSaveInstance()

 @Override
        protected void onSaveInstanceState(Bundle outState) {
            super.onSaveInstanceState(outState);
            outState.putParcelable(BUNDLE_RECYCLER_LAYOUT, 
            mGridLayoutManager.onSaveInstanceState());
        }

Restore in onRestoreInstanceState

@Override
    protected void onRestoreInstanceState(Bundle savedInstanceState) {
        super.onRestoreInstanceState(savedInstanceState);

        //restore recycler view at same position
        if (savedInstanceState != null) {
            savedRecyclerLayoutState = savedInstanceState.getParcelable(BUNDLE_RECYCLER_LAYOUT);
        }
    }

Then when loader fetches data from internet you restore recyclerview position in onLoadFinished()

if(savedRecyclerLayoutState!=null){
                mGridLayoutManager.onRestoreInstanceState(savedRecyclerLayoutState);
            }

..of course you have to instantiate gridLayoutManager inside onCreate. Cheers

Store

lastFirstVisiblePosition = ((LinearLayoutManager)rv.getLayoutManager()).findFirstCompletelyVisibleItemPosition();

Restore

((LinearLayoutManager) rv.getLayoutManager()).scrollToPosition(lastFirstVisiblePosition);

and if that doesn't work, try

((LinearLayoutManager) rv.getLayoutManager()).scrollToPositionWithOffset(lastFirstVisiblePosition,0)

Put store in onPause() and restore in onResume()

Update

Starting from recyclerview:1.2.0-alpha02 release StateRestorationPolicy has been introduced. It could be a better approach to the given problem.

This topic has been covered on android developers medium article.

Also, @rubén-viguera shared more details in the answer below. https://stackoverflow.com/a/61609823/892500

Old answer

If you are using LinearLayoutManager, it comes with pre-built save api linearLayoutManagerInstance.onSaveInstanceState() and restore api linearLayoutManagerInstance.onRestoreInstanceState(...)

With that, you can save the returned parcelable to your outState. e.g.,

outState.putParcelable("KeyForLayoutManagerState", linearLayoutManagerInstance.onSaveInstanceState());

, and restore restore position with the state you saved. e.g,

Parcelable state = savedInstanceState.getParcelable("KeyForLayoutManagerState");
linearLayoutManagerInstance.onRestoreInstanceState(state);

To wrap all up, your final code will look something like

private static final String BUNDLE_RECYCLER_LAYOUT = "classname.recycler.layout";

/**
 * This is a method for Fragment. 
 * You can do the same in onCreate or onRestoreInstanceState
 */
@Override
public void onViewStateRestored(@Nullable Bundle savedInstanceState) {
    super.onViewStateRestored(savedInstanceState);

    if(savedInstanceState != null)
    {
        Parcelable savedRecyclerLayoutState = savedInstanceState.getParcelable(BUNDLE_RECYCLER_LAYOUT);
        recyclerView.getLayoutManager().onRestoreInstanceState(savedRecyclerLayoutState);
    }
}

@Override
public void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);
    outState.putParcelable(BUNDLE_RECYCLER_LAYOUT, recyclerView.getLayoutManager().onSaveInstanceState());
}

Edit: You can also use the same apis with the GridLayoutManager, as it is a subclass of LinearLayoutManager. Thanks @wegsehen for the suggestion.

Edit: Remember, if you are also loading data in a background thread, you will need to a call to onRestoreInstanceState within your onPostExecute/onLoadFinished method for the position to be restored upon orientation change, e.g.

@Override
protected void onPostExecute(ArrayList<Movie> movies) {
    mLoadingIndicator.setVisibility(View.INVISIBLE);
    if (movies != null) {
        showMoviePosterDataView();
        mDataAdapter.setMovies(movies);
      mRecyclerView.getLayoutManager().onRestoreInstanceState(mSavedRecyclerLayoutState);
        } else {
            showErrorMessage();
        }
    }

All layout managers bundled in the support library already know how to save and restore scroll position.

Scroll position is restored on the first layout pass which happens when the following conditions are met:

• a layout manager is attached to the RecyclerView
• an adapter is attached to the RecyclerView

Typically you set the layout manager in XML so all you have to do now is

1. Load the adapter with data
2. Then attach the adapter to the RecyclerView

You can do this at any time, it's not constrained to Fragment.onCreateView or Activity.onCreate.

Example: Ensure the adapter is attached every time the data is updated.

viewModel.liveData.observe(this) {
    // Load adapter.
    adapter.data = it

    if (list.adapter != adapter) {
        // Only set the adapter if we didn't do it already.
        list.adapter = adapter
    }
}

The saved scroll position is calculated from the following data:

• Adapter position of the first item on the screen
• Pixel offset of the top of the item from the top of the list (for vertical layout)

Therefore you can expect a slight mismatch e.g. if your items have different dimensions in portrait and landscape orientation.

The RecyclerView/ScrollView/whatever needs to have an android:id for its state to be saved.

Activity.java:

public RecyclerView.LayoutManager mLayoutManager;

Parcelable state;

    mLayoutManager = new LinearLayoutManager(this);


// Inside `onCreate()` lifecycle method, put the below code :

    if(state != null) {
    mLayoutManager.onRestoreInstanceState(state);

    } 

    @Override
    protected void onResume() {
        super.onResume();

        if (state != null) {
            mLayoutManager.onRestoreInstanceState(state);
        }
    }   

   @Override
    protected void onPause() {
        super.onPause();

        state = mLayoutManager.onSaveInstanceState();

    }   

Why I'm using OnSaveInstanceState() in onPause() means, While switch to another activity onPause would be called.It will save that scroll position and restore the position when we coming back from another activity.

Beginning from version 1.2.0-alpha02 of androidx recyclerView library, it is now automatically managed. Just add it with:

implementation "androidx.recyclerview:recyclerview:1.2.0-alpha02"

And use:

adapter.stateRestorationPolicy = StateRestorationPolicy.PREVENT_WHEN_EMPTY

The StateRestorationPolicy enum has 3 options:

• ALLOW — the default state, that restores the RecyclerView state immediately, in the next layout pass
• PREVENT_WHEN_EMPTY — restores the RecyclerView state only when the adapter is not empty (adapter.getItemCount() > 0). If your data is loaded async, the RecyclerView waits until data is loaded and only then the state is restored. If you have default items, like headers or load progress indicators as part of your Adapter, then you should use the PREVENT option, unless the default items are added using MergeAdapter. MergeAdapter waits for all of its adapters to be ready and only then it restores the state.
• PREVENT — all state restoration is deferred until you set ALLOW or PREVENT_WHEN_EMPTY.

Note that at the time of this answer, recyclerView library is still in alpha03, but alpha phase is not suitable for production purposes.

Here is my Approach to save them and maintain the state of recyclerview in a fragment. First, add config changes in your parent activity as below code.

android:configChanges="orientation|screenSize"

Then in your Fragment declare these instance method's

private  Bundle mBundleRecyclerViewState;
private Parcelable mListState = null;
private LinearLayoutManager mLinearLayoutManager;

Add below code in your @onPause method

@Override
public void onPause() {
    super.onPause();
    //This used to store the state of recycler view
    mBundleRecyclerViewState = new Bundle();
    mListState =mTrailersRecyclerView.getLayoutManager().onSaveInstanceState();
    mBundleRecyclerViewState.putParcelable(getResources().getString(R.string.recycler_scroll_position_key), mListState);
}

Add onConfigartionChanged Method like below.

@Override
public void onConfigurationChanged(Configuration newConfig) {
    super.onConfigurationChanged(newConfig);
    //When orientation is changed then grid column count is also changed so get every time
    Log.e(TAG, "onConfigurationChanged: " );
    if (mBundleRecyclerViewState != null) {
        new Handler().postDelayed(new Runnable() {

            @Override
            public void run() {
                mListState = mBundleRecyclerViewState.getParcelable(getResources().getString(R.string.recycler_scroll_position_key));
                mTrailersRecyclerView.getLayoutManager().onRestoreInstanceState(mListState);

            }
        }, 50);
    }
    mTrailersRecyclerView.setLayoutManager(mLinearLayoutManager);
}

This approch will reslove your problem. if You have diffrent layout manager then just replace upper layout manager.

I've had the same requirement, but the solutions here didn't quite get me across the line, due to the source of data for the recyclerView.

I was extracting the RecyclerViews' LinearLayoutManager state in onPause()

private Parcelable state;

Public void onPause() {
    state = mLinearLayoutManager.onSaveInstanceState();
}

Parcelable state is saved in onSaveInstanceState(Bundle outState), and extracted again in onCreate(Bundle savedInstanceState), when savedInstanceState != null.

However, the recyclerView adapter is populated and updated by a ViewModel LiveData object returned by a DAO call to a Room database.

mViewModel.getAllDataToDisplay(mSelectedData).observe(this, new Observer<List<String>>() {
    @Override
    public void onChanged(@Nullable final List<String> displayStrings) {
        mAdapter.swapData(displayStrings);
        mLinearLayoutManager.onRestoreInstanceState(state);
    }
});

I eventually found that restoring the instance state directly after the data is set in the adapter would keep the scroll-state across rotations.

I suspect this either is because the LinearLayoutManager state that I'd restored was being overwritten when the data was returned by the database call, or the restored state was meaningless against an 'empty' LinearLayoutManager.

If the adapter data is available directly (ie not contigent on a database call), then restoring the instance state on the LinearLayoutManager can be done after the adapter is set on the recyclerView.

The distinction between the two scenarios held me up for ages.

I Set variables in onCreate(), save scroll position in onPause() and set scroll position in onResume()

public static int index = -1;
public static int top = -1;
LinearLayoutManager mLayoutManager;

@Override
public void onCreate(Bundle savedInstanceState)
{
    //Set Variables
    super.onCreate(savedInstanceState);
    cRecyclerView = ( RecyclerView )findViewById(R.id.conv_recycler);
    mLayoutManager = new LinearLayoutManager(this);
    cRecyclerView.setHasFixedSize(true);
    cRecyclerView.setLayoutManager(mLayoutManager);

}

@Override
public void onPause()
{
    super.onPause();
    //read current recyclerview position
    index = mLayoutManager.findFirstVisibleItemPosition();
    View v = cRecyclerView.getChildAt(0);
    top = (v == null) ? 0 : (v.getTop() - cRecyclerView.getPaddingTop());
}

@Override
public void onResume()
{
    super.onResume();
    //set recyclerview position
    if(index != -1)
    {
        mLayoutManager.scrollToPositionWithOffset( index, top);
    }
}

I would just like to share the recent predicament I encounter with the RecyclerView. I hope that anyone experiencing the same problem will benefit.

My Project Requirement: So I have a RecyclerView that list some clickable items in my Main Activity (Activity-A). When the Item is clicked a new Activity is shown with the Item Details (Activity-B).

I implemented in the Manifest file the that the Activity-A is the parent of Activity-B, that way, I have a back or home button on the ActionBar of the Activity-B

Problem: Every time I pressed the Back or Home button in the Activity-B ActionBar, the Activity-A goes into the full Activity Life Cycle starting from onCreate()

Even though I implemented an onSaveInstanceState() saving the List of the RecyclerView's Adapter, when Activity-A starts it's lifecycle, the saveInstanceState is always null in the onCreate() method.

Further digging in the internet, I came across the same problem but the person noticed that the Back or Home button below the Anroid device (Default Back/Home button), the Activity-A does not goes into the Activity Life-Cycle.

Solution:

1. I removed the Tag for Parent Activity in the manifest for Activity-B

2. I enabled the home or back button on Activity-B

   Under onCreate() method add this line supportActionBar?.setDisplayHomeAsUpEnabled(true)

3. In the overide fun onOptionsItemSelected() method, I checked for the item.ItemId on which item is clicked based on the id. The Id for the back button is

   android.R.id.home

   Then implement a finish() function call inside the android.R.id.home

   This will end the Activity-B and bring Acitivy-A without going through the entire life-cycle.

For my requirement this is the best solution so far.

     override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_show_project)

    supportActionBar?.title = projectName
    supportActionBar?.setDisplayHomeAsUpEnabled(true)

}


 override fun onOptionsItemSelected(item: MenuItem?): Boolean {

    when(item?.itemId){

        android.R.id.home -> {
            finish()
        }
    }

    return super.onOptionsItemSelected(item)
}

On Android API Level 28, I simply ensure that I set up my LinearLayoutManager and RecyclerView.Adapter in my Fragment#onCreateView method, and everything Just Worked™?. I didn't need to do any onSaveInstanceState or onRestoreInstanceState work.

Eugen Pechanec's answer explains why this works.

You don't have to save and restore the state by yourself anymore. If you set unique ID in xml and recyclerView.setSaveEnabled(true) (true by default) system will automatically do it. Here is more about this: http://trickyandroid.com/saving-android-view-state-correctly/

For me, the problem was that I set up a new layoutmanager every time I changed my adapter, loosing que scroll position on recyclerView.

In my case I was setting the RecyclerView's layoutManager both in XML and in onViewCreated. Removing the assignment in onViewCreated fixed it.

with(_binding.list) {
//  layoutManager =  LinearLayoutManager(context)
    adapter = MyAdapter().apply {
        listViewModel.data.observe(viewLifecycleOwner,
            Observer {
                it?.let { setItems(it) }
            })
    }
}