RecyclerView store / restore state between activities

问题

I'm migrating my ListViews to RecyclerViews. With listviews I used the common technique described here to store and restore scroll position between activities.

How to do the same with RecyclerViews? the RecyclerView.onSaveInstanceState() seem to have protected access, so can't be used directly.

回答1:

Ok, so to answer my own question. As I understand it, since they've decoupled the layout code and the view recycling code (thus the name), the component responsible one for holding layout state (and restoring it) is now the LayoutManager used in your recyclerview.

Thus, to store state you use same pattern, but on the layout manager and not the recyclerview:

protected void onSaveInstanceState(Bundle state) {
     super.onSaveInstanceState(state);

     // Save list state
     mListState = mLayoutManager.onSaveInstanceState();
     state.putParcelable(LIST_STATE_KEY, mListState);
}

Restore state in the onRestoreInstanceState():

protected void onRestoreInstanceState(Bundle state) {
    super.onRestoreInstanceState(state);

    // Retrieve list state and list/item positions
    if(state != null)
        mListState = state.getParcelable(LIST_STATE_KEY);
}

Then update the LayoutManager (I do in onResume()):

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

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

回答2:

I found a better solution - this solution has the following benefits :

1. RecyclerView state is saved and restored on rotation of phone
2. RecyclerView state is saved and restored on returning to activity with RecyclerView (which wasn't destroyed whilst the other activity was showing - which means that onRestoreInstanceState() isn't called !!)

CODE

public class ActivityItemList extends AppCompatActivity
{
    private final String KEY_RECYCLER_STATE = "recycler_state";
    private RecyclerView mRecyclerView;
    private static Bundle mBundleRecyclerViewState;

    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_list);//set to whatever layout name you have

        mRecyclerView = (RecyclerView) findViewById(R.id.recycler_view);//set to whatever view id you use
        // don't forget to set your adapter
    }

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

        // save RecyclerView state
        mBundleRecyclerViewState = new Bundle();
        Parcelable listState = mRecyclerView.getLayoutManager().onSaveInstanceState();
        mBundleRecyclerViewState.putParcelable(KEY_RECYCLER_STATE, listState);
    }

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

        // restore RecyclerView state
        if (mBundleRecyclerViewState != null) {
            Parcelable listState = mBundleRecyclerViewState.getParcelable(KEY_RECYCLER_STATE);
            mRecyclerView.getLayoutManager().onRestoreInstanceState(listState);
        }
    }
}

回答3:

Use this code in onPause() and onResume() to save and restore scroll position-

private Parcelable recyclerViewState;
recyclerViewState = mrecyclerView.getLayoutManager().onSaveInstanceState();//save
mrecyclerView.getLayoutManager().onRestoreInstanceState(recyclerViewState);//restore

回答4:

That's my solution, it restores both items and RecyclerView position

1) save recycler view state in onSaveInstanceState method

@Override
protected void onSaveInstanceState(Bundle outState) {
    Parcelable listState = myRecyclerView.getLayoutManager().onSaveInstanceState();
    // putting recyclerview position
    outState.putParcelable(SAVED_RECYCLER_VIEW_STATUS_ID, listState);
    // putting recyclerview items
    outState.putParcelableArrayList(SAVED_RECYCLER_VIEW_DATASET_ID,mDataset);
    super.onSaveInstanceState(outState);
}

2) Check savedInstanceState Bundle in onCreate method

@Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        if (savedInstanceState==null){
            getRemoteData(); // No saved data, get data from remote
        }else{
            restorePreviousState(); // Restore data found in the Bundle
        }
    }

3) Restore recycler view data if the screen has been rotated

public void restorePreviousState(){
    // getting recyclerview position
    mListState = mSavedInstanceState.getParcelable(SAVED_RECYCLER_VIEW_STATUS_ID);
    // getting recyclerview items
    mDataset = mSavedInstanceState.getParcelableArrayList(SAVED_RECYCLER_VIEW_DATASET_ID);
    // Restoring adapter items
    mAdapter.setItems(mDataset);
    // Restoring recycler view position
    mRvMedia.getLayoutManager().onRestoreInstanceState(mListState);
}

回答5:

When you use recyclerView.getLayoutManager().onSaveInstanceState() don't forget to check for null:

@Override
public void onSaveInstanceState(@NonNull Bundle outState) {
    super.onSaveInstanceState(outState);

    if (recyclerView != null) {
        outState.putParcelable(SCROLL_POSITION, recyclerView.getLayoutManager().onSaveInstanceState());
    }
}

回答6:

public class MainActivity extends AppCompatActivity {
Parcelable recyclerViewState;
.......
@Override
    protected void onPause() {
        super.onPause();
        recyclerViewState = MainAnecdotesView.getLayoutManager().onSaveInstanceState();//save
    }
    @Override
    protected void onResume()
    {
        super.onResume();
        if(recyclerViewState!=null)
            MainAnecdotesView.getLayoutManager().onRestoreInstanceState(recyclerViewState);//restore
    }
}

回答7:

Considering that you defined a RecyclerView (mRecyclerView) and a LayoutManager (mLayoutManager) in your code and all is working fine so far, the solution on saving the position (mPosition) of your RecyclerView looks like this:

1. Variables and constants used:

   private final String RECYCLER_POSITION_KEY = "recycler_position";
   private int mPosition = RecyclerView.NO_POSITION;
   private RecyclerView mRecyclerView;
   private LinearLayoutManager mLayoutManager;
   private static Bundle mBundleState;
   

2. In onPause method:

   @Override
   protected void onPause()
   {
       super.onPause();
   
       // Save RecyclerView state
       mBundleState = new Bundle();
       mPosition = mLayoutManager.findFirstCompletelyVisibleItemPosition();
       mBundleState.putInt(RECYCLER_POSITION_KEY, mPosition);
   }
   

3. In onResume method:

   @Override
   protected void onResume()
   {
       super.onResume();
   
       // Restore RecyclerView state
       if (mBundleState != null) {
           mPosition = mBundleState.getInt(RECYCLER_POSITION_KEY);
           if (mPosition == RecyclerView.NO_POSITION) mPosition = 0;
           // Scroll the RecyclerView to mPosition
           mRecyclerView.smoothScrollToPosition(mPosition);
       }
   }
   

4. In onSaveInstanceState method:

   @Override
   public void onSaveInstanceState(Bundle outState) {
       // Save RecyclerView state
       outState.putInt(RECYCLER_POSITION_KEY,  mLayoutManager.findFirstCompletelyVisibleItemPosition());
   
       super.onSaveInstanceState(outState);
   }
   

5. In onRestoreInstanceState method:

   @Override
   protected void onRestoreInstanceState(Bundle savedInstanceState) {
       // Restore RecyclerView state
       if (savedInstanceState.containsKey(RECYCLER_POSITION_KEY)) {
           mPosition = savedInstanceState.getInt(RECYCLER_POSITION_KEY);
           if (mPosition == RecyclerView.NO_POSITION) mPosition = 0;
           // Scroll the RecyclerView to mPosition
           mRecyclerView.smoothScrollToPosition(mPosition);
       }
   
       super.onRestoreInstanceState(savedInstanceState);
   }
   

来源：https://stackoverflow.com/questions/28236390/recyclerview-store-restore-state-between-activities