RecyclerView存储/还原活动之间的状态

Question 1

我正在将ListViews迁移到RecyclerViews。对于列表视图，我使用了此处介绍的通用技术来存储和恢复活动之间的滚动位置。

如何使用RecyclerViews进行相同操作？在RecyclerView.onSaveInstanceState()似乎有protected访问权限，因此无法直接使用。

Question 2

好吧，所以回答我自己的问题。据我了解，由于它们已将布局代码和视图回收代码（因此称为名称）分离，因此负责保持布局状态（并还原其状态）的组件现在已LayoutManager在您的recyclerview中使用。

因此，要存储状态，请使用相同的模式，但要在布局管理器而不是recyclerview上：

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

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

恢复状态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);
}

然后更新LayoutManager（我在中做onResume()）：

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

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

Question 3

我找到了一个更好的解决方案-该解决方案具有以下优点：

RecyclerView状态会在手机旋转时保存和恢复
RecyclerView状态在通过RecyclerView返回活动时得以保存和恢复（在显示其他活动时未销毁该状态-这意味着onRestoreInstanceState()不称为!!）

码

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);
        }
    }
}

Question 4

在onPause()和中使用此代码onResume()可保存和恢复滚动位置-

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

Question 5

那是我的解决方案，它可以还原项目和RecyclerView的位置

1）在onSaveInstanceState方法中保存回收者视图状态

@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）在onCreate方法中检查savedInstanceState Bundle

@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）如果屏幕已旋转，则还原回收者视图数据

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);
}

Question 6

您可以使用adapter.stateRestorationPolicy = StateRestorationPolicy.PREVENT_WHEN_EMPTY引入的recyclerview:1.2.0-alpha02

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

但是它存在一些问题，例如不能与内部RecyclerView一起使用，以及一些其他问题，您可以在中篇文章的评论部分中查看。

或者你可以使用ViewModel与SavedStateHandle该作品内RecyclerViews，屏幕旋转和工艺死亡。

创建一个ViewModel与saveStateHandle

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

使用包裹 scrollState来保存和恢复状态，如在其他帖子中回答的那样，或者通过向RecyclerView添加滚动侦听器并

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

    override fun onScrollStateChanged(recyclerView: RecyclerView, newState: Int) {
        super.onScrollStateChanged(recyclerView, newState)
        if (newState == RecyclerView.SCROLL_STATE_IDLE) {
           // save here
        }
    }

Question 7

使用时，recyclerView.getLayoutManager().onSaveInstanceState()请不要忘记检查null：

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

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

Question 8

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
    }
}

Question 9

考虑到您已经在代码中定义了RecyclerView（mRecyclerView）和LayoutManager（mLayoutManager），并且到目前为止一切工作正常，因此保存mPositionRecyclerView的position（）的解决方案如下所示：

使用的变量和常量：

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

在onPause方法中：

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

    // Save RecyclerView state
    mBundleState = new Bundle();
    mPosition = mLayoutManager.findFirstCompletelyVisibleItemPosition();
    mBundleState.putInt(RECYCLER_POSITION_KEY, mPosition);
}

在onResume方法中：

@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);
    }
}

在onSaveInstanceState方法中：

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

    super.onSaveInstanceState(outState);
}

在onRestoreInstanceState方法中：

@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);
}