Question

我将ListViews迁移到RecyclerViews。使用listviews，我使用了here描述的常用技术来存储和恢复活动之间的滚动位置。

如何使用RecyclerViews做同样的事情？ RecyclerView.onSaveInstanceState()似乎有protected访问权限，因此无法直接使用。

Answer 1

好的，那么回答我自己的问题。据我所知，由于它们已经将布局代码和视图回收代码（因此名称）分离，因此负责保持布局状态（并恢复它）的组件现在是您的recyclerview中使用的LayoutManager。

因此，要存储您使用相同模式的状态，但是在布局管理器而不是Recyclerview：

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

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

onRestoreInstanceState()中的恢复状态：

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onResume()中执行）：

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

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

Answer 2

我找到了更好的解决方案 - 此解决方案具有以下优势：

在旋转电话
使用RecyclerView保存并恢复返回活动的RecyclerView状态（在其他活动显示时未被销毁 - 这意味着onRestoreInstanceState()不是{\ n}叫!!）

<强> 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);
        }
    }
}

Answer 3

在onPause()和onResume()中使用此代码来保存和恢复滚动位置 -

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

Answer 4

这是我的解决方案，它会恢复两个项目和RecyclerView位置

1）在onSaveInstanceState方法中保存Recycler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，则恢复回收者视图数据

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);
}

Answer 5

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

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

但是它有一些问题，例如不能与内部RecyclerView一起使用，还有一些其他问题，您可以在中篇文章的评论部分中查看。

或者您可以将ViewModel与SavedStateHandle一起使用，这适用于内部RecyclerViews，屏幕旋转和进程死亡。

使用ViewModel创建一个saveStateHandle

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

使用Parcelable scrollState来保存和恢复状态，如在其他帖子中所回答的那样，或者通过向RecyclerView添加滚动侦听器和

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

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

Answer 6

当您使用recyclerView.getLayoutManager().onSaveInstanceState()时，请勿忘记检查 null ：

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

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

Answer 7

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
    }
}

Answer 8

我知道我迟到了，但如果它有帮助的话！

存储回收站视图位置比其他答案看起来要简单得多

你可以这样做

先创建一个成员变量

Parcelable state;

现在

@Override
protected void onPause() {
    super.onPause();
    state = recyclerView.getLayoutManager().onSaveInstanceState();
}

@Override
protected void onResume() {
    super.onResume();
    recyclerView.getLayoutManager().onRestoreInstanceState(state);
}

使用上面的代码覆盖暂停和恢复方法，你就可以开始了！！

Answer 9

考虑到您在代码中定义了RecyclerView（mRecyclerView）和LayoutManager（mLayoutManager）并且到目前为止一切正常，保存位置的解决方案（mPosition）您的RecyclerView看起来像这样：

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);
}

RecyclerView存储/恢复活动之间的状态

9 个答案: