如何保存回收站的滚动位置使用回收站视图。州？

Question

我有一个关于Android的RecyclerView的问题。状态

我正在使用RecyclerView，如何使用它并将其与RecyclerView绑定。状态

我的目的是保存RecyclerView的滚动位置。

Answer 1

匿名用户

您计划如何使用RecyclerView保存上次保存的职位。州？

你可以一直依靠良好的保存状态。扩展回收视图，覆盖onSaveInstanceState（）和onRestoreInstanceState（）：

    @Override
    protected Parcelable onSaveInstanceState() {
        Parcelable superState = super.onSaveInstanceState();
        LayoutManager layoutManager = getLayoutManager();
        if(layoutManager != null && layoutManager instanceof LinearLayoutManager){
            mScrollPosition = ((LinearLayoutManager) layoutManager).findFirstVisibleItemPosition();
        }
        SavedState newState = new SavedState(superState);
        newState.mScrollPosition = mScrollPosition;
        return newState;
    }

    @Override
    protected void onRestoreInstanceState(Parcelable state) {
        super.onRestoreInstanceState(state);
        if(state != null && state instanceof SavedState){
            mScrollPosition = ((SavedState) state).mScrollPosition;
            LayoutManager layoutManager = getLayoutManager();
            if(layoutManager != null){
              int count = layoutManager.getItemCount();
              if(mScrollPosition != RecyclerView.NO_POSITION && mScrollPosition < count){
                  layoutManager.scrollToPosition(mScrollPosition);
              }
            }
        }
    }

    static class SavedState extends android.view.View.BaseSavedState {
        public int mScrollPosition;
        SavedState(Parcel in) {
            super(in);
            mScrollPosition = in.readInt();
        }
        SavedState(Parcelable superState) {
            super(superState);
        }

        @Override
        public void writeToParcel(Parcel dest, int flags) {
            super.writeToParcel(dest, flags);
            dest.writeInt(mScrollPosition);
        }
        public static final Parcelable.Creator<SavedState> CREATOR
                = new Parcelable.Creator<SavedState>() {
            @Override
            public SavedState createFromParcel(Parcel in) {
                return new SavedState(in);
            }

            @Override
            public SavedState[] newArray(int size) {
                return new SavedState[size];
            }
        };
    }

Answer 2

店内

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

恢复

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

如果这不管用，试试看

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

将存储放入onPause（）并在onResume（）中还原

Answer 3

从recyclerview:1.2.0-alpha02releaseStateRestorationPolicy开始引入。这可能是解决给定问题的更好方法。

android开发者的媒体文章已经介绍了这个话题。

此外，@rubén-viguera在下面的回答中分享了更多细节。https://stackoverflow.com/a/61609823/892500

如果您正在使用LinearLayoutManager，它附带了预构建的保存api linearLayoutManagerInstance.onSaveInstanceState（）和恢复api linearLayoutManagerInstance.onRestoreInstanceState（...）

这样，你就可以把退回的包裹保存到你的外站。例如。，

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

，并使用保存的状态恢复恢复位置。例如，

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

总而言之，您的最终代码如下所示

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());
}

编辑：您也可以在GridLayoutManager中使用相同的apis，因为它是LinearLayoutManager的子类。谢谢@wegsehen的建议。

编辑：请记住，如果您也在后台线程中加载数据，则需要在onPostExecute/onLoadFinished方法中调用onRestoreInstanceState，以便在方向更改时恢复位置，例如：。

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