如何使用RecyclerView.State保存RecyclerView滚动位置？

我有一个关于 Android 的问题RecyclerView.State http://developer.android.com/reference/android/support/v7/widget/RecyclerView.State.html.

我正在使用 RecyclerView，如何使用它并将其与 RecyclerView.State 绑定？

我的目的是保存RecyclerView的滚动位置.

Update

从...开始recyclerview:1.2.0-alpha02发布StateRestorationPolicy已被介绍。这可能是解决给定问题的更好方法。

该主题已被涵盖Android 开发者媒体文章 https://medium.com/androiddevelopers/restore-recyclerview-scroll-position-a8fbdc9a9334.

此外，@rubén-viguera 在下面的答案中分享了更多详细信息。https://stackoverflow.com/a/61609823/892500 https://stackoverflow.com/a/61609823/892500

旧答案

如果您使用 LinearLayoutManager，它带有预构建的保存 apiLinearLayoutManager Instance.onSaveInstanceState() http://grepcode.com/file/repository.grepcode.com/java/ext/com.google.android/android/5.0.0_r1/android/support/v7/widget/LinearLayoutManager.java#LinearLayoutManager.onSaveInstanceState%28%29并恢复apiLinearLayoutManager Instance.onRestoreInstanceState(...) http://grepcode.com/file/repository.grepcode.com/java/ext/com.google.android/android/5.0.0_r1/android/support/v7/widget/LinearLayoutManager.java#LinearLayoutManager.onRestoreInstanceState%28android.os.Parcelable%29

这样，您就可以将返回的 Parcelable 保存到您的 outState 中。例如。，

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

，并按照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，您的最终代码将类似于

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:您还可以对 GridLayoutManager 使用相同的 api，因为它是 LinearLayoutManager 的子类。感谢@wegsehen 的建议。

Edit:请记住，如果您还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();
        }
    }