RecyclerView存储/恢复活动之间的状态

我正在将ListViews迁移到RecyclerViews.使用listviews,我使用此处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？在RecyclerView.onSaveInstanceState()似乎有protected访问权限,因此无法直接使用.

1> khusrav..：

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好的,那么回答我自己的问题.据我所知,由于他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LayoutManager在您的recyclerview中使用.

因此,要存储状态,您使用相同的模式,但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);
}

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(我做onResume()):

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

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

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但适配器怎么样？

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您可以通过消除空检查来进一步简化onRestoreInstanceState().根据Android文档:"只有存在要恢复的已保存状态时,系统才会调用onRestoreInstanceState(),因此您无需检查Bundle是否为null".这不是我的挑剔或任何东西.

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如果从未调用`onRestoreInstanceState()`该怎么办？

2> Someone Some..：

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我找到了更好的解决方案 - 该解决方案具有以下优势:

在手机旋转时保存并恢复RecyclerView状态

使用RecyclerView 返回活动时保存并恢复RecyclerView状态(在其他活动显示时未被销毁 - 这意味着onRestoreInstanceState()未调用!!)

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);
        }
    }
}

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为什么要在`onPause()`中保存状态？此时活动不会被破坏.国家完好无损.没有什么可以恢复的.

3> 小智..：

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使用此代码onPause()并onResume()保存和恢复滚动位置 -

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

4> Nicola Galla..：

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这是我的解决方案,它恢复了物品和RecyclerView的位置

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,则恢复回收站视图数据

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);
}

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您不应使用savedInstanceState保存数据集.https://developer.android.com/topic/libraries/architecture/viewmodel.html#viewmodel_vs_savedinstancestate