App被推到后台重新创建时，RecyclerView不恢复LayoutManager状态

Question

我最初关注the accepted answer in this previously posted question，了解如何保存和恢复 RecyclerView 的布局管理器。

我的 RecyclerView 在 Activity B 中。[注意：Activity A 将启动 Activity B，通过 Intent 传输数据。]

当用户在 Activity B 中单击视图时，会启动 Activity C。一旦 Activity C 关闭并销毁，Activity B 就可见了，我可以看到我在 RecyclerView 中恢复的所有数据。

问题： 但是，如果我离开我的应用程序（即按下 Home 键），它会被推到后台。当我的应用程序恢复时，再次调用 onCreate()。 LayoutManager 的状态正在保存，但是我的数据都没有显示在 RecyclerView 中。

我可以说我的 LayoutManager 状态在经过一些调试后被保存了。从后台恢复应用后再次调用 onCreate() 时显示如下：

Saved Instance State = Bundle[{ActivityB - Linear Layout State=android.support.v7.widget.LinearLayoutManager$SavedState@6358f8f, android:viewHierarchyState=Bundle[mParcelledData.dataSize=1296]}]

经过数小时的尝试，我不确定如何解决此问题。

我的代码：

public class ActivityB extends AppCompatActivity {

      private RecyclerView recyclerView;
      private LinearLayoutManager linearLayoutManager;
      private Parcelable linearLayoutState;
      private RecyclerAdapter adapter;
      private Button more;
      private String id;
      private List<VideoItem> list;
      private List<VideoItem> newList;
      private final String LINEARLAYOUT_STATE_KEY = "Activity B - Linear Layout State";

      @Override
      protected void onCreate(Bundle savedInstanceState) {
             super.onCreate(savedInstanceState);
             setContentView(R.layout.activity_blayout);

             // Retrieving data from Activity A
             Intent intent = getIntent();
             Bundle bundle = intent.getBundleExtra("bundle");
             someClass.innerClass class = bundle.getParcelable("data");
             id = class.getID();
             list = class.getList();
             newList = new ArrayList<>();

             // Instantiating Recycler View
             recyclerView = (RecyclerView)findViewById(R.id.activityb_recyclerview);
             recyclerView.setNestedScrollingEnabled(false);

             linearLayoutManager = new LinearLayoutManager(context);
             recyclerView.setLayoutManager(linearLayoutManager);

             adapter = new RecyclerAdapter();
             recyclerView.setAdapter(adapter);

             moreButton = (Button)findViewById(R.id.activityb_more);
             moreButton.setOnClickListener(new fetchMoreClickListener());
        }

        @Override
        public void onResume(){
              if (linearLayoutState != null) {
                 linearLayoutManager.onRestoreInstanceState(linearLayoutState);
              } else {
                 // If no layout state is found, I need to populate my
                 // adapter.
                 // Here I am simply cloning my list again, to keep the original
                 // list intact. generateSubset() removes items from the cloned list 
                 // to create a smaller subset that is added to the adapter.
                 for (ListItem item : list){
                        newList.add(new ListItemi(item));
                 }
                 adapter.addItems(generateSubset(0));
              }
              super.onResume();
        }

        @Override
        protected void onSaveInstanceState(Bundle outState) {
               linearLayoutState = linearLayoutManager.onSaveInstanceState();
               outState.putParcelable(LINEARLAYOUT_STATE_KEY, linearLayoutState);
               super.onSaveInstanceState(outState);
        }

        @Override
        protected void onRestoreInstanceState(Bundle savedInstanceState) {
               super.onRestoreInstanceState(savedInstanceState);
               linearLayoutState = savedInstanceState.getParcelable(LINEARLAYOUT_STATE_KEY);
        }

其他活动生命周期方法尚未被覆盖。我没有收到任何错误消息。只有我存储在我的视图中的数据不再显示在 RecyclerView 中。

编辑 1：

这是我的 RecyclerAdapter 代码：

公共类 RecyclerAdapter 扩展 RecyclerView.Adapter{ 现在私有静态日期； 私有列表列表；

public static class ItemHolder extends RecyclerView.ViewHolder
        implements View.OnClickListener {

    private Context context;
    private String key;
    private Bundle itemBundle;
    private SimpleDraweeView photo;
    private TextView title;

    public ItemHolder(Context context, View view){
        super(view);

        this.context = context;
        this.key = null;
        this.itemBundle = null;
        photo = (SimpleDraweeView)view.findViewById(R.id.itemholder_photo);
        title = (TextView)view.findViewById(R.id.itemholder_title);
        view.setOnClickListener(this);
    }

    public void bindData(Item item){
        if (key == null){ key = item.getID(); }
        if (itemBundle == null){
            itemBundle = new Bundle();
            itemBundle.setClassLoader(Item.class.getClassLoader());
            itemBundle.putParcelable("data", item);
        }

        photo.setImageURI(Uri.parse(item.getPhotoURL()));
    }

    @Override
    public void onClick(View view) {
        Intent intent = new Intent(context, ActivityB.class);
        intent.putExtra("bundle", itemBundle);
        context.startActivity(intent);
    }
}

public RecyclerAdapter(){
    this.list = new ArrayList<>();
    this.now = new Date();
}

public RecyclerAdapter(ArrayList<VideoItem> list){
    this.list = list;
    this.now = new Date();
    this.notifyItemRangeInserted(0, list.size());
}

@Override
public RecyclerAdapter.ItemHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    Context context = parent.getContext();
    View recyclerItem = LayoutInflater.from(context)
            .inflate(R.layout.itemholder_item, parent, false);

    return new ItemHolder(context, recyclerItem);
}

@Override
public void onBindViewHolder(RecyclerAdapter.ItemHolder holder, int position) {
    Item item = list.get(position);
    holder.bindData(item);
}

private static Date getNow(){ return now; }

private static void updateNow(){ now = new Date(); }

@Override
public int getItemCount() {
    return list.size();
}

public void addItem(Item item){
    list.add(item);
    this.notifyItemInserted(list.size() - 1);
}

public void addItems(ArrayList<Item> items){
    int oldSize = list.size();
    list.addAll(items);
    this.notifyItemRangeInserted(oldSize, items.size());
}

}

Answer 1

尝试将您的 onResume() 方法更改为如下所示：

@Override
    public void onResume(){
          super.onResume(); 
          if (linearLayoutState != null) {
             linearLayoutManager.onRestoreInstanceState(linearLayoutState);
          } 
             // Here comes the code to populate your data. 
             // I'm not sure how you do this, so I just copy/paste your code
             for (ListItem item : list){
                    newList.add(new ListItemi(item));
             }
             // Now instatiate and add the adapter to the RecyclerView
             adapter = new RecyclerAdapter(newList);
             recyclerView.setAdapter(adapter);
          }
    }