Question

我正在尝试创建一个简单的DiffUtil适配器以与RecyclerView一起使用，但没有任何显示（我只得到一个空白活动）。这是代码：

MainActivity.java：

public class MainActivity extends AppCompatActivity {

    private MyAdapter mAdapter;
    private ArrayList<User> myDataset;
    private RecyclerView mRecyclerView;

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

        mAdapter = new MyAdapter();
        myDataset = new ArrayList<User>();

        mRecyclerView = (RecyclerView) findViewById(R.id.my_recycler_view);


        myDataset.add(new User("User1"));
        myDataset.add(new User("User2"));
        myDataset.add(new User("User3"));

        mRecyclerView.setAdapter(mAdapter);

        mAdapter.updateList(myDataset);
    }
}

这里是MyAdapter.java：

public class MyAdapter extends RecyclerView.Adapter<MyAdapter.MyViewHolder> {

    private AsyncListDiffer<User> mAsyncListDiffer;

    public static class MyViewHolder extends RecyclerView.ViewHolder {

        public TextView singleItemTextView;
        public View layout;
        public ConstraintLayout constraintLayout;

        public MyViewHolder(View v) {
            super(v);
            layout = v;
            singleItemTextView = (TextView) v.findViewById(R.id.singleItemTextView);
            constraintLayout = (ConstraintLayout) v.findViewById(R.id.constraintLayout);
        }
    }

    // Provide a suitable constructor (depends on the kind of dataset)
    public MyAdapter() {
        DiffUtil.ItemCallback<User> diffUtilCallback = new DiffUtil.ItemCallback<User>() {

            @Override
            public boolean areItemsTheSame(@NonNull User newUser, @NonNull User oldUser) {
                return newUser.getUserId().equals(oldUser.getUserId());
            }

            @Override
            public boolean areContentsTheSame(@NonNull User newUser, @NonNull User oldUser) {
                return newUser.equals(oldUser);
            }
        };
        mAsyncListDiffer = new AsyncListDiffer<>(this, diffUtilCallback);
    }

    // Create new views (invoked by the layout manager)
    @Override
    public MyAdapter.MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View v = LayoutInflater.from(parent.getContext()).inflate(R.layout.single_text_view, parent, false);
        MyViewHolder vh = new MyViewHolder(v);
        return vh;
    }

    @Override
    public void onBindViewHolder(final MyViewHolder holder, final int position) {
        User user = mAsyncListDiffer.getCurrentList().get(position);
        holder.singleItemTextView.setText(user.getUserId());
    }

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

    public void updateList(ArrayList<User> newList) {
        mAsyncListDiffer.submitList(newList);
    }

}

这里是User.java：

public class User {

    private String mUserId;

    public User(String userId) {
        mUserId = userId;
    }

    public String getUserId() {
        return mUserId;
    }

}

以下是XML文件：

acivity_main.xml：

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">


    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/my_recycler_view"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:layout_margin="4dp"
        android:layout_marginStart="8dp"
        android:layout_marginLeft="8dp"
        android:layout_marginTop="8dp"
        android:layout_marginEnd="8dp"
        android:layout_marginRight="8dp"
        android:layout_marginBottom="8dp"
        android:background="#FFFFFF"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>

这是single_text_view.xml：

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/constraintLayout"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    tools:layout_editor_absoluteY="81dp">


    <TextView
        android:id="@+id/singleItemTextView"
        android:layout_width="78dp"
        android:layout_height="78dp"
        android:layout_marginStart="8dp"
        android:layout_marginLeft="8dp"
        android:layout_marginTop="8dp"
        android:layout_marginEnd="8dp"
        android:layout_marginRight="8dp"
        android:layout_marginBottom="8dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>

我知道DiffUtil应该比较两个不同的列表，这里我只设置了初始列表，但是仍然不应该至少显示第一个列表（在这种情况下为3个用户）？

Answer 1

您是否检查自己的getItemCount()方法是否返回大于0的值？

如果是，则应查看项目视图。首先尝试删除此视图上的约束，以查看屏幕上是否出现任何内容。

Answer 2

使用Recyclerview设置LayoutManager

    // add data on list
     private ArrayList<User> myDataset=new ArrayList;
     myDataset.add(new User("abc"));

    mRecyclerView = (RecyclerView) findViewById(R.id.my_recycler_view);
    LayoutManager layoutManager=new LinearLayoutManager(getActivity());
    mRecyclerView.setLayoutManager(layoutManager);
    mRecyclerView.setItemAnimator(new DefaultItemAnimator());
    MyAdapter myAdapter=new MyAdapter();
    mAdapter.updateList(myDataset);
    mRecyclerView.setAdapter(mAdapter);

为什么带有RecyclerView的DiffUtil无法正常工作？

2 个答案: