Android recyclerview 不显示任何数据

Question

我正在使用模板，并将占位符数据替换为 Retrofit 2 请求，该请求解析来自 URL 的数据的 JSON 文件并将其放入对象列表中。 我遇到了一个问题，我的改造调用首先被执行并返回 items = 0，然后代码使用值items=0进一步执行，在调试器中经过相当多的步骤后，它返回调用并显示正确响应（items=12），但 Adapter/RecycleView 操作似乎已经执行，并且它们不使用迟到的解析数据。

MainActivity.java

public class MainActivity extends AppCompatActivity {
private View parent_view;
List<Task> items = new List<Task>() {...}
private RecyclerView recyclerView;
private AdapterTasks mAdapter;
private int animation_type = ItemAnimation.BOTTOM_UP;


@Override
protected void onCreate(Bundle savedInstanceState) {
    items = DataGenerator.getTasksData();
    items.addAll(DataGenerator.getTasksData());
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_list_animation);
    parent_view = findViewById(android.R.id.content);
    initComponent();

}
private void initComponent() {

    recyclerView = (RecyclerView) findViewById(R.id.recyclerView);
    recyclerView.setLayoutManager(new LinearLayoutManager(this));
    recyclerView.setHasFixedSize(true);
    animation_type = ItemAnimation.FADE_IN;
    setAdapter();
}

private void setAdapter() {
    //set data and list adapter
    mAdapter = new AdapterTasks(this, items, animation_type);
    recyclerView.setAdapter(mAdapter);

    // on item list clicked
    mAdapter.setOnItemClickListener(new AdapterTasks.OnItemClickListener() {
        @Override
        public void onItemClick(View view, Task obj, int position) {
            //open task view
        }
    });
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    getMenuInflater().inflate(R.menu.menu_list_animation, menu);
    return true;
}

改造请求

public static List<Task> getTasksData() {
    HttpLoggingInterceptor interceptor = new HttpLoggingInterceptor();
    interceptor.setLevel(HttpLoggingInterceptor.Level.BODY);
    OkHttpClient client = new OkHttpClient.Builder().addInterceptor(interceptor).build();

    Gson gson = new GsonBuilder()
            .setDateFormat("yyyy-MM-dd HH:mm:ss")
            .create();

    Retrofit retrofit= new Retrofit.Builder()
            .baseUrl("http://10.0.2.2/index.php/")
            .addConverterFactory(GsonConverterFactory.create(gson))
            .client(client)
            .build();

    TasksApi taskAPI =retrofit.create(TasksApi.class);
    Call<List<Task>> call = taskAPI.getAllTasks();

    call.enqueue(new Callback<List<Task>>() {
        @Override
        public void onResponse(Call<List<Task>> call, Response<List<Task>> response) {
            items = response.body();
        }
        @Override
        public void onFailure(Call<List<Task>> call, Throwable t) {
        }
    });
    return items;
}

适配器

public class AdapterTasks extends RecyclerView.Adapter<RecyclerView.ViewHolder> {

private List<Task> items;
private Context ctx;

private OnItemClickListener mOnItemClickListener;
private int animation_type = 0;

public interface OnItemClickListener {
    void onItemClick(View view, Task obj, int position);
}

public void setOnItemClickListener(final OnItemClickListener mItemClickListener) {
    this.mOnItemClickListener = mItemClickListener;
}

public AdapterTasks(Context context, List<Task> items, int animation_type) {
    this.items = DataGenerator.getTasksData();
    this.items.addAll(DataGenerator.getTasksData());
    ctx = context;
    this.animation_type = animation_type;
}

public class OriginalViewHolder extends RecyclerView.ViewHolder {
    public View lyt_parent;
    public TextView laikas;
    public TextView klientas;
    public TextView darbas;
    public TextView komentaras;
    public Button atlikta;


    public OriginalViewHolder(View v) {
        super(v);
        laikas = (TextView) v.findViewById(R.id.laikas);
        klientas = (TextView) v.findViewById(R.id.name);
        lyt_parent = (View) v.findViewById(R.id.lyt_parent);
        darbas = (TextView) v.findViewById(R.id.darbas);
        komentaras = (TextView) v.findViewById(R.id.komentaras);
        atlikta = (Button) v.findViewById(R.id.atlikta);

    }
}

@Override
public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    RecyclerView.ViewHolder vh;
    View v = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_task, parent, false);
    vh = new OriginalViewHolder(v);
    return vh;
}

// Replace the contents of a view (invoked by the layout manager)
@Override
public void onBindViewHolder(RecyclerView.ViewHolder holder, final int position) {
    Log.e("onBindViewHolder", "onBindViewHolder : " + position);
    if (holder instanceof OriginalViewHolder) {
        OriginalViewHolder view = (OriginalViewHolder) holder;

        Task t = items.get(position);
        view.laikas.setText((CharSequence) t.AtlikData);
        view.klientas.setText(t.KlientasID);
        view.darbas.setText(t.VeiksmoID);
        view.komentaras.setText(t.Komentaras);
        view.lyt_parent.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                if (mOnItemClickListener != null) {
                    mOnItemClickListener.onItemClick(view, items.get(position), position);
                }
            }
        });
        setAnimation(view.itemView, position);
    }
}

@Override
public void onAttachedToRecyclerView(RecyclerView recyclerView) {
    recyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
        @Override
        public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
            on_attach = false;
            super.onScrollStateChanged(recyclerView, newState);
        }
    });
    super.onAttachedToRecyclerView(recyclerView);
}

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

private int lastPosition = -1;
private boolean on_attach = true;

private void setAnimation(View view, int position) {
    if (position > lastPosition) {
        ItemAnimation.animate(view, on_attach ? position : -1, animation_type);
        lastPosition = position;
    }
}

}

Answer 1

您的方法是异步的，因此onResponse中的代码将在您的getTaskData方法已经返回一个空列表之后运行。 您需要修改程序流程以适应这种情况。

这是一个示例，说明如何定义自己的自定义回调来处理该问题，首先将 RecyclerView 设置为空，然后在数据到达后添加数据。

第 1 步：在某处定义接口（例如在活动或改造请求类中）

interface OnTasksRetrieved {
    void getResult(List<Task> result);
}

第 2 步：更改您的getTasksData方法以采用实现该接口的回调而不是返回列表

public static void getTasksData(OnTasksRetrieved callback) {
    //...
    call.enqueue(new Callback<List<Task>>() {
        @Override
        public void onResponse(Call<List<Task>> call, Response<List<Task>> response) {
            // Call your callback once you have retrieved the data
            callback.getResult(response.body());
        }
        @Override
        public void onFailure(Call<List<Task>> call, Throwable t) {
        }
    });

    // do not return anything
}

第 3 步：当您在onCreate中启动异步调用时，创建回调接口的实例以传递给它以处理结果

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_list_animation);
    parent_view = findViewById(android.R.id.content);
    initComponent();
    
    // start the async fetch here - it won't finish until
    // later in the future, when it will call the callback code
    // below to update the RecyclerView data
    getTasksData(
        new OnTasksRetrieved() {
            @Override
            public void getResult(List<Task> result) {
                // The code in here runs much later in the future - the adapter
                // will already have been set up, but will be empty.
                myAdapter.setItems(result); // add this method to the adapter
            }
        }
    );
}

您将需要修改适配器，使其不将 List 作为输入，而是有一个类似这样的setItems方法，一旦检索到数据就会调用该方法：

private List<Task> items = new ArrayList<>();

public AdapterTasks(Context context,  int animation_type) {
    ctx = context;
    this.animation_type = animation_type;
}

public void setItems(List<Task> data) {
    items.clear();
    items.addAll(data);
    notifyDataSetChanged();
}