Question

我有一个ArrayList，该列表从改造中获取数据及其工作正常。问题是当我尝试将列表发送到RecyclerView适配器时，它是空的！有什么想法吗？

这是活动

public class ToDoRecycler extends AppCompatActivity {
    RecyclerView todoRecyclerView;

    private RecyclerView.Adapter todoAdapter;
    private RecyclerView.LayoutManager todoLayoutManager;
    public List<ToDo>results;

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


        todoRecyclerView = (RecyclerView)findViewById(R.id.todoRecyclerView);
        todoRecyclerView.setHasFixedSize(true);
        results= new ArrayList<ToDo>();
        todoLayoutManager = new LinearLayoutManager(this);
        todoRecyclerView.setLayoutManager(todoLayoutManager);
        todoRecyclerView.setAdapter(todoAdapter);
        todoAdapter = new TodoRecyclerAdapter(this,results);
        getRetrofitObject();
        FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent = new Intent(ToDoRecycler.this,AddToDo.class);
                startActivity(intent);
            }});}

   public void getRetrofitObject() {
        Retrofit retrofit = new Retrofit.Builder()
                .baseUrl(BASE_URL)
                .addConverterFactory(GsonConverterFactory.create())
                .build();
        APIService service = retrofit.create(APIService.class);
        Call<Result> call = service.getresults();
        call.enqueue(new Callback<Result>() {
            @Override
            public void onResponse(Call<Result> call, Response<Result> response) {
                results = response.body().getResults();
            }
            @Override
            public void onFailure(Call<Result> call, Throwable t) {
                Log.d("onFailure", t.toString());
            }});}
}

适配器

public class TodoRecyclerAdapter  extends RecyclerView.Adapter<TodoRecyclerAdapter.ViewHolder> {
static List<ToDo> todoResults;
static Context context;
List<ToDo>results;
public TodoRecyclerAdapter(List<ToDo> results) {
    this.todoResults = results;
}
@Override
public TodoRecyclerAdapter.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    View itemLayoutView = LayoutInflater.from(parent.getContext()).inflate(R.layout.todo_items, null);
    ViewHolder viewHolder = new ViewHolder(itemLayoutView);
    return viewHolder;
}
@Override
public void onBindViewHolder(final TodoRecyclerAdapter.ViewHolder holder, final int position) {


}

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


public static class ViewHolder extends RecyclerView.ViewHolder {
    public TextView todoTitle;

    public ViewHolder(View itemLayoutView) {
        super(itemLayoutView);
        todoTitle = (TextView) itemLayoutView.findViewById(R.id.todo_title);
    }
}
}

Answer 1

替换这两行

todoRecyclerView.setAdapter(todoAdapter);
todoAdapter = new TodoRecyclerAdapter(this,results);

到此：

todoAdapter = new TodoRecyclerAdapter(this,results);
todoRecyclerView.setAdapter(todoAdapter);

Answer 2

首先构建适配器，然后将适配器添加到RecyclerView

todoAdapter = new TodoRecyclerAdapter(this,results);
todoRecyclerView.setAdapter(todoAdapter);

然后，您需要通知适配器您正在引用的数据集中的更改

public void getRetrofitObject() {
    Retrofit retrofit = new Retrofit.Builder()
            .baseUrl(BASE_URL)
            .addConverterFactory(GsonConverterFactory.create())
            .build();
    APIService service = retrofit.create(APIService.class);
    Call<Result> call = service.getresults();
    call.enqueue(new Callback<Result>() {
        @Override
        public void onResponse(Call<Result> call, Response<Result> response) {
            results = response.body().getResults();
            // Call notifyDataSetChanged here 
            todoAdapter.notifyDataSetChanged();
        }
        @Override
        public void onFailure(Call<Result> call, Throwable t) {
            Log.d("onFailure", t.toString());
        }});}

<强>更新

因此，在第一次设置results时，显然是null，因为其中没有数据。您需要在TodoRecyclerAdapter中处理此问题。您只需检查null函数中的getCount值，然后像这样返回0

public int getCount() {
    if(results != null) return results.size();
    else return 0;
}

Answer 3

问题是您在改造结果之前创建/调用适配器......！

您应该等待结果，当您得到结果时，初始化并将适配器设置为回调中的recyclerview ...！

使用以下代码获取帮助，

    call.enqueue(new Callback<Result>() {
                @Override
                public void onResponse(Call<Result> call, Response<Result> response) {
                    results = response.body().getResults();
 todoRecyclerView.setAdapter(new TodoRecyclerAdapter(this,results));               
}
                @Override
                public void onFailure(Call<Result> call, Throwable t) {
                    Log.d("onFailure", t.toString());

                }});}

并从onCreate（）方法

中删除适配器初始化

<强>更新您的活动类应如下所示，

public class ToDoRecycler extends AppCompatActivity {
    RecyclerView todoRecyclerView;

    private RecyclerView.Adapter todoAdapter;
    private RecyclerView.LayoutManager todoLayoutManager;
    public List<ToDo>results;

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


        todoRecyclerView = (RecyclerView)findViewById(R.id.todoRecyclerView);
        todoRecyclerView.setHasFixedSize(true);
        results= new ArrayList<ToDo>();
        todoLayoutManager = new LinearLayoutManager(this);
        todoRecyclerView.setLayoutManager(todoLayoutManager);
        getRetrofitObject();
        FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent = new Intent(ToDoRecycler.this,AddToDo.class);
                startActivity(intent);
            }});}
}

   public void getRetrofitObject() {
        Retrofit retrofit = new Retrofit.Builder()
                .baseUrl(BASE_URL)
                .addConverterFactory(GsonConverterFactory.create())
                .build();
        APIService service = retrofit.create(APIService.class);
        Call<Result> call = service.getresults();
        call.enqueue(new Callback<Result>() {
            @Override
            public void onResponse(Call<Result> call, Response<Result> response) {
                results = response.body().getResults();
                todoRecyclerView.setAdapter(new TodoRecyclerAdapter(ActivityName.this,results));    
            }
            @Override
            public void onFailure(Call<Result> call, Throwable t) {
                Log.d("onFailure", t.toString());
            }});}

}

Answer 4

看起来你的onBindViewHolder方法缺少一个实现，你的ViewHolder构造函数不会返回一个ViewHolder ..

无法将列表发送到Recycler View适配器Android

4 个答案: