卡片视图未出现在 RecyclerView 中

Question

我正在构建一个连接到 REST API 并检索数据库中所有员工的应用程序。该应用程序使用 RecyclerView 显示在 CardView 中带回的所有员工。问题是 RecyclerView 中没有出现任何内容，并且有从 REST API 返回的数据。它是一个 Android 应用程序，使用 Java 构建，操作系统使用 Pie。该项目是使用基本活动模板创建的。我的活动课public class ViewAllEmployees extends AppCompatActivity {    private List<Employee> employees;    private RecyclerView rcView;    private EmployeeAdapter adapter;    private Context context;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_view_all_employees);        Toolbar toolbar = findViewById(R.id.toolbar);        setSupportActionBar(toolbar);        context = this;        getSupportActionBar().setDisplayHomeAsUpEnabled(true);        FetchEmployeesTask async = new FetchEmployeesTask(new AsyncResponse() {            @Override            public void processFinished(List<Employee> output) {                Log.i("Async", "Finished");            }        });        async.execute();        rcView = findViewById(R.id.rcView);        adapter = new EmployeeAdapter(context, employees);        rcView.setAdapter(adapter);        rcView.setLayoutManager(new LinearLayoutManager(context));    }    private class FetchEmployeesTask extends AsyncTask<Void, Void, List<Employee>> {        public AsyncResponse delegate = null;        public  FetchEmployeesTask(AsyncResponse asyncResponse){            delegate = asyncResponse;        }        @Override        protected List<Employee> doInBackground(Void... voids) {            return new APIHelper().fetchItems();        }        @Override        protected void onPostExecute(List<Employee> items) {            employees = items;            delegate.processFinished(items);        }    }    public interface AsyncResponse{        void processFinished(List<Employee> output);    }

Answer 1

您必须在填充阵列列表后通知您的适配器。初始化您的员工数组列表变量，然后执行：

private class FetchEmployeesTask extends AsyncTask<Void, Void, List<Employee>> {

    public AsyncResponse delegate = null;

    public  FetchEmployeesTask(AsyncResponse asyncResponse){

        delegate = asyncResponse;

    }

    @Override

    protected List<Employee> doInBackground(Void... voids) {

        return new APIHelper().fetchItems();

    }

    @Override

    protected void onPostExecute(List<Employee> items) {

        employees.addAll(items);

        adapter.notifyDataSetChanged();

        delegate.processFinished(items);

    }

}

Answer 2

FetchEmployeesTask async = new FetchEmployeesTask(new AsyncResponse() {

    @Override

    public void processFinished(List<Employee> output) {

        Log.i("Async", "Finished");

        employees.addAll(items);

        adapter.notifyDataSetChanged();

    }

});