计算 RecyclerView 显示的项数并放入一个 TextView

Question

目前，我可以在我的RecyclerView. 我想要做的是计算这些项目中有多少。我的项目保存在CardView. 我不想计算或求和任何特定字段，只想计算实际项目的数量。这是我的代码，我尝试使用getItemCount()方法设置它并将其附加到 TextView 并在 RecyclerView 之外显示。这对我不起作用：

public class COM800s1 extends AppCompatActivity {

private FirebaseFirestore db = FirebaseFirestore.getInstance();

private CollectionReference attendanceRef = db.collection("Attendance");

private AttendanceAdapter adapter;

private Context context;

private TextView attendanceNumbers;

private int counter;

@Override

protected void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);

    setContentView(R.layout.activity_com800s1);

    attendanceNumbers = findViewById(R.id.attendanceNums);

    FloatingActionButton floatingActionButton = findViewById(R.id.button_add_session);

    floatingActionButton.setOnClickListener(new View.OnClickListener() {

        @Override

        public void onClick(View v) {

            startActivity(new Intent(COM800s1.this,NewAttendanceRecord.class));

        }

    });

    setUpRecyclerView();

}

private void setUpRecyclerView() {

    final Query query = attendanceRef.whereEqualTo("sessionID", "5I0PLcpgmwdcjKLYLgkU").orderBy("userEmail", Query.Direction.ASCENDING);

    FirestoreRecyclerOptions<Attendance> options = new FirestoreRecyclerOptions.Builder<Attendance>()

            .setQuery(query, Attendance.class).build();

    adapter = new AttendanceAdapter(options);

    RecyclerView recyclerView = findViewById(R.id.recycler_view);

    recyclerView.setHasFixedSize(true);

    recyclerView.setLayoutManager(new LinearLayoutManager(this));

    recyclerView.setAdapter(adapter);

   //counter = adapter.getItemCount();

   //attendanceNumbers.setText("Currently " +counter+ " students have attended this session");

    new ItemTouchHelper(new ItemTouchHelper.SimpleCallback(0,

            ItemTouchHelper.LEFT | ItemTouchHelper.RIGHT) {

        @Override

        public boolean onMove(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, RecyclerView.ViewHolder target) {

            return false;

        }

Answer 1

如果您试图将counter变量作为全局变量并在回调之外使用它，那将始终是null因为正如@Vinnie 在他的回答中提到的那样，数据尚未完成加载。真正发生的事情是您试图从数据库中获取数据并立即使用它，而counter变量的初始值为0.&nbsp;然后，当从数据库中获取数据完成时，它会更改计数器的值，但不会再次读取。为了解决这个问题，getItemCount()在你的适配器类中使用你的方法的结果将它的值设置为TextView.

Answer 2

如果您想获取您的 recyclerView 列表，只需在您的 recyclerView 适配器中创建一个静态方法，然后在其中返回您的列表。例如：public static List<modelOfYourList> getCount(){&nbsp; &nbsp;return yourAdapterList;}

Answer 3

也许在你的AttendanceAdapter课堂上添加这样的东西？我看了一下FirestoreRecyclerOptions类，它公开了一个getSnapshots()方法。这将返回 a ObservableSnapshotArray，而后者又从 扩展而来Base ObservableSnapshotArray，它公开了一个size()方法。class AttendanceAdapter extends FirestoreRecyclerAdapter<Attendance, AttendanceAdapter.AttendanceHolder>{{&nbsp;&nbsp; &nbsp; private FirestoreRecyclerOptions<Attendance> options;&nbsp; &nbsp; public AttendanceAdapter(@NonNull FirestoreRecyclerOptions<Attendance> options)&nbsp; &nbsp; {&nbsp; &nbsp; &nbsp; &nbsp; super(options);&nbsp; &nbsp; &nbsp; &nbsp; this.options = options;&nbsp; &nbsp; }&nbsp; &nbsp; @Override&nbsp; &nbsp; public int getItemCount()&nbsp; &nbsp; {&nbsp; &nbsp; &nbsp; &nbsp; final int count = options.getSnapshots() != null&nbsp;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; ? options.getSnapshots().size()&nbsp;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; : 0;&nbsp; &nbsp; &nbsp; &nbsp; return count;&nbsp; &nbsp; }