Android 微調器未顯示所選文本

Question

我將數據從 Firestore 數據庫中提取到 ArrayList 中，然后將這些對象加載到微調器中。 當我打開微調器進行選擇時，所有對象都會正確顯示，但是當您從微調器中打開 select 和 object 時，微調器保持空白並且不顯示任何文本。 我已經嘗試添加adapter.notifyDataSetChanged(); 並且我也嘗試更改文本的顏色，因為我在其他地方看到了這個建議，但兩種解決方案都沒有奏效。

這是我的 java 文件：

public class AdminEditor extends AppCompatActivity {

    FirebaseFirestore db;
    CollectionReference usersRef;

    ArrayList<UserItem> users;

    Spinner spinnerUser;
    Button btnGetData;
    TextView txtTest;

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

        //Set up FireStore and references
        db = FirebaseFirestore.getInstance();
        usersRef = db.collection("users");

        //Set up resources
        txtTest = findViewById(R.id.txtTest);
        spinnerUser = findViewById(R.id.spinnerUser);
        btnGetData = findViewById(R.id.btnGetData);

        users = new ArrayList<UserItem>();

        loadUsers();
        updateSpinner();

    }

    public void loadUsers() {
        usersRef.get()//Get entire users collection
                .addOnSuccessListener(new OnSuccessListener<QuerySnapshot>() {
                    @Override
                    public void onSuccess(QuerySnapshot queryDocumentSnapshots) {
                        for (QueryDocumentSnapshot documentSnapshot : queryDocumentSnapshots) {
                            users.add((UserItem)documentSnapshot.toObject(UserItem.class));//Add each user from the collection to the arraylist
                        }
                    }
                });
    }

    //To fill spinners with data
    public void updateSpinner() {
        ArrayAdapter<UserItem> adapter = new ArrayAdapter<UserItem>(this, android.R.layout.simple_spinner_item, users);
        adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        spinnerUser.setAdapter(adapter);
        spinnerUser.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
            @Override
            public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
                UserItem user = (UserItem) parent.getSelectedItem();
            }

            @Override
            public void onNothingSelected(AdapterView<?> parent) {
            }
        });
    }
} 

這是 xml 文件：

<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=".AdminEditor">

    <Spinner
        android:id="@+id/spinnerUser"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="128dp"
        android:spinnerMode="dropdown"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <Button
        android:id="@+id/btnGetData"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="28dp"
        android:text="Get Data"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.498"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/spinnerUser" />

    <TextView
        android:id="@+id/txtTest"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/btnGetData" />

</androidx.constraintlayout.widget.ConstraintLayout>```

Thanks for your help

Answer 1

每當從 Firebase 完全接收到用戶時更新您的微調器，因此updateSpinner()的調用轉移到usersRef.get().addOnSuccessListener並將其從onCreate()方法中刪除

public void loadUsers() {
    usersRef.get()//Get entire users collection
            .addOnSuccessListener(new OnSuccessListener<QuerySnapshot>() {
                @Override
                public void onSuccess(QuerySnapshot queryDocumentSnapshots) {
                    for (QueryDocumentSnapshot documentSnapshot : queryDocumentSnapshots) {
                        users.add((UserItem)documentSnapshot.toObject(UserItem.class));//Add each user from the collection to the arraylist
                    }
                    updateSpinner();
                }
            });