java - Spinner Widget 将不会显示所选文本

Question

我正在创建一个使用 Cloud Firestore 的 Android 应用。数据库中有一个文档，其中包含我需要在 Android 应用程序上显示的名称。问题是，虽然我使用的 Spinner 小部件正确填充，但该小部件不显示所选文本

我已经尝试更改微调器的背景和文本颜色，但无济于事( Spinner does not show selected value )

旋转器 XML:

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.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=".MainActivity">

    <Button
        android:id="@+id/button2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginEnd="168dp"
        android:layout_marginBottom="416dp"
        android:onClick="loginButton"
        android:text="Login"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent" />

    <Spinner
        android:id="@+id/spinner"
        android:layout_width="291dp"
        android:layout_height="55dp"
        android:layout_marginEnd="60dp"
        android:layout_marginBottom="304dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent" />

</android.support.constraint.ConstraintLayout>

Java 代码:

public class MainActivity extends AppCompatActivity{
    List<String> names;
    Spinner spinner;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        spinner = findViewById(R.id.spinner);
        names = new ArrayList<String>();
        FirebaseFirestore db = FirebaseFirestore.getInstance();
        db.collection("Investors").document("InvestorNames").get().addOnSuccessListener(new OnSuccessListener<DocumentSnapshot>() {
            @Override
            public void onSuccess(DocumentSnapshot documentSnapshot) {
                Map<String, Object> map = documentSnapshot.getData();
                for(Map.Entry<String, Object> entry: map.entrySet()){
                    names.add((String)entry.getValue());
                }
            }
        }).addOnFailureListener(new OnFailureListener() {
            @Override
            public void onFailure(@NonNull Exception e) {

            }
        });
        ArrayAdapter<String> dataAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, names);
        dataAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        spinner.setAdapter(dataAdapter);
    }

实际输出: 从微调器中选择值后，它不会显示任何内容，不会出现任何文本

预期行为: 选择微调器中的值后，微调器应显示所选文本

Answer 1

    public class MainActivity extends AppCompatActivity implements AdapterView.OnItemSelectedListener {

    spinner.setOnItemSelectedListener(this);

            // Spinner Drop down elements
           **Populate your List Here** 
     List<String> categories = new ArrayList<String>();
categories.add('');
            // Creating adapter for spinner
            ArrayAdapter<String> dataAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_spinner_item, categories);

            // Drop down layout style - list view with radio button
            dataAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);

            // attaching data adapter to spinner
            spinner.setAdapter(dataAdapter);

      @Override
        public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
            // On selecting a spinner item
            String item = parent.getItemAtPosition(position).toString();
     view.setSelection(int)
            // Showing selected spinner item
            Toast.makeText(parent.getContext(), "Selected: " + item, Toast.LENGTH_LONG).show();

        }

        public void onNothingSelected(AdapterView<?> arg0) {
            // TODO Auto-generated method stub

        }


    }