从Fire base数据库检索的数据显示在微调器的下拉列表中，但未将所选项目设置为微调器

Question

这是我的主要活动。还提供XML文件。我正在微调器中从Fire base数据库检索数据。它是“在下拉菜单中查看”，但未将所选项目设置为Spinner。在主要活动中使用showFacultySpinner类从Firebase检索数据。如果有人也要检查，我会提供。

public class TestSpinnerAddCourse extends AppCompatActivity implements AdapterView.OnItemSelectedListener {

    DatabaseReference databaseReference;
    showFacultySpinner showFacultySpinner;

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


        databaseReference = FirebaseDatabase.getInstance().getReference();
        showFacultySpinner = new showFacultySpinner(databaseReference);

// Spinner element
        Spinner spinner = (Spinner) findViewById(R.id.spinner);

        // Spinner click listener
        spinner.setOnItemSelectedListener(this);


        // Creating adapter for spinner
        ArrayAdapter<String> dataAdapter = 
            new ArrayAdapter<String>(
                this, 
                android.R.layout.simple_spinner_item, 
                showFacultySpinner.retreive()
            );

        // 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();

        Toast.makeText(parent.getContext(), "Selected: " + item , Toast.LENGTH_LONG).show();
    }


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

    }
}

这是我的XML文件：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:padding="10dip"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"

  >

    <TextView
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="10dip"
        android:text="Category:"
        android:layout_marginBottom="5dp"/>

    <Spinner
        android:id="@+id/spinner"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
       />

</LinearLayout>