我的微调器被覆盖，同时添加了从Firebase数据库中选择的多个值

Question

I want to get all the values from the courseName and use it to fill the spinner:

databaseReference.addChildEventListener(new ChildEventListener() {
  @Override
  public void onChildAdded(DataSnapshot dataSnapshot, String s) {
    final List<String> courses = new ArrayList<String>();
    for (DataSnapshot courseSnapshot: dataSnapshot.getChildren())
    {
      String courseName = courseSnapshot.getValue(String.class);
      courses.add(courseName);
    }

    Spinner spinnerCourse = findViewById(R.id.spinnerCourse);
    ArrayAdapter<String> courseAdapter = new ArrayAdapter<String>(AddSubject.this,android.R.layout.simple_spinner_item, courses);

    courseAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
    spinnerCourse.setAdapter(courseAdapter);
  }
}

Answer 1

You need to clear your list first then bind it use clear() method like below

    databaseReference.addChildEventListener(new ChildEventListener() {
    @Override
    public void onChildAdded(DataSnapshot dataSnapshot, String s) 
    {
      final List<String> courses = new ArrayList<String>();
      courses.clear();
      for (DataSnapshot courseSnapshot: dataSnapshot.getChildren()) 
      {
          String courseName = courseSnapshot.getValue(String.class);
          courses.add(courseName);
      }
      Spinner spinnerCourse = findViewById(R.id.spinnerCourse);
      ArrayAdapter<String> courseAdapter = new ArrayAdapter<String>(AddSubject.this,android.R.layout.simple_spinner_item, courses);
      courseAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
      spinnerCourse.setAdapter(courseAdapter);
    } 
   }