java - 微调器上的选定项目不起作用(ANDROID)

Question

我的数据来自 Firebase 数据库。我成功填充了 busNum到 spinner .但我的问题是每当我必须选择 busnum ，我的 spinner 上没有显示任何内容.这是一些代码。 List<String> busnum = new ArrayList<String>();

busRef =  new Firebase(Config.FIREBASE_URL_BUSNUMBER);
    busRef.addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            for (DataSnapshot postSnapshot : dataSnapshot.getChildren()) {
                busnum.add(postSnapshot.child("busNum").getValue().toString());
            }
        }

        @Override
        public void onCancelled(FirebaseError firebaseError) {
            Toast.makeText(AddDriverActivity.this, "Failed to read data.... " +firebaseError.getMessage(), Toast.LENGTH_SHORT).show();
        }
    });

ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_spinner_item, busnum);
    mSpinBusNum.setPrompt("Select bus number");
    mSpinBusNum.setAdapter(adapter);

@Override
public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
    busNum = parent.getItemAtPosition(position).toString();
}

Answer 1

您必须像这样在数据更改之后设置适配器:

//after onDataChange 
ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,android.R.layout.simple_spinner_item, busnum);
mSpinBusNum.setPrompt("Select bus number");
// Apply the adapter to the spinner
mSpinBusNum.setAdapter(adapter);