微调器上的选定项目将不起作用 (ANDROID)

Question

我的数据来自 Firebase 数据库。我成功地将 busNum 填充到 spinner。但我的问题是每当我到达 select 和 busnum 时，我的 spinner 上什么也没有显示。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);

Answer 2

ArrayList<String> issueCategoryArrayList = new ArrayList<String>();
FirebaseDatabase.getInstance().getReference("issue_categories").addListenerForSingleValueEvent(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        for(DataSnapshot dataSnapshot1 : dataSnapshot.getChildren()) {
            issueCategoryArrayList.add(dataSnapshot1.getValue(IssueCategory.class).getTitle());
        }
        spinner = findViewById(R.id.post_category);
        ArrayAdapter<String> dataAdapter = new ArrayAdapter<String>(PostActivity.this,
                android.R.layout.simple_spinner_item, issueCategoryArrayList);
        dataAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        spinner.setAdapter(dataAdapter);;
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {

    }
});

微调器上的选定项目将不起作用 (ANDROID)

selected item on spinner won't work (ANDROID)

java

android

spinner

android-spinner