无法将数据从QueryDocumentSnapshot添加到Android Studio中的addOnCompleteListener中的ArrayList

Question

我从addOnCompleteListener内的FirebaseFireStore数据库中成功获取了数据，并且可以使用Toast显示数据，但无法使用arrayList.add（object）方法将数据添加到ArrayList中。代码完成后，它将数组大小显示为0。：（

代码如下：

private void getDataFromFireBase()
{
    try
    {



        final SimpleDateFormat dateFormat= new SimpleDateFormat("MMM d, h:mm a");
        objFirebaseFirestore.collection(COL_THOUGHTS).get().
                addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
                    @Override
                    public void onComplete(@NonNull Task<QuerySnapshot> task) {
                            if(task.isComplete())
                            {
                                for(QueryDocumentSnapshot data:task.getResult())
                                {
                                    Timestamp timestampValue=data.getTimestamp("timestamp");
                                    Toast.makeText(MainActivity.this, "Fetching data", Toast.LENGTH_SHORT).show();
                                    /*Toast.makeText(MainActivity.this, data.getString("username")
                                            +"\n"+data.getString("category")
                                            +"\n"+data.getString("thoughtText")
                                            +"\n"+data.getId()
                                            +"\n"+data.getLong("numOfLikes")
                                            +"\n"+ dateFormat.format(timestampValue.toDate()), Toast.LENGTH_SHORT).show();*/
                                    //Toast.makeText(MainActivity.this, data.getString("username"), Toast.LENGTH_SHORT).show();



                                    String userNameDummy=data.getString("username");
                                    String categoryDummy=data.getString("category");

                                    String thoughtTextDummy=data.getString("thoughtText");
                                    String idDummy=data.getId();

                                    String dateDummy=dateFormat.format(timestampValue.toDate());
                                    long numOfLikesDummy=data.getLong("numOfLikes");

                                    /*thoughtsModelClassArrayList.add(new ThoughtsModelClass(
                                            userNameDummy,
                                            categoryDummy,
                                            thoughtTextDummy,
                                            idDummy,
                                            dateDummy,
                                            0,
                                             numOfLikesDummy
                                    ));*/
                                    ThoughtsModelClass obj=new ThoughtsModelClass(userNameDummy,categoryDummy,
                                            thoughtTextDummy,idDummy,dateDummy,0,numOfLikesDummy) ;
                                    thoughtsModelClassArrayList.add(obj);
                                    //Toast.makeText(MainActivity.this, thoughtsModelClassArrayList.size(), Toast.LENGTH_SHORT).show();
                                }
                            }
                            else
                            {
                                Toast.makeText(MainActivity.this, task.getException().getMessage(), Toast.LENGTH_SHORT).show();
                            }
                    }
                });



    }
    catch (Exception e)
    {
        Toast.makeText(this, "getDataFromFireBase:"+e.getMessage(), Toast.LENGTH_SHORT).show();
    }
}