Question

我正在尝试从FireBase数据库填充ArrayList。在事件侦听器中，ArrayList的大小实际上等于某个数字，但在侦听器之外，值为零。

问题数组的大小值应大于零，因为我正在其中添加元素。请帮助我找出问题所在。我一直在努力解决这个问题。

ArrayList <Question> questions = new ArrayList<Question>();
int totalQuestCount =0;
FirebaseDatabase fDataBase;
DatabaseReference quizRef;


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

    Log.d("QUESTION_SIZE1", String.valueOf(questions.size()));
    fDataBase = FirebaseDatabase.getInstance();
    quizRef = fDataBase.getReference("quizes/quiz1");
    quizRef.keepSynced(true);
    quizRef.addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
            if(dataSnapshot.exists() && dataSnapshot.hasChildren()){
                totalQuestCount=(int)dataSnapshot.getChildrenCount();
                questions.ensureCapacity(totalQuestCount);
                Log.d("QuestionCount", String.valueOf(totalQuestCount));
                for(DataSnapshot data: dataSnapshot.getChildren()){
                    questions.add(data.getValue(Question.class));
                }
                Log.d("QUESTION_SIZE2", String.valueOf(questions.size()));
            }else{
                Log.d("DATASNAP", "DOES NOT EXISTS");
            }
        }

        @Override
        public void onCancelled(@NonNull DatabaseError databaseError) {

        }

    });
    Log.d("QUESTION_SIZE3", String.valueOf(questions.size()));


}
}

Answer 1

在此区块

 for(DataSnapshot data: dataSnapshot.getChildren()){
                questions.add(data.getValue(Question.class));
    }

放入

System.out.println(data.getValue(Question.class));

并检查您是否实际上是从firebase获取数据并将其添加。？

喜欢

 for(DataSnapshot data: dataSnapshot.getChildren()){
                System.out.println(data.getValue(Question.class));
                questions.add(data.getValue(Question.class));
    }

然后让我们知道。

在匿名内部类之外，ArrayList的值不同

1 个答案: