无法从嵌套的Firebase数据库中捕获值

Question

我的firebase数据库结构如下：

基本上，我试图捕捉＆＃34;回答的价值。＆＃34;我正在运行以下代码：

 public void onDataChange(DataSnapshot dataSnapshot) {
                        //should dump all of poll creators items in the following section of the current user
                        Log.v("DataSnap", dataSnapshot.toString());
                        Log.v("DataSnap", dataSnapshot.child(USER_ID_LABEL).getValue().toString());
                        ArrayList<String > mPollAnswers = new ArrayList<>();
                        for (DataSnapshot y : dataSnapshot.child(ANSWERS_LABEL).getChildren()){
                            Log.v("ANSWER", y.getValue().toString());
                        }

不幸的是，它正在返回＆＃34;投票数＆＃34;并且＆＃34;回答，＆＃34;当我严格要求答案的价值时：

Answer 1

如果您可以访问顶级键，例如L3l1 ......，＆＃34;答案＆＃34;和＆＃34; 1＆＃34;，firebase将以Hashmap<String, Object>的形式返回结果对象，其中Object可以是任何内容。

FirebaseDatabase firebaseDatabase = FirebaseDatabase.getInstance();
    firebaseDatabase.getReference("<top-level-key>")
            .child("L3l1...")
            .child("answers")
            .child("1")
            .addValueEventListener(new ValueEventListener() {
                @Override
                public void onDataChange(DataSnapshot dataSnapshot) {
                    //Returns a hashmap with keys of type answer and vote_count
                    Object value = dataSnapshot.getValue(); /
                    Object o = ((HashMap) value).get("answer");
                    String s = "";
                }

                @Override
                public void onCancelled(DatabaseError databaseError) {

                }
            });

1. 更优雅的解决方案 要简化事物，请创建一个Answer类并将其强制转换为数据快照。

   public class Answer {
       private int vote_count;
       private String answer;
   
       public Answer() {
       }
   
       public int getVote_count() {
           return vote_count;
       }
   
       public void setVote_count(int vote_count) {
           this.vote_count = vote_count;
       }
   
       public String getAnswer() {
           return answer;
       }
   
       public void setAnswer(String answer) {
           this.answer = answer;
       }
   }
   

在您的活动中或您调用firebase的任何地方：

//In your Activity or Fragment or wherever you call Firebase
        firebaseDatabase.getReference("<top-level-key>")
            .child("L13a")
            .child("answers")
            .child("1")
            .addValueEventListener(new ValueEventListener() {
                @Override
                public void onDataChange(DataSnapshot dataSnapshot) {

                    Answer value = dataSnapshot.getValue(Answer.class);
                    //value.getAnswer() = "rstrrs"
                    //value.getVote_Count() = 0
                }

                @Override
                public void onCancelled(DatabaseError databaseError) {

                }
            });