java - 无法从嵌套 Firebase 数据库获取值

Question

我的 Firebase 数据库结构如下:

本质上，我试图捕捉“答案”的值(value)。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，当我严格想要答案的值时，它同时返回“票数”和“答案”:

Answer 1

如果您有权访问顶级键，例如 L3l1...、“answers”和“1”，Firebase 将以 Hashmap<String, Object> 的形式返回结果对象。哪里Object可以是任何东西。

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) {

                }
            });

更优雅的解决方案为了简化事情，创建一个 Answer类并将其转换到数据快照。

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 Activity 中或您调用 firebase 的任何位置:

//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) {

                }
            });