检索值firebase有困难

Question

所以我在从我的firebase数据库中检索值时遇到了一个问题。基本上，我希望获得与"username“键相关联的值。但是，我当前的代码只返回任何内容。当我通过省略.child(“用户名”)来更改代码时，dataSnapshotTwo同时包含电子邮件和用户名。我在这里做错了什么？

这是我的代码:唯一用户is是随机字符的字符串，如"cUkHiXwIaXOqigeoRPuh3Yc9oau2“

public void sendFriendRequest(final String userID){
    mDatabase.child("Users").child(uniqueUserID).child("username")
            .addListenerForSingleValueEvent(new ValueEventListener() {
                @Override
                public void onDataChange(DataSnapshot dataSnapshotTwo) {

                        for (DataSnapshot miniSnapshot : dataSnapshotTwo.getChildren()) {
                            String currentUserName = (String) miniSnapshot.getValue();
                            mDatabase.child("Users").child(userID).child("Requests").child(uniqueUserID).setValue(currentUserName);

                    }
                }

                @Override
                public void onCancelled(DatabaseError firebaseError) {
                    Log.e("MainActivity", "onCancelled", firebaseError.toException());
                }
            });

}

这是我的数据库结构：

{"Users" : 
{
    "User_1" : {
           "Called" : {
                "Fritz" : 1
            },

            "City" : "Groningen",

            "Friends" : {
                  "Fritz" : 50,

                  "Jos" : 0


            "Requests" : {

                "zuipmaat_1" : 0


            "email" : "b@hotmail.com",

            "username" : "Bert"



    "cUkHiXwIaXOqigeoRPuh3Yc9oau2" : {

            "Requests" : {

                "cUkHiXwIaXOqigeoRPuh3Yc9oau2" : "Tommie"


            "email" : "t2@live.nl",

            "username" : "Tommie"



    "jAYc9IzcBRRuXZCxYEncEIRrPw72" : {

            "Requests" : {

                "cUkHiXwIaXOqigeoRPuh3Yc9oau2" : "Tommie "


            "email" : "t@hotmail.com",

            "username" : "Tom"

Answer 1

要获取用户名，请使用以下代码：

public void sendFriendRequest(final String userID){
    mDatabase.child("Users").child(uniqueUserID).child("username").addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshotTwo) {
            String currentUserName = dataSnapshotTwo.getValue(String.class);
            Log.d("TAG", currentUserName);
        }

        @Override
        public void onCancelled(DatabaseError firebaseError) {
            Log.e("MainActivity", "onCancelled", firebaseError.toException());
        }
    });
}

正如您可能看到的，我删除了那个for循环，因为不需要它。

Answer 2

这个看起来更漂亮

 {
 "Users": {
  "User_1": {
     "Called": {
        "Fritz": 1
     },
     "City": "Groningen",
     "Friends": {
        "Fritz": 50,
        "Jos": 0
     },
     "Requests": {
        "zuipmaat_1": 0
     },
     "email": "b@hotmail.com",
     "username": "Bert"
  },
  "cUkHiXwIaXOqigeoRPuh3Yc9oau2": {
     "Requests": {
        "cUkHiXwIaXOqigeoRPuh3Yc9oau2": "Tommie"
     },
     "email": "t@live.nl",
     "username": "Tommie"
  },
  "jAYc9IzcBRRuXZCxYEncEIRrPw72": {
     "Requests": {
        "cUkHiXwIaXOqigeoRPuh3Yc9oau2": "Tommie"
     },
     "email": "tom@hotmail.com",
     "username": "Tom"
  }
 }
}

Answer 3

如果我没弄错你的意图...

首先，更好地处理对象。

public class User {

    public Called Called;
    public String City;
    public ArrayList<Friend> Friends;
    public ArrayList<Requests> Requests;
    public String email;
    public String username;

    public class Called{
        public String name;
        public int sum;
    }

    public class Friend{
        public String name;
        public int sum;
    }

    public class Requests{
        public String name;
        public int sum;
    }
}

其次，尝试更新/插入all对象

User user = new User();
user.City = ..... /*populate the object*/

database.getReference("Users").push().setValue(user); // generate the user Id automatically 

或

database.getReference("Users").child(userID).setValue(user); // generate your own user Id 

第三，检索数据

 public void sendFriendRequest(final String userID) {
    mDatabase.child("Users").addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshotTwo) {

            for (DataSnapshot miniSnapshot : dataSnapshotTwo.getChildren()) {
                User user = (User) miniSnapshot.getValue();
                System.out.println(user.username); // print the username
            }
        }

        @Override
        public void onCancelled(DatabaseError firebaseError) {
            Log.e("MainActivity", "onCancelled", firebaseError.toException());
        }
    });
}

永远不要测试它。希望这能对你有所帮助。