检索Firebase实时数据库中节点下的所有数据 [英] Retrieve all data under node in firebase realtime database

问题描述

我有一个firebase实时数据库，想使用这些数据来排行榜.我试图检索分数"节点中的所有数据，但不确定如何循环获取所有用户的分数.

I have a firebase realtime database and want to use the data to make a leaderboard. Im trying to retrieve all the data in my Scores node but am not sure how to loop through to get the scores of all users.

数据库结构如下:

我尝试使用的代码是这样:

The code I have tried to use is this:

package com.example.securityapp;

import androidx.appcompat.app.AppCompatActivity;

import android.nfc.Tag;
import android.os.Bundle;
import android.util.Log;
import android.widget.TextView;

import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseUser;
import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.google.firebase.database.Query;
import com.google.firebase.database.ValueEventListener;

import static java.lang.System.in;

public class leaderboard extends AppCompatActivity {

    DatabaseReference databaseUsers;
    FirebaseDatabase database = FirebaseDatabase.getInstance();
    FirebaseAuth mAuth;
    TextView score;
    private static final String TAG = "leaderboard";



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

        databaseUsers = database.getReference().child("Scores");
        mAuth = FirebaseAuth.getInstance();
        FirebaseUser user = mAuth.getCurrentUser();
        score = (TextView) findViewById(R.id.leaderboard_score);


        databaseUsers.child("Scores").addValueEventListener(new ValueEventListener() {
            public void onDataChange(DataSnapshot dataSnapshot) {
                for (DataSnapshot snapshot : dataSnapshot.getChildren()) {
                        System.out.println("The scores are " + dataSnapshot.child("Points").getValue().toString());
                    }
                }


            @Override
            public void onCancelled(DatabaseError databaseError) {
             // Getting Post failed, log a message
             Log.w(TAG, "loadPost:onCancelled", databaseError.toException());

    }


});

        }
}

推荐答案

您对JSON的了解太高了，正在阅读/Points/Points.由于该节点不存在，因此您在onDataChange中会得到一个空快照.

You're going one level too deep into your JSON and are reading /Points/Points. Since that node doesn't exist, you get an empty snapshot in your onDataChange.

database.getReference().child("Scores").addValueEventListener(new ValueEventListener() {
    public void onDataChange(DataSnapshot dataSnapshot) {
        for (DataSnapshot snapshot : dataSnapshot.getChildren()) {
            Log.i(TAG, "The scores are " + dataSnapshot.child("Points").getValue(Long.class));
        }
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {
        Log.w(TAG, "loadPost:onCancelled", databaseError.toException());
    }
});

返回值的新代码:

public class leaderboard extends AppCompatActivity {

    DatabaseReference databaseUsers;
    FirebaseDatabase database = FirebaseDatabase.getInstance();
    FirebaseAuth mAuth;
    TextView score;
    private static final String TAG = "leaderboard";



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

        mAuth = FirebaseAuth.getInstance();
        FirebaseUser user = mAuth.getCurrentUser();
        score = (TextView) findViewById(R.id.tableText);


        database.getReference().child("Scores").addValueEventListener(new ValueEventListener() {
            public void onDataChange(DataSnapshot dataSnapshot) {
                for (DataSnapshot snapshot : dataSnapshot.getChildren()) {
                        System.out.println("The score is: " + snapshot.toString());
                        score.setText(snapshot.toString());
                    }
                }


            @Override
            public void onCancelled(DatabaseError databaseError) {
             // Getting Post failed, log a message
             Log.w(TAG, "loadPost:onCancelled", databaseError.toException());

    }


});

        }
}

这是我的进步:

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