java - 检索firebase实时数据库中节点下的所有数据

Question

我有一个 Firebase 实时数据库，想使用该数据制作排行榜。我试图检索“分数”节点中的所有数据，但不确定如何循环以获取所有用户的分数。

数据库结构如下:

我尝试使用的代码是这样的:

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());

    }


});

        }
}

Answer 1

您对 JSON 的了解太深了，正在阅读 /Points/Points。由于该节点不存在，因此您会在 onDataChange 中获得一个空快照。

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: