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。
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());
}
});
}
}
最佳答案
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:
关于java - 检索firebase实时数据库中节点下的所有数据,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/60216366/