firebase - Flutter Firebase Realtime数据库获取单个数据查询结果值null

Question

路径=用户 token

uid = W9aafYsF6cOPr1sMLKlnFEUcNNR2

userTokens/W9aafYsF6cOPr1sMLKlnFEUcNNR2

我想带下划线的区域在图片中。我应该如何使用Firebase Realtime Database编写查询？

结果变量为null。

import 'package:firebase_database/firebase_database.dart';
import 'package:flutter/cupertino.dart';

class NotificationServiceTools {
  static final FirebaseDatabase firebaseDatabase = new FirebaseDatabase();

  static Future<String> getUserTokens({@required String uid}) async {
    final String result =
        (await firebaseDatabase.reference().child("userTokens/$uid").once())
            .value
            .toString();
    print("result: $result");

    return result;
  }
}

该函数称为:

print(receiver);
token = await NotificationServiceTools.getUserTokens(uid: receiver);
print("token : " + token);

日志:

I/flutter ( 9447): vUpgi1QyU1UxK7tCJ5rcJqnOdaO2
I/flutter ( 9447): result : null
I/flutter ( 9447): token : null

Answer 1

试试这个，

String result;
await firebaseDatabase.instance
.reference()
.child('userTokens/$uid')
.once()
.then((snapshot){result=snapshot.value;});