fcm firebase 函数未定义值 - 第一次尝试，已定义 - 第二次尝试

Question

我有一个 Android 应用程序，我打算通过 fcm 实现发送通知。我已经为它编写了下面的 Javascript 代码，但是当我第一次尝试关注某人时，这些值是未定义的，但是，第二次它可以正常工作...

Undefined first attempt

Defined second attempt

我尝试将这三个函数嵌套在一个函数中，还尝试在本地声明变量但未解决。

"use-strict"
const functions = require('firebase-functions');
const admin = require("firebase-admin");
admin.initializeApp();

var notificationDB;
var followedUserRef;
var followingUserRef;
var followingText;
var followingImageProfile;
var followedDToken_id;
var following;
var followingFullname;
exports.sendNotification =functions.database.ref("Notifications/{followed}/{notification_id}").onWrite((snapshot,context)=>{
    const followed = context.params.followed;
    const notification_id = context.params.notification_id;

    notificationDB = admin.database().ref(`Notifications/${followed}/${notification_id}`);
    console.log("Notification DB : "+notificationDB);
    notificationDB.on("value",(snapshotOne)=>{
        following = snapshotOne.val().userid;      
        followingText = snapshotOne.val().text;
    });

    followedUserRef = admin.database().ref(`Users/${followed}`);
    followedUserRef.on("value",(snapshot)=>{
        if(snapshot.val().token_id===null){
            followedDToken_id = "null";
        }else
        followedDToken_id = snapshot.val().token_id;   
    });

    followingUserRef = admin.database().ref(`Users/${following}`);
    followingUserRef.on("value",(snapshot)=>{
        followingFullname = snapshot.val().fullname;   
        followingImageProfile = snapshot.val().imageurl;   
    });

    console.log("Following: "+following);
    console.log("Followed: "+followed);
    console.log("followed user Ref: "+followedUserRef)
    console.log("NAME: "+followingFullname);
    console.log("FOLLOWING TEXT: "+followingText);
    console.log("tokken: "+followedDToken_id);
    console.log("IMAGE: "+followingImageProfile);
});

预期的结果应该在第一次尝试时显示，但第一次失败并在第二次获取值。

Answer 1

您的代码并没有像您预期的那样完全按顺序执行，有请求发送到服务器，您需要在回调中记录控制台日志。例如这里

notificationDB = admin.database().ref(`Notifications/${followed}/${notification_id}`);
console.log("Notification DB : "+notificationDB);
notificationDB.on("value",(snapshotOne)=>{
    following = snapshotOne.val().userid;      
    followingText = snapshotOne.val().text;
});

following 只会在响应时初始化，这将在您控制台日志后执行。因此，您需要根据以下原则重构代码：

• 你初始化你的变量
• 然后调用发送请求的函数
• 在回调中执行控制台日志

使用 Promise API 会更优雅。