有人能告诉我为什么它显示数组是空的吗

Question

我想向多个设备发送通知，为此，我通过查询文档获取令牌并将令牌保存到数组中，但这表明数组是空的。最可能的错误是因为我无法在数组中添加元素。

我的代码是：-

var registrationTokens=[];
const indexOfSender=usersList.indexOf(chatItem.senderUsername);
let removedUsername=usersList.splice(indexOfSender,1);      //to remove the senders name from list
usersList.forEach(async(element)=>{
const query = admin.firestore().collection('users').where("username","==",element);
const querySnapshot = await query.get();
if (querySnapshot.docs.length > 0) {
const doc = querySnapshot.docs[0];
const data = doc.data();
registrationTokens.push(data.androidNotificationToken); //adding token over here
}
else {
console.log("Unable to get token for the username ", element);
}
});


const message =
{
notification: {
title:'Message',
body: body,
imageUrl: url,
},
tokens: registrationTokens,
data: { recipient: senderUserId },
};
admin.messaging().sendMulticast(message)
.then(response =>
{
if (response.failureCount > 0) {
const failedTokens = [];
response.responses.forEach((resp, idx) => {
if (!resp.success) {
failedTokens.push(registrationTokens[idx]);
}
});
console.log('List of tokens that caused failures: ' + failedTokens);
}
else
{
console.log('Successfully sent messages ', response);
}
});

错误

Error: tokens must be a non-empty array
at FirebaseMessagingError.FirebaseError [as constructor] (/workspace/node_modules/firebase-admin/lib/utils/error.js:42:28)
at FirebaseMessagingError.PrefixedFirebaseError [as constructor] (/workspace/node_modules/firebase-admin/lib/utils/error.js:88:28)
at new FirebaseMessagingError (/workspace/node_modules/firebase-admin/lib/utils/error.js:254:16)
at Messaging.sendMulticast (/workspace/node_modules/firebase-admin/lib/messaging/messaging.js:294:19)
at sendNotificationForGroupChat (/workspace/index.js:238:35)
at exports.onCreateMessage.functions.region.firestore.document.onCreate (/workspace/index.js:116:9)
at process._tickCallback (internal/process/next_tick.js:68:7) 

Answer 1

forEach内部的async无法按预期工作。如果您添加一些日志记录，您将看到循环在其任何异步工作完成之前结束，在将令牌数组传递给FCM之前将其留空。循环中的每一次迭代都只是生成一个未解析的promise。您需要重写代码，以便在调用FCM之前真正等待所有这些承诺。

阅读更多信息：

• 使用带有forEach循环的async/await

Answer 2

对于循环，异步调用可以很好地工作：(

干杯