谁能告诉我为什么显示数组为空？

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，但它显示该数组为空。最有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

async inside forEach 没有按照您预期的方式工作。如果添加一些日志记录，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。循环中的每次迭代只会生成一个未解决的承诺。在调用 FCM 之前，您需要重写代码以实际等待所有这些承诺。

了解更多相关信息：

Answer 2

for-of 循环可以很好地处理异步调用:)

干杯

谁能告诉我为什么显示数组为空？

Can anyone tell me why it is showing array is empty?

javascript

node.js

google-cloud-functions

firebase-cloud-messaging

google-cloud-firestore