我的完成处理程序总是返回一个空数组，为什么？

Question

我有以下函数，该函数从Firebase提取数据，填充compliments数组，并假设通过完成handler将数组传递回来。

即使将对象添加到数组中，返回的数组始终为空？

我是否已将完成处理程序代码放置在错误的位置，我尝试在所有花括号中插入并且没有任何效果。

执行行handler(compliments, true)上的断点将输出以下内容：

0x0000000102bb3fe8 vipeeps`partial apply forwarder for closure #1 (Swift.Array<Any>, Swift.Bool) -> () in vipeeps.ConversationsListVC.loadNewInvitesData() -> () at ConversationsListVC.swift

功能：

    func getComplimentsReceived(forUserId forId: String, handler: @escaping (_ complimentPack: [[String : Any]] ,_ success: Bool) -> ()){

    var compliments = [[String : Any]]()//empty array to hold compliments

    REF_USERS_COMPLIMENTS.child(forId).observe(.value) { (snapshot) in


       for item in snapshot.children{


        let itemSnap = item as! DataSnapshot


        let dict = itemSnap.value as! [String : Bool]


        for (key, status) in dict {

            switch status {

            case true:
                //print(status)

                self.REF_USERS.child(snapshot.key).observeSingleEvent(of: .value, with: { (snapshot) in

                    let uid = snapshot.key
                    let name = snapshot.childSnapshot(forPath: "name").value as! String
                    let email = snapshot.childSnapshot(forPath: "email").value as! String
                    let profilePictureURL = snapshot.childSnapshot(forPath: "profilePictureURL").value as! String

                    let birthday = snapshot.childSnapshot(forPath: "birthday").value as! String
                    let firstName = snapshot.childSnapshot(forPath: "firstName").value as! String
                    let lastName = snapshot.childSnapshot(forPath: "lastName").value as! String
                    let gender = snapshot.childSnapshot(forPath: "gender").value as! String
                    let discoverable = snapshot.childSnapshot(forPath: "discoverable").value as! Bool
                    let online = snapshot.childSnapshot(forPath: "online").value as! Bool

                    let discoveryPrefs = snapshot.childSnapshot(forPath: "discoveryPrefs").value as! [String : Any]

                    let dictionary: [String : Any] = ["uid": uid, "name": name, "email": email, "profilePictureURL": profilePictureURL, "birthday": birthday, "firstName": firstName, "lastName": lastName, "gender": gender, "discoverable": discoverable, "online": online, "discoveryPrefs": discoveryPrefs]

                    let user = User(uid: uid, dictionary: dictionary)

                    let complimentPack = [
                        "type": "compliment",
                        "complimentId": key,
                        "active": status,
                        "fromUser": user
                        ] as [String : Any]

                    compliments.append(complimentPack)

                    print("compliments.count: \(compliments.count)")


                })//end observer

            case false:
                print(status)

                break

            }//end switch

         }//end for dict

       }//end for snapshot.item

      handler(compliments, true)

    }//end observe

 }//end func

数据结构：

Answer 1

您可能想使用调度组，所有异步observeSingelEvent调用完成后，调度组将被通知：

• 在您的observe代码中，创建一个新的DispatchGroup
• 在调用异步observeSingleEvent之前，请先enter组。
• 在asyc关闭结束时，您leave将该组
• 一旦所有enters和leave调用都匹配，就会调用notify，然后调用handler

查看此处：

func getComplimentsReceived(forUserId forId: String, handler: @escaping (_ complimentPack: [Any] ,_ success: Bool) -> ()){
    REF_USERS_COMPLIMENTS.child(forId).observe(.value) { (snapshot) in
        var compliments = [Any]()//empty array to hold compliments
        let dispatchGroup = DispatchGroup()
        for item in snapshot.children {

            for (key, status) in dict {

                switch status {
                    case true:
                        dispatchGroup.enter()
                        self.REF_USERS.child(snapshot.key).observeSingleEvent(of: .value, with: { (snapshot) in
                            // ...
                            compliments.append(complimentPack)
                            dispatchGroup.leave()
                    })//end observer
                    case false:
                        print(status)
                        break

                }//end switch

            }//end for dict

        } //end for snapshot.item

        dispatchGroup.notify(queue: .main) {
            handler(compliments, true)
        }
    } //end observe

}//end func

添加编辑功能（通过@Roggie）：

func loadNewInvitesData(){


    guard let uid = Auth.auth().currentUser?.uid else { return }

    DataService.run.getInvitesAndCompliments(forUserId: uid) { (array, sucess) in


            for item in array {
                let user = item ["fromUser"] as! User
                let uid = user.uid
                print("user id: \(uid)")
                DataService.run.observeUser(forUserId: uid, handler: { (user) in
                    self.users.append(user)
                })
            }
        self.invites = array
        self.collectionView.reloadData()

    }

}//end func