swift - Dispatch Group 命令在代码中放在哪里？

Question

我试图在 for in 循环中运行一个函数 X 次，但是当所有函数都返回时，我想运行另一个函数。

目前我通过将最终功能延迟 1 秒来让它工作，但我真的想让 Dispatch Group 工作。

我已经通过各种在线示例和其他问题，但我尝试的似乎没有任何效果，我知道我目前拥有的代码不会工作，因为它每次运行 dispatchGroup.leave() 时 for in 函数发送而不是返回时。

我已经尝试将 DispatchGroup 代码放入函数中(位于另一个文件中)，但我被难住了，但我认为我已接近解决方案。

我还查看了信号量并使用计数并在每次循环运行时递增一个值，但我一直回到 DispatchGroups。

我最后的办法是问一个问题!

View Controller 代码

 @IBAction func removeDeviceBtn(_ sender: Any) {

    let dispatchGroup = DispatchGroup()

    for owner in arrOwnerList {
        dispatchGroup.enter()
        self.removeDevice(device: self.device, account: owner as! String, completion: self.completed)
        dispatchGroup.leave()
    }

    dispatchGroup.notify(queue: DispatchQueue.main, execute: {
        self.removeDeviceFromServer(device: self.device)
        self.sendEmail(to:"gordon@example.co.uk", subject:self.device+" has been removed", text:self.device+" has been removed from the server, please check the sim for bar and termination")
    })

其他文件中的函数代码作为扩展

  func completed(isSuccess: Bool) {
}

func removeDevice(device: String, account: String, completion: @escaping (Bool) -> Void) {

    let dictHeader : [String:String] = ["username":Username,"password":Password]
    let dictArray = [device]

    WebHelper.requestPUTAPIRemoveDevice(BaseURL+"rootaccount/removedevices/"+account+"?server=MUIR", header: dictHeader, dictArray: dictArray, controllerView: self, success: { (response) in
        if response.count == 0 {
            DispatchQueue.main.async {
                GlobalConstant.showAlertMessage(withOkButtonAndTitle: GlobalConstant.AppName, andMessage: Messages.ServerError, on: self)
            }
        }
        else {
            if response.count != 0 {
                let isSuccess = true
                completion(isSuccess)
            }
            else{
                DispatchQueue.main.async {
                    GlobalConstant.showAlertMessage(withOkButtonAndTitle: GlobalConstant.AppName, andMessage: Messages.NoDataFound, on: self)

                }
            }
        }
    }) { (error) in
        DispatchQueue.main.async {
            GlobalConstant.showAlertMessage(withOkButtonAndTitle: GlobalConstant.AppName, andMessage: error?.localizedDescription ?? Messages.ServerError, on: self)
        }
    }
}

WebHelper 文件中的代码

    class func requestPUTAPIRemoveDevice(_ strURL: String,header: Dictionary<String,String>,dictArray: Array<Any>, controllerView viewController: UIViewController, success: @escaping (_ response: [AnyHashable: Any]) -> Void, failure: @escaping (_ error: Error?) -> Void) {

    if GlobalConstant.isReachable() {
        DispatchQueue.main.async {
            LoadingIndicatorView.sharedInstance.showHUD()
        }
        let loginString = String(format: "%@:%@", header["username"]!, header["password"]!)
        let loginData: Data = loginString.data(using: String.Encoding.utf8)!
        let base64LoginString = loginData.base64EncodedString(options: NSData.Base64EncodingOptions())

        let headers = ["Authorization": "Basic "+base64LoginString, "Referer": "http://www.example.com"]

        let postData = try? JSONSerialization.data(withJSONObject: dictArray, options: [])

        let request = NSMutableURLRequest(url: NSURL(string: strURL)! as URL,
                                          cachePolicy: .useProtocolCachePolicy,
                                          timeoutInterval: 10.0)
        request.httpMethod = "PUT"
        request.allHTTPHeaderFields = headers
        request.httpBody = postData

        let session = URLSession.shared
        let dataTask = session.dataTask(with: request as URLRequest, completionHandler: { (data, response, error) -> Void in
            if (error != nil) {
                DispatchQueue.main.async {
                    LoadingIndicatorView.sharedInstance.hideHUD()
                }
                failure(error)
            } else {
                if let httpResponse = response as? HTTPURLResponse {
                    print("Server code \(httpResponse.statusCode)")
                    if httpResponse.statusCode == 200 || httpResponse.statusCode == 208 {
                        DispatchQueue.main.async {
                            LoadingIndicatorView.sharedInstance.hideHUD()
                        }
                        let jsonResult = try? JSONSerialization.jsonObject(with: data!, options:    JSONSerialization.ReadingOptions.mutableContainers)

                        if (jsonResult is NSDictionary) {
                            success(jsonResult as! [AnyHashable : Any])
                        }
                        else if (jsonResult is NSArray) {
                            success(["response":jsonResult as! NSArray])
                        }
                        else{
                          success(["response":httpResponse.statusCode])
                          DispatchQueue.main.async {
                        }

                        }
                    }
                    else{
                        DispatchQueue.main.async {
                            LoadingIndicatorView.sharedInstance.hideHUD()
                        }
                        failure(error)
                    }
                }
            }
        })

        dataTask.resume()
    }
    else {
        DispatchQueue.main.async {
            LoadingIndicatorView.sharedInstance.hideHUD()
            GlobalConstant.showAlertMessage(withOkButtonAndTitle: "", andMessage: "Internet not connected", on: viewController)
        }

    }
}

最终的解决方案(除了整理其他各种问题)是将 success(["response":httpResponse.statusCode]) 添加到 WebHelper 文件，更正了上面的代码

Answer 1

将 leave 放在完成处理程序中:

for owner in arrOwnerList {
    dispatchGroup.enter()
    removeDevice(device: device, account: owner as! String) { [weak self] success in
        self?.completed(isSuccess: success)
        dispatchGroup.leave()
    }
}

或者假设你在 completed 函数中没有真正做任何事情，我只是删除它:

for owner in arrOwnerList {
    dispatchGroup.enter()
    removeDevice(device: device, account: owner as! String) { _ in
        dispatchGroup.leave()
    }
}

---

我注意到您在 removeDevice 中有不调用完成处理程序的执行路径。确保每条执行路径都调用完成处理程序，否则您的调度组将永远无法解析。

func removeDevice(device: String, account: String, completion: @escaping (Bool) -> Void) {

    let dictHeader = ["username": Username, "password": Password]
    let dictArray = [device]

    WebHelper.requestPUTAPIRemoveDevice(BaseURL+"rootaccount/removedevices/"+account+"?server=MUIR", header: dictHeader, dictArray: dictArray, controllerView: self, success: { response in
        DispatchQueue.main.async {
            if response.count == 0 {
                GlobalConstant.showAlertMessage(withOkButtonAndTitle: GlobalConstant.AppName, andMessage: Messages.ServerError, on: self)
                completion(false)
            } else {
                completion(true)
            }
        }
    }, failure: { error in
        DispatchQueue.main.async {
            GlobalConstant.showAlertMessage(withOkButtonAndTitle: GlobalConstant.AppName, andMessage: error?.localizedDescription ?? Messages.ServerError, on: self)
            completion(false)
        }
    })
}

顺便说一句，我不知道“failure”闭包的名称，所以我假设它是failure，但根据您的requestPUTAPIRemoveDevice 方法进行调整.我们通常会避免 Swift 中的多重闭包模式，但如果你要这样做，我会避免尾随闭包语法。它使第二个闭包的功能意图更加明确。

或者，这一切都回避了为什么 requestPUTAPIRemoveDevice 会启动 UI 更新的问题。我可能会把它放在 View Controller 方法中。所以 requestPUTAPIRemoveDevice 应该只传回足够的信息，以便 removeDeviceBtn 例程知道要呈现什么错误。这种为每次失败显示单独的错误消息的想法可能也值得怀疑。 (例如，如果你失去了互联网连接并试图删除一打设备，你真的想显示一打单独的错误消息吗？)但这超出了这个问题的范围。