Swift 3.0中的完成处理程序

Question

我使用下面的代码与我的服务器同步数据.完成任务后,我想打电话给:

self.refreshControl?.endRefreshing()

但是,我想确保它发生在此方法中可能发生的任何事情之后.这是我要使用完成处理程序的地方吗？这让我感到困惑,因为我已经运行了在获得http响应后执行的代码.如果我添加一个完成处理程序,它会在收到http响应后执行吗？我可以将我的endRefreshing()代码放在那里,这可能发生在下面的代码中可能发生的任何事情之后吗？谢谢!

func syncCustomers(token: String) {
    let url:NSURL = NSURL(string: Constants.Api.BaseUrl + "api/customer")!
    let session = URLSession.shared
    let request = NSMutableURLRequest(url: url as URL)
    request.setValue("Bearer \(token)", forHTTPHeaderField: "Authorization")
    request.httpMethod = "GET"
    let task = session.dataTask(with: request as URLRequest) { (data, response, error) in
        guard let data = data else { return }
        do {
            if error != nil {
                self.showAlert(title: "Error", message: error!.localizedDescription)
            }
            else if let httpResponse = response as? HTTPURLResponse {
                if httpResponse.statusCode == 200 {
                    let json = try JSONSerialization.jsonObject(with: data, options: .allowFragments) as? Array<Any>
                    DispatchQueue.global().async {
                        for item in json! {
                            if let customer = Customer(json: item as! [String : Any]) {
                                _ = SqliteDB.instance.replaceCustomer(customer: customer)
                            }
                        }
                        self.customers = SqliteDB.instance.getCustomers()
                        self.tableView.reloadData()
                    }
                } else if httpResponse.statusCode == 401 {
                    self.showAlert(title: "Error", message: "Unauthorized. Please try logging in again.")

                }
            }
        } catch let error as NSError {
            self.showAlert(title: "Error", message: error.localizedDescription)
        }
    }
    task.resume()
}

Answer 1

完成或关闭只是一个包含在参数中的函数......

你可以创建一个像这样的闭包函数...

func doSomethingAsync(completion: () -> ()) {
}

参数completion的类型() -> ()是......它是一个->不带输入参数()并返回void 的函数().

你也可以做一个像...这样的功能

// (inputs) -> (outputs)
(String) -> ()

或者您想要的任何输入或输出.

现在,就像你在问题中一样.这个函数可以调用其他一些异步函数...

func myAsyncFunction(completion: () -> ()) {

    someOtherAsyncFunction() {

        // This is the completion of "someOtherAsyncFunction"

        // Call YOUR completion here...
        completion()
    }

}

为了确保在完成其他异步方法之后调用完成,请将其置于另一个方法的完成之内.像上面一样.

现在,打电话给你,你可以做...

self.myAsyncFunction() {
    // your completion block code here.
}

现在,在其他异步方法完成后,将调用完成块代码.

当然,如果你在另一个完成中有多个路径(比如错误等等),那么你必须在每个端点调用你的完成...

func myAsyncFunction(completion: () -> ()) {

    someOtherAsyncFunctionWithAPossibleError() {
        error in

        if error != nil {
            completion()
            // this return means the other completion won't be run
            return
        }

        completion()
    }

}

Answer 2

斯威夫特4:

1. 创建一个完成块.

   func getDataFromJson(url: String, parameter: String, completion: @escaping (_ success: [String : AnyObject]) -> Void) {
   
       //@escaping...If a closure is passed as an argument to a function and it is invoked after the function returns, the closure is @escaping.
   
       var request = URLRequest(url: URL(string: url)!)
       request.httpMethod = "POST"
       let postString = parameter
   
       request.httpBody = postString.data(using: .utf8)
       let task = URLSession.shared.dataTask(with: request) { Data, response, error in
   
           guard let data = Data, error == nil else {  // check for fundamental networking error
   
               print("error=\(error)")
               return
           }
   
           if let httpStatus = response as? HTTPURLResponse, httpStatus.statusCode != 200 {  // check for http errors
   
               print("statusCode should be 200, but is \(httpStatus.statusCode)")
               print(response!)
               return
   
           }
   
           let responseString  = try! JSONSerialization.jsonObject(with: data, options: .allowFragments) as! [String : AnyObject]
           completion(responseString)
   
   
   
       }
       task.resume()
   }
   

2. 通话方式

   getDataFromJson(url: "http://example.com", parameter: "vehicle_type=Car", completion: { response in
           print(response)
   
       })