在执行下一个操作之前等待请求完成

我想知道在执行另一段代码之前如何等待发送请求完成上传（并得到响应）的操作。 我试图用NSOperations做到这一点：

let testOp = BlockOperation { var result = 0 for i in 1...1000000000 { result += i } } let logOp = BlockOperation { self.debug.log(tag: "test", content: "testing") } logOp.completionBlock = { print("------- logOp completed") } logOp.addDependency(testOp) let sendOp = BlockOperation { self.debug.sendLog() //uploads log, using URLSession.shared.dataTask } sendOp.completionBlock = { print("------- sendOp completed") } sendOp.addDependency(logOp) let emptyOp = BlockOperation { self.debug.empty() } emptyOp.completionBlock = { print("------- emptyOp completed") } emptyOp.addDependency(sendOp) let queue = OperationQueue() queue.addOperations([testOp, logOp, sendOp, emptyOp], waitUntilFinished: false) 

输出：

 ------- logOp completed *** Sending debug log (coming from self.debug.sendLog()) ------- sendOp completed ------- emptyOp completed *** sendLog uploaded (coming from self.debug.sendLog()) 

基于我的代码我期望输出为：

 ------- logOp completed *** Sending debug log *** sendLog uploaded ------- sendOp completed ------- emptyOp completed 

我怎么做到这一点？ 我可以用NSOperations做到这一点吗？

有关debug.sendLog（）函数的其他详细信息：

 func sendLog() { ... var urlRequest = URLRequest(url: url!) urlRequest.httpMethod = "POST" ... let session = URLSession.shared let task = session.dataTask(with: urlRequest, completionHandler: { (data, response, error) in ... DispatchQueue.main.async { print("*** sendLog uploaded") } }) task.resume() } 

Answer 1

您可以将完成块直接添加到sendLog方法并sendLog所有块操作内容。

 func sendLog(withCompletion completion: (() -> Void)) { ... var urlRequest = URLRequest(url: url!) urlRequest.httpMethod = "POST" ... let session = URLSession.shared let task = session.dataTask(with: urlRequest, completionHandler: { (data, response, error) in ... completion?() }) task.resume() } 

然后像这样调用你的sendLog方法：

 sendLog(withCompletion: { // Execute the code you want to happen on completion here. })