Swift：如何从completionHandler中获得价值

func getMac(_ session: String, _ kitcode: String) -> String { var mac: String = "" api.get_kit(session,kitcode) { resDevice in var m: String = "" for obj in resDevice { if obj.type == 1 { m = obj.mac break } } print("M : " + m) mac = m } return mac } 

我需要var m返回func

请帮帮我。

我想多解释一下，但是我不擅长语言。

Answer 1

你有两个select

1）通过closures作为你的函数参数

 func getMac(_ session: String, _ kitcode: String, completion: @escaping (String) -> Void) { api.get_kit(session,kitcode) { resDevice in var mac: String = "" for obj in resDevice { if obj.type == 1 { mac = obj.mac break } } print("M : " + mac) completion(mac) } } 

用法：

 getMac("session", "kitcode") { mac in print(mac) } 

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2）同步

2.1）一般

 let semaphore = DispatchSemaphore(value: 0) var text = "Some text" DispatchQueue.global(qos: .default).async { sleep(5) text = "Some other text" semaphore.signal() } print(text) // "Some text\n" _ = semaphore.wait(timeout: DispatchTime.distantFuture) print(text) // "Some other text\n" 

2.2）Alamofire

 let semaphore = DispatchSemaphore(value: 0) let request = Alamofire.request("https://someAlamofireRequest.url/") var text = "Some text" request.response(queue: DispatchQueue.global(qos: .default)) { _ in text = "Some other text" semaphore.signal() } print(text) // "Some text\n" _ = semaphore.wait(timeout: DispatchTime.distantFuture) print(text) // "Some other text\n" 

Answer 2

你必须使用块来获得价值

  func getMac(_ session: String, _ kitcode: String, successHandler: @escaping (_ success:String) -> Void) { var mac: String = "" api.get_kit(session,kitcode) { resDevice in var m: String = "" for obj in resDevice { if obj.type == 1 { m = obj.mac break } } print("M : " + m) mac = m successHandler(mac) } } 

Answer 3

  func getMac(_ session: String, _ kitcode: String, completion:(_ value: String) -> Void) { api.get_kit(session,kitcode) { resDevice in var mac: String = "" for obj in resDevice { if obj.type == 1 { mac = obj.mac break } } print("M : " + mac) completion(mac) } 

用作这个function

  getMac("yourstring", "yourstring", completion: { (value) -> () in print(value) })