Swift 3.0中的完成处理程序

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()
    }

}

斯威夫特4:

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()
}

通话方式

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

    })