了解快速的Alamofire完成处理程序 [英] Understanding swift Alamofire completionHandler

问题描述

我的API类中有以下两种方法可从API获取数据：

I have these two methods in my API class to get data from an API:

func authenticateUser(completionHandler: (responseObject: String?, error: NSError?) -> ()) {
        makeAuthenticateUserCall(completionHandler)
    }

    func makeAuthenticateUserCall(completionHandler: (responseObject: String?, error: NSError?) -> ()) {
        Alamofire.request(.GET, loginUrlString)
            .authenticate(user: "a", password: "b")
            .responseString { request, response, responseString, responseError in
                completionHandler(responseObject: responseString as String!, error: responseError)
        }
    }

然后在另一个类中，我使用以下代码访问数据：

Then in another class i use the following code to access the data:

API().authenticateUser{ (responseObject, error) in
    println(responseObject)
}

代码正在工作，但我不明白

The code is working but i don't understand it completely.

1. func authenticateUser具有参数completedler：（responseObject：String ?, error：NSError？）->（），是这是对completionHandler方法的引用吗？还是物体？ ->（）的目的是什么？


2. 当我调用authenticateUser函数时，我实际上如何访问响应？我的任何一个API函数都没有任何回报，..}语法中的funcname {（parameter，parameter）似乎真的很奇怪。

推荐答案

completionHandler 是闭包参数。正如Swift文档所说：

completionHandler is a closure parameter. As Swift documentation says:

闭包是自包含的功能块，可以在代码中传递和使用。 Swift中的闭包类似于C和Objective-C中的块以及其他编程语言中的lambda。

Closures are self-contained blocks of functionality that can be passed around and used in your code. Closures in Swift are similar to blocks in C and Objective-C and to lambdas in other programming languages.

所以，闭包是什么

在您的情况下，您调用 authenticateUser ，然后传递一个接受（responseObject，错误）并执行 println（responseObject）。 authenticateUser（）在 completionHandler 参数下收到您的关闭，然后调用 makeAuthenticateUserCall（）将您的 completionHandler 闭包传递给它。

In your case, you call authenticateUser and you pass a closure that receives (responseObject, error) and executes println(responseObject). authenticateUser() receives your closure under the completionHandler parameter and it then calls makeAuthenticateUserCall() passing your completionHandler closure to it.

然后再次查看定义，您可以看到 func makeAuthenticateUserCall（completionHandler：（responseObject：String ?, error：NSError？）-> （）），这意味着像 authenticateUser（） makeAuthenticateUserCall（）一样，以 completionHandler 的名称接收一个闭包作为参数。 makeAuthenticateUserCall（）使用 AlamoFire 发出网络请求，并再次捕获闭包下的响应，并将其作为 responseString（）方法。因此，您具有：

Then again, looking at the definition you can see func makeAuthenticateUserCall(completionHandler: (responseObject: String?, error: NSError?) -> ()) that means that like authenticateUser() makeAuthenticateUserCall() is a function that receives a closure as a parameter, under the name of completionHandler. makeAuthenticateUserCall() makes a network request using AlamoFire and you capture the response under a closure again that you pass as parameter of the responseString() method. So you have:

//here you call authenticateUser with a closure that prints responseObject
API().authenticateUser{ (responseObject, error) in
    println(responseObject)
}

然后：

//authenticateUser receives your closure as a parameter
func authenticateUser(completionHandler: (responseObject: String?, error: NSError?) -> ()) {
    //it passes your closure to makeAuthenticateUserCall
    makeAuthenticateUserCall(completionHandler)
}

//makeAuthenticateUserCall receives your closure
func makeAuthenticateUserCall(completionHandler: (responseObject: String?, 
error: NSError?) -> ()) {
    Alamofire.request(.GET, loginUrlString)
        .authenticate(user: "a", password: "b")
        //here you pass a new closure to the responseString method
        .responseString { request, response, responseString, responseError in
            //in this closure body you call your completionHandler closure with the 
            //parameters passed by responseString and your code gets executed 
            //(that in your case just prints the responseObject)
            completionHandler(responseObject: responseString as String!, error: responseError)
    }
}

有关更多信息，请阅读文档： Swift闭包

For more information read the documentation: Swift Closures

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