Swift 2:从闭包中抛出 [英] Swift 2: Throw from closure

问题描述

我正在使用带有 try-catch 的错误处理将我的代码升级到 Swift 2.我一直在使用闭包 (NSURLSession)，我不能把它扔进去.

I'm upgrading my code to Swift 2 using error handling with try-catch. I've stuck with closure (NSURLSession), I can't throw inside it.

通常我使用这样的代码:

Generally I'm using such code:

let request = NSURLRequest()

let task = NSURLSession.sharedSession().dataTaskWithRequest(request) {
    data, response, error in
    if error != nil {
        throw(ErrorType) // here some errortype enum
    }
}

但我收到错误消息:无法使用类型为……的参数列表调用 dataTaskWithRequest".我怎样才能从闭包中抛出?

But I'm receiving the error: "Cannot invoke dataTaskWithRequest with an argument list of type …". How can I throw from closure?

推荐答案

你不能在闭包内部抛出，因为闭包可以在稍后调用，当函数已经执行时.

You can't throw inside a closure because the closure can be called later, when the function is already executed.

在您的示例中，在 URLRequest 得到响应后异步调用闭包，此时调用函数已经执行.

In your example the closure is called asynchronously after the URLRequest got a response, at this time the calling function is already executed.

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