返回完成块中方法的对象 [英] Return object for a method inside completion block

问题描述

我想创建一个带有URL参数的方法，该参数返回调用该URL的响应。
如何返回方法的完成块中获得的数据？

I want to make a method with URL parameter that returns the response of calling that URL. How can I return the data obtained inside a completion block for a method?

class func MakeGetRequest(urlString: String) -> (data: NSData, error: NSError)
{
    let url = NSURL(string: urlString)
    var dataResponse: NSData
    var err: NSError

    let task = NSURLSession.sharedSession().dataTaskWithURL(url!, completionHandler: { (data, response, error) -> Void in
           //How can I return the data obtained here....
    })

    task.resume()
}

推荐答案

如果您希望 MakeGetRequest 方法返回通过 dataTaskWithURL 你不能。该方法执行异步调用，这很可能在 MakeGetRequest 已经返回后完成 - 但是更一般地，它不能以确定性的方式知道。

If you want the MakeGetRequest method to return data obtained via dataTaskWithURL, you can't. That method performs an asynchronous call, which is most likely completed after the MakeGetRequest has already returned - but more generally it cannot be know in a deterministic way.

通常，异步操作通过闭包处理 - 而不是返回数据的方法，你向它传递一个闭包，接受在你的代码版本中返回的参数 - 完成 dataTaskWithURL ，您调用完成处理程序关闭，提供适当的参数：

Usually asynchronous operations are handled via closures - rather than your method returning the data, you pass a closure to it, accepting the parameters which are returned in your version of the code - from the closure invoked at completion of dataTaskWithURL, you call that completion handler closure, providing the proper parameters:

class func MakeGetRequest(urlString: String, completionHandler: (data: NSData, error: NSError) -> Void) -> Void
{
    let url = NSURL(string: urlString)
    var dataResponse: NSData
    var err: NSError

    let task = NSURLSession.sharedSession().dataTaskWithURL(url!, completionHandler: { (data, response, error) -> Void in
        completionHandler(data: data, error: error)
    })

    task.resume()
}

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