闭包外快速访问数据

问题描述

我是iOS的新手.我有一个疑问，我们如何才能在闭包内部访问数据或变量.以下是我的代码段.

I am newbie to iOS. I have query that how can we access data or variables inside closure. Following is my code snippet.

self.fetchData() { data in
       dispatch_async(dispatch_get_main_queue()) {
            println("Finished request")
            if let data = data { // unwrap your data (!= nil)
            let myResponseStr = NSString(data: data, encoding: NSUTF8StringEncoding) as! String

            }
        }
    }      

我想将myResponseStr带到外面，例如 self.myString = myResponseStr

I want to get myResponseStr outside, like self.myString=myResponseStr

推荐答案

您应在调用fetchData的函数中使用完成处理程序闭包，例如:

You should employ completion handler closure in the function that calls fetchData, e.g.:

func fetchString(completionHandler: (String?) -> ()) {
    self.fetchData() { responseData in
        dispatch_async(dispatch_get_main_queue()) {
            println("Finished request")
            if let data = responseData { // unwrap your data (!= nil)
                let responseString = NSString(data: data, encoding: NSUTF8StringEncoding) as? String
                completionHandler(responseString)
            } else {
                completionHandler(nil)
            }
        }
    }      
}

您会这样称呼它:

fetchString() { responseString in
    // use `responseString` here, e.g. update UI and or model here

    self.myString = responseString
}

// but not here, because the above runs asynchronously

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