ios - 在闭包外快速访问数据

Question

我是 iOS 新手。我有疑问，我们如何访问闭包内的数据或变量。以下是我的代码片段。

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

            }
        }
    }      

我想把 myResponseStr 放到外面，比如 self.myString=myResponseStr

Answer 1

您应该在调用 fetchData 的函数中使用完成处理程序闭包，例如:

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)
            }
        }
    }      
}

你可以这样调用它:

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