ios - swift 3 :Closure use of non-escaping parameter may allow it to escape

Question

我有以下函数，其中有完成处理程序，但出现此错误:

Closure use of non-escaping parameter may allow it to escape

这是我的代码:

func makeRequestcompletion(completion:(_ response:Data, _ error:NSError)->Void)  {
    let urlString = URL(string: "http://someUrl.com")
    if let url = urlString {
        let task = URLSession.shared.dataTask(with: url, completionHandler: { (data, urlRequestResponse, error) in
            completion(data, error) // <-- here is I'm getting the error
        })
    task.resume()
    }
}

你们中有人知道我为什么会收到此错误吗？

非常感谢你的帮助

Answer 1

看起来您需要明确定义允许闭包转义。

来自Apple Developer docs ,

A closure is said to escape a function when the closure is passed as an argument to the function, but is called after the function returns. When you declare a function that takes a closure as one of its parameters, you can write @escaping before the parameter’s type to indicate that the closure is allowed to escape.

TLDR；在完成变量后添加@escaping关键字:

func makeRequestcompletion(completion: @escaping (_ response:Data, _ error:NSError)->Void)  {
    let urlString = URL(string: "http://someUrl.com")
    if let url = urlString {
        let task = URLSession.shared.dataTask(with: url, completionHandler: { (data, urlRequestResponse, error) in
            completion(data, error) // <-- here is I'm getting the error
        })
        task.resume()
    }
}