ios - 如何使闭包作为函数参数可选

Question

我有一个助手来显示 AlertView:

func showAlertBoxOK(headline:String, message:String, OkButtonText:String, viewController:UIViewController, completionOK:() -> Void){

    let alertController = UIAlertController(title: headline, message: message, preferredStyle:UIAlertControllerStyle.Alert)

    alertController.addAction(UIAlertAction(title: OkButtonText, style: UIAlertActionStyle.Default)
        { action -> Void in
            if completionOK() != nil {
                completionOK()
            }
        })
    viewController.presentViewController(alertController, animated: true, completion: nil)
}

现在我想让参数completionOK可选。我试过了完成OK:() -> 无效？ = nil` 但他给了我一个编译器错误。我的调用应该像这样不带参数:

showAlertBoxOK("Could not retrieve position", "Edit iOS Settings - GeoLocation denied. Sorry. Please fix that und restart App.", "OK", self)

参数如下:

showAlertBoxOK("Could not retrieve position", "Edit iOS Settings - GeoLocation denied. Sorry. Please fix that und restart App.", "OK", self, { println("hello world") })

有什么帮助吗？

Answer 1

您可以使用不同的方法并使用默认值定义参数，如下所示:

func showAlertBoxOK(headline:String, message:String, OkButtonText:String, viewController:UIViewController, completionOK:() -> Void = {}){

    let alertController = UIAlertController(title: headline, message: message, preferredStyle:UIAlertControllerStyle.Alert)

    alertController.addAction(UIAlertAction(title: OkButtonText, style: UIAlertActionStyle.Default)
        { action -> Void in
            completionOK()
        })
    viewController.presentViewController(alertController, animated: true, completion: nil)
}

这样就可以用两种不同的方式调用函数，同时也简化了函数的定义。