如何在Swift中显示来自另一个类的警报？

Question

我有一个主类,AddFriendsController它运行以下代码行:

ErrorReporting.showMessage("Error", msg: "Could not add student to storage.")

然后我有这个ErrorReporting.swift文件:

进口基金会

class ErrorReporting {
    func showMessage(title: String, msg: String) {
        let alert = UIAlertController(title: title, message: msg, preferredStyle: UIAlertControllerStyle.Alert)
        alert.addAction(UIAlertAction(title: "Ok", style: UIAlertActionStyle.Default, handler: nil))
        self.presentViewController(alert, animated: true, completion: nil)
    }
}

显然,self不会在这里工作,并给我一个错误.我如何引用当前打开的视图控制器(即AddFriendsController在这种情况下),因为我希望在许多不同的swift文件中使用相同的方法？

谢谢.

Answer 1

您可以为UIApplication创建扩展方法(例如),它将返回您的topViewController:

extension UIApplication {

    static func topViewController(base: UIViewController? = UIApplication.sharedApplication().delegate?.window??.rootViewController) -> UIViewController? {
        if let nav = base as? UINavigationController {
            return topViewController(nav.visibleViewController)
        }
        if let tab = base as? UITabBarController, selected = tab.selectedViewController {
            return topViewController(selected)
        }
        if let presented = base?.presentedViewController {
            return topViewController(presented)
        }

        return base
    }
}

然后你的课将如下所示:

class ErrorReporting {

    static func showMessage(title: String, msg: String) {
        let alert = UIAlertController(title: title, message: msg, preferredStyle: UIAlertControllerStyle.Alert)
        alert.addAction(UIAlertAction(title: "Ok", style: UIAlertActionStyle.Default, handler: nil))
        UIApplication.topViewController()?.presentViewController(alert, animated: true, completion: nil)
    }
}

方法需要static能够将其称为ErrorReporting.showMessage.

Answer 2

实际上,在我看来,视图控制器呈现操作应该在UIViewController实例上完成,而不是在模型类中完成.

一个简单的解决方法是将UIViewController实例作为参数传递

class ErrorReporting {
    func showMessage(title: String, msg: String, `on` controller: UIViewController) {
        let alert = UIAlertController(title: title, message: msg, preferredStyle: UIAlertControllerStyle.Alert)
        alert.addAction(UIAlertAction(title: "Ok", style: UIAlertActionStyle.Default, handler: nil))
        controller.presentViewController(alert, animated: true, completion: nil)
    }
}

并在下面调用它

ErrorReporting.showMessage("Error", msg: "Could not add student to storage.", on: self)

Answer 3

Swift 3版本的Maksym Musiienko的答案如下:

extension UIApplication {

    static func topViewController(base: UIViewController? = UIApplication.shared.delegate?.window??.rootViewController) -> UIViewController? {

        if let nav = base as? UINavigationController {
            return topViewController(base: nav.visibleViewController)
        }

        if let tab = base as? UITabBarController, let selected = tab.selectedViewController {
            return topViewController(base: selected)
        }

        if let presented = base?.presentedViewController {
            return topViewController(base: presented)
        }

        return base
    }
}