代理在swift？

如何做一个委托，即NSUserNotificationCenterDelegate在swift？

它与obj-c没有什么不同。
首先，必须在类声明中指定协议，如下所示：

class MyClass: NSUserNotificationCenterDelegate

实现将如下所示：

// NSUserNotificationCenterDelegate implementation
func userNotificationCenter(center: NSUserNotificationCenter,didDeliverNotification notification: NSUserNotification) {
    //implementation
}

func userNotificationCenter(center: NSUserNotificationCenter,didActivateNotification notification: NSUserNotification) {
    //implementation
}

func userNotificationCenter(center: NSUserNotificationCenter,shouldPresentNotification notification: NSUserNotification) -> Bool {
    //implementation
    return true
}

当然，你必须设置委托。例如：

NSUserNotificationCenter.defaultUserNotificationCenter().delegate = self;