IOS(Swift)使用系统UIAlertView方法做吐司效果

　　 /**
     *显示弹出信息
     */
    class func showAlertMessage(_ str:String,showtime Num:Double){
        
        let alert = UIAlertView(title: str, message: nil, delegate: nil, cancelButtonTitle: nil);
        alert.show()
        //        self.performSelector(#selector(dismissAlert(_:)), withObject: alert, afterDelay: Num)
        let dispatchTime: DispatchTime = DispatchTime.now() + Double(Int64(0.10 * Num * Double(NSEC_PER_SEC))) / Double(NSEC_PER_SEC)
        DispatchQueue.main.asyncAfter(deadline: dispatchTime, execute: {
            dismissAlert(alert)
        })
    }
    
    class func dismissAlert(_ alert:UIAlertView){
        alert.dismiss(withClickedButtonIndex: alert.cancelButtonIndex, animated: true)
    }