UIAlertController和UIAlertAction

    @IBAction func showAlert() {
        
        let alert = UIAlertController(title: "Hello World!", message: "This is my first app", preferredStyle: .Alert)
        
        //1.默认按钮
        let defaults = UIAlertAction(title: "Default", style: .Default, handler: nil)
        alert.addAction(defaults)

        //2.取消按钮
        let cancel = UIAlertAction(title: "Cancel", style: .Cancel, handler: nil)
        alert.addAction(cancel)
        
        //3.红色警告按钮
        let destructive = UIAlertAction(title: "Destructive", style: .Destructive, handler: nil)
        alert.addAction(destructive)
        
        presentViewController(alert, animated: true, completion: nil)
    }

运行结果：

 

发现：UIAlertAction.Cancel 始终显示在最后一个。