Swift - 按钮（UIButton）的用法

import UIKitclass ViewController: UIViewController {    override func viewDidLoad() {        super.viewDidLoad()        // 创建一个ContactAdd类型的按钮        let button = UIButton(type: .ContactAdd)        button.frame = CGRectMake(10, 150, 100, 30)        button.setTitle("按钮", forState: UIControlState.Normal)        self.view.addSubview(button)        // 对于 Custom定制类型按钮，代码可以简化为        let btn = UIButton(frame: CGRectMake(10,200,100,30))        self.view.addSubview(btn)        // 按钮文字设置        btn.setTitle("普通", forState: UIControlState.Normal)        btn.setTitle("触摸", forState: UIControlState.Highlighted)        btn.setTitle("禁用", forState: UIControlState.Disabled)        // 按钮文字颜色设置        btn.setTitleColor(UIColor.whiteColor(), forState: UIControlState.Normal)        // 按钮文字阴影颜色设置        btn.setTitleShadowColor(UIColor.grayColor(), forState: UIControlState.Normal)        // 按钮背景颜色        btn.backgroundColor = UIColor.blueColor()        // 按钮文字图标的设置        btn.setImage(UIImage(named: "icon1"), forState: UIControlState.Normal)        btn.adjustsImageWhenHighlighted = false // 触摸按钮也不会变暗        btn.adjustsImageWhenDisabled = false // 禁用下按钮也不会变暗        // 设置按钮背景图片        btn.setBackgroundImage(UIImage(named: "background1"), forState: UIControlState.Normal)        // 按钮触摸事件响应        btn.addTarget(self, action: #selector(tapped(_:)), forControlEvents: UIControlEvents.TouchUpInside)    }    /**     按钮触摸事件方法     */    func tapped(button:UIButton){        print(button.titleForState(UIControlState.Normal))    }}