Swift study notes 1 hello world

I have been studying PHP for more than a year now, and I have accumulated a lot of notes, which are quite complicated. Let me write an article to sort them out.

Learning any language starts from hello world, hahaha

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//这个好像就是类似于OC的懒加载 （个人观点--菜鸡观点）
    fileprivate var helloBtn: UIButton = {

        let  helloBtn = UIButton(type:.custom)   //初始化UIButton 
        helloBtn.frame = CGRect(x: 100, y: 100, width: 205, height: 50) //设置frame
        helloBtn.backgroundColor = UIColor.blue     //设置背景颜色
        helloBtn.setTitle("欢迎", for: UIControlState.normal) //设置title （普通状态下）
        helloBtn.setTitleColor(UIColor.white, for: .normal)  //设置title的颜色 （普通状态下）
        helloBtn.setTitle("hello world", for: UIControlState.selected) //设置title （点击状态下）
        helloBtn.addTarget(self, action: #selector(helloBtnClick), for: .touchUpInside)  //添加点击事件
        return helloBtn
    }()

As for what effect we need to achieve, let’s wait for the code Finished

After initializing a button OK, you need to load it on the View and display it

 //这个方法相当于 OC里的 -(void)viewDidLoad;
    override func viewDidLoad() {
        super.viewDidLoad()

        //在view上添加一个按钮
        self.view .addSubview(helloBtn)
    }

ok, but there is still a click event method

extension ViewController{
    

//这个就是点击事件出发的方法
    @objc fileprivate func helloBtnClick(sender :UIButton){
        
//改变状态
        sender.isSelected = !sender.isSelected;
        
    }
}

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