先上个图

我们先打开Xcode工程，File->New->Playground或者option+shift+command+N

选择Single View。

然后就能看到熟悉的swift的控制器的相关代码了。

import UIKit
import PlaygroundSupport

class MyViewController : UIViewController {
    
    override func viewDidLoad() {
        super.viewDidLoad()
        self.view.backgroundColor = UIColor.white
        
        let label = UILabel()
        label.frame = CGRect(x: 100, y: 200, width: 200, height: 20)
        label.text = "Hello World!"
        label.textColor = .black
        label.textAlignment = .center
        label.backgroundColor = UIColor.cyan
        
        self.view.addSubview(label)
        
        let animate = CABasicAnimation(keyPath: "opacity")
        animate.fromValue = 0
        animate.toValue = 0.8
        animate.duration = 0.75
        animate.repeatCount = MAXFLOAT
        animate.timingFunction = CAMediaTimingFunction(name: kCAMediaTimingFunctionEaseInEaseOut)
        animate.fillMode = kCAFillModeBoth
        animate.autoreverses = true
        
        label.layer.add(animate, forKey: "key_opacity")
    }
}
// Present the view controller in the Live View window
PlaygroundPage.current.liveView = MyViewController()


//let demoView = UIView(frame: CGRect(x: 0, y: 0, width: 100, height: 100))
//demoView.backgroundColor = UIColor.brown
//PlaygroundPage.current.liveView = demoView

通过PlaygroundSupport的PlaygroundPage.current.liveView就可以设置当前要显示的View或Controller了。效果如下。

1. 我们要如何看到界面呢？

打开assistant editor即可

2. 我们怎样调试界面呢？

按住左下角的三角按钮，会弹出一个菜单，选择Manually Run就可以手动运行Playground了，以后每次点击三角按钮才会运行Playground。

这是不是很简单呢？