swift 纯代码创建view视图

import UIKit
//继承UIView
class demoView : UIView{
//获取屏幕尺寸
let main = UIScreen.main.bounds.size
//初始化
override init(frame: CGRect) {
        super.init(frame: frame)
        //设置背景为灰色
        self.backgroundColor = UIColor.gray
}
//自动布局
override func layoutSubviews() {
        //设置view的大小和位置
        self.frame = CGRect(x: 0, y: 0, width: main.width, height: main.height)
}
required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
}

一个简单的灰色背景的View就创建成功了!
然后在你的UIViewController里面加载demoView就可以了代码如下

import UIKit

class beginView: UIViewController {
    let demo = demoView()
    override func viewDidLoad() {
        super.viewDidLoad()
        view.addSubview(demo)
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
    }
}