Swift 设置View的背景图片

//1.通过UIImageView设置
        self.view.insertSubview(UIImageView.init(image: UIImage.init(named: "123")),at: 0)
        
        //2.通过layer的content
       self.view.layer.contents = UIImage.init(named: "123")?.cgImage
       self.view.contentMode = UIViewContentMode.scaletoFill