swift 一句话创建子视图背景不透明的方法

let backView = UIView.init(frame: CGRectMake(0, 0, SCREEN_WIDTH, SCREEN_HEIGHT))

backView.backgroundColor=UIColor.blackColor().colorWithAlphaComponent(0.3)

let numberView = UIView.init(frame: CGRectMake(20, 250, SCREEN_WIDTH-40, 150))

numberView.backgroundColor=UIColor.whiteColor()

backView.addSubview(numberView)

return backView