如何让UIViewController透明

在显示该UIViewController之前,修改两个属性

1. 设置背景颜色为 UIColor.clearColor()
2. 设置modalPresentationStyle 为 OverCurrentContext

eg:

let myVC = MyViewController()
myVC.view.backgroundColor = UIColor.clearColor()
myVC.modalPresentationStyle = UIModalPresentationStyle.OverCurrentContext