#坑1# iOS8以后presendViewController透明效果无效

本文出自

http://mokai.github.io/2015/10/ios-bug-viewcontroller_translucent/

iOS弹出的视图背景默认是黑色，如果想去掉，以往我们使用 self.modalPresentationStyle = .CurrentContext 就可以实现效果，如以下半透明的代码

    let vc = UIViewController()
    vc.view.backgroundColor = UIColor(red:0.000 , green:0.000 , blue:0.000, alpha:0.5)
    self.modalPresentationStyle = .CurrentContext
    self.presentViewController(vc, animated: true, completion: nil)

但是你会发现这段代码在iOS8、iOS9上面运行依旧一片黑，因此iOS8以后得这么干

let vc = UIViewController()
vc.view.backgroundColor = UIColor(red:0.000 , green:0.000 , blue:0.000, alpha:0.5)
if let version = Float(UIDevice.currentDevice().systemVersion) where version >= 8{
    vc.modalPresentationStyle = .OverCurrentContext //注意此处是弹出VC对象，不是self
}else{
    self.modalPresentationStyle = .CurrentContext
}
self.presentViewController(vc, animated: true, completion: nil)

iOS8后增加了OverCurrentContext取代CurrentContext，并且设置的对象是弹出的VC