UIViewController推出的半透明效果

1.在ios7以前：

UIViewController *VC = [[UIViewController alloc]init];

self.modalPresentationStyle = UIModalPresentationCurrentContext;//关键

[self presentViewController:VC animated:YES completion:nil];

2.iOS8以后的方法：使用UIModalPresentationOverCurrentContext

UIViewController *VC = [[UIViewController alloc]init];
    VC.modalPresentationStyle = UIModalPresentationOverCurrentContext;//关键
    //UIModalPresentationOverFullScreen全屏效果
    [self presentViewController:VC animated:YES completion:nil];

3.可使用该方式判断系统版本

CGFloat versin = [[UIDevice currentDevice].systemVersion floatValue];