使用storyboard或xib方式
1：設置presentation為：Over Current Context
2：設置彈出的ViewController的view的background為 clear color
使用代碼方式
1：presention (原ViewController)
vc.modalPresentationStyle = UIModalPresentationOverCurrentContext
[self presentViewController:vc animated:YES completion:nil]
2:presenting (彈出的ViewController)
self.view.backgroundColor = [UIColor clearColor];
