//获取当前屏幕显示的ViewController

• (UIViewController *)getCurrentVC
  {
  UIViewController *result = nil;
  //找到当前显示的View
  UIWindow * window = [[UIApplication sharedApplication] keyWindow];
  if (window.windowLevel != UIWindowLevelNormal)
  {
  NSArray *windows = [[UIApplication sharedApplication] windows];
  for(UIWindow * tmpWin in windows)
  {
  if (tmpWin.windowLevel == UIWindowLevelNormal)
  {
  window = tmpWin;
  break;
  }
  }
  }
  //获取View的ViewController
  UIView *frontView = [[window subviews] objectAtIndex:0];
  id nextResponder = [frontView nextResponder];

  if ([nextResponder isKindOfClass:[UIViewController class]])
  result = nextResponder;
  else
  result = window.rootViewController;

  return result;
  }

我们在非视图类中想要随时展示一个view时，需要将被展示的view加到当前view的子视图，或用当前view presentViewController，或pushViewContrller，这些操作都需要获取当前正在显示的ViewController。