IOS 下获取 rootviewcontroller 的版本不同的问题解决办法

[[UIApplication sharedApplication].keyWindow.rootViewController presentModalViewController:self animated:NO];

// Set RootViewController to window
  if ( [[UIDevice currentDevice].systemVersion floatValue] < 6.0)
  {
    // warning: addSubView doesn't work on iOS6
    [window addSubview: viewController.view];
  }
  else
  {
    // use this method on ios6
    [window setRootViewController:viewController];
  }
 

if ( [[UIDevice currentDevice].systemVersion floatValue] < 6.0)
  {
    // warning: addSubView doesn't work on iOS6
    NSArray* array=[[UIApplication sharedApplication]windows];
    UIWindow* win=[array objectAtIndex:0];
    
    UIView* ui=[[win subviews] objectAtIndex:0];
    UIViewController* ctrol=(UIViewController*)[ui nextResponder];
  }
  else
  {
    // use this method on ios6
    UIViewController* ctrol=[UIApplication sharedApplication].keyWindow.rootViewController];
  }