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];  }