popToViewController、pushViewController问题

想实现这样一个效果： VC6 -->VC7  -->在VC7的点击事件里回到VC6，在push到VC8

UINavigationController *navVC = self.navigationController;
for (UIViewController *temp in self.navigationController.viewControllers) {
if ([temp isKindOfClass:[ViewController6 class]]) {
[self.navigationController popToViewController:temp animated:NO];
break;
}
}

ViewController8 *vc8 = [[ViewController8 alloc]init];
/*
ViewController6 *vc6 = [[ViewController6 alloc]init];
UINavigationController *_navController = [[UINavigationController alloc]initWithRootViewController:vc6];
NSLog(@"-new-nav:%@",_navController);
UIViewController *currViewController = (UIViewController *)_navController.topViewController;
[currViewController.navigationController pushViewController:vc8 animated:NO];
*/
[navVC pushViewController:vc8 animated:YES];

上面代码注释的部分是我当时犯的错误。会push不到VC8
看下面的图就可以很清楚 的理解了，地址发生改变。