[__NSArrayI objectAtIndex：]：索引2超出边界[0 .. 1]

Question

我使用[self.navigationController.viewControllers objectAtIndex:2]。所以我需要在NSArray中设置我的viewcontroller。但我试过下面的方法，然后我得到错误。我知道我没有2的数组。那么，我如何在数组中设置viewcontroller并将其作为rootviewcontroller。

ARimageViewController *arimage = [[ARimageViewController alloc] init];
UINavigationController *nav = [[UINavigationController alloc] initWithRootViewController:arimage];

SampleViewController *sample = [[SampleViewController alloc] init];
UINavigationController *nav1 = [[UINavigationController alloc] initWithRootViewController:sample];

SettingsViewController *settings = [[SettingsViewController alloc] init];
UINavigationController *nav2 = [[UINavigationController alloc] initWithRootViewController:settings];

NSArray* controllers = [NSArray arrayWithObjects:nav,nav1,nav2, nil];

self.window.rootViewController = nav;        
self.window.rootViewController = nav1; 
self.window.rootViewController = nav2;

PushViewcontroller：

SettingViewcontroller：

SettingsViewController *set=[[SettingsViewController alloc]init];
[self.navigationController pushViewController:set animated:YES];

返回pushviewcontroller：

Class vcClass = NSClassFromString(self.appViewControllerClassName);
id vc = [[vcClass alloc]  initWithNibName:nil bundle:nil];
[self.navigationController pushViewController:vc animated:YES];