self.navigationController is null after it is assign as RootViewController?

I created a new xcode project as View-based application, and I have a set of UIViewController(s) which I plan to use inside separate UINavigationController(s).

In ParentViewController.m before all the UINavigationController(s) and after all myViewControllers been initiated:

NSMutableArray *navControllers = [[NSMutableArray array];开发者_JAVA技巧
for (id aVC in self.myViewControllers) {
    UINavigationController *navController = [[UINavigationController alloc] initWithRootViewController:aVC];

    //[aVC setNavigationController:navController];
    [navController setNavigationBarHidden:YES];
    [navController setToolbarHidden:YES];
    [navControllers addObject:navController];
    [navController release];
}

_navigationControllers = [[NSArray arrayWithArray:navigationControllers] retain];

_navigationControllers is retained as a member of ParentViewController, so I suppose all my navigation controllers initiated inside for-loop are kept by _navigationControllers so they won't be released or become nil, but when I try to use navigationController in MyViewController to push SomeOtherViewController, it doesn't work:

- (IBAction)pushDetailView {
     [self.navigationController pushViewController:self.detailViewController animated:YES];
}

I put a breakpoint before pushViewController:someOtherViewController, and "po [self navigationController]", the console tells me it is a nil reference.

I assumed that when I do [[UINavigationController alloc] initWithRootViewController:aVC], the underlying mechanism would assign the navigationController as aVC.navigationController, because the Apple "View Controller Programming Guide for iOS" does the same without assigning navigationController to rootController.

Unless I unmark the second line of the for-loop //[aVC setNavigationController:navController];, the navigationController does not exist in aVC.

Am I misunderstanding the mechanism? Is there another solution for my case? Thanks in advance!

_navigationControllers = [NSMutableArray array];
for (id aVC in self.myViewControllers) {
    UINavigationController *navController = [[UINavigationController alloc] initWithRootViewController:aVC];

    //[aVC setNavigationController:navController];
    [navController setNavigationBarHidden:YES];
    [navController setToolbarHidden:YES];
    [navControllers addObject:navController];
}

// assuming index 0 navigation controller is with 'ParentViewController'
self.rootViewController = [_navigationControllers objectAtIndex:0];

check with this.