ios development UITabbarController navigation issues

I customized a UITabbarController, is to inherit UITabbarController class BottomFrame, I AppDelegate inside
BottomFrame * mytabbarController = [[BottomFrame alloc] init];
UINavigationController * navController = [[UINavigationController alloc] initWithRootViewController: mytabbarController];
self.window.rootViewController = navController;
After the jump can be displayed properly navigation bar, but I want to change the navigation bar buttons found admission to the navigation bar is null, I NSLog (self.self.navigationController); printed is null, solve ah! Online, find great God help!
Reply:
Are generally controlled by the sub-navigation bar controller controller.
Reply:
tabbar controller array which put the navigation controller on the line
Reply:
BottomFrame * mytabbarController = [[BottomFrame alloc] init];
UINavigationController * navController = [[UINavigationController alloc] init];
NSArray * viewControllers = [NSArray arrayWithObjects: navController, nil];
[MytabbarController setViewController: viewControllers];
self.window.rootViewController = mytabbarController;