pushViewController in viewWillAppear failed after popToRootViewController - ios

Question

there have 3 view controllers, A,B,C, all designed in storyboard.
in all pushViewController: controllers were got from [self.navigationController instantiateViewControllerWithIdentifier:#"A/B/C_Controller"];
In A_ViewController ( root controller ):
-(void)viewWillAppear
{
[self.navigationController pushViewController:B_Controller animated:YES];
}
In B_ViewController:
-(IBAction)someButtonClick
{
[self.navigationController pushViewController:C_Controller animated:YES];
}
In C_ViewController:
-(IBAction)someButtonClick
{
[self.navigationController popToRootViewControllerAnimated:YES];
}
Problem:
A_viewController -> B_viewController -> C_viewController is fine.
but after popToRootViewController to A From C, A can't push to B anymore.
and other pushViewController: all can't works, popViewControllerAnimated: also cause crash.
Note.
have tried
// in A view
dispatch_async(dispatch_get_main_queue(),^{
[self.navigationController pushViewController:B_viewController animated:YES];
})
in this post, but it doesn't works for me.
does anyone know what happens in view controller stacks?
have struggling in this issue all day, any help will be appreciated!

Answer 1

When you When you popToViewController from C, the viewWillAppear method will in A be called just before the animation. Now, at this point, since the transition is in progress, you might get some kind of warning in the debugger like:
"Warning: Attempting to push .... while a transition is in progress"
You need to call the navigation controller methods in such a way that they do not overlap each other.
Calling pushViewController in the viewDidAppear method of A would be better in this context.