ModalViewController overlaps navigationbar even after setting its frame iphone

In my application, I'm launching a modalViewController on rightbarbutton click of navigationbar. This modalViewController overlaps the navigationbar. I tried setting its frame but it remained the same. I want to display navigationbar even if modalViewController is still there.

EDIT: I call the following method on navigationcontroller's rightbarbutton press. The view appears properly but the position is not right.

-(void)showViewForPosts{

self.navigationItem.backBarButtonItem =
[[UIBarButtonItem alloc] initWithTitle:@"DISMISS"开发者_如何学编程
                                 style: UIBarButtonItemStyleBordered
                                target:self
                                action:@selector(dismissViewCOntroller)];

displayController = [[UIViewController alloc]initWithNibName:nil bundle:nil];
displayController.view.frame = CGRectMake(0.0, 150.0, 320, 436);
displayController.view.backgroundColor = [UIColor blueColor];

//I'M ADDING DIFFERENT VIEWS HERE

[self presentModalViewController:displayController animated:YES];
}

Thanx in advance.

Do you need it to be the same navigation bar?

In my app, there is another NavigationController for the modal view flow, ie going from a modal view to another. This feels more consistent to me, since 'modal' means taking (temporary) exclusive access to screen and inputs, whereas navigation on iPhone is stacking views.