Get top UIViewController from different UINavigationController without reference

Question

I've a view hierarchy

a) UINavigationController > b) UIViewController > c) UITabbarController > d) UINavigationController

Ok, now at any point in app, I'm in b | c | d – I've added notifications to handle (and check) if a user goes (or comes) to background/foreground.

This works great, but if a user comes to foreground – I'm presenting a UIViewController (lets name it 'z') in a different (new) UINavigationController object.

This is also works great.. but heres' the problem if I'm already in z and user go background and the comes to foreground, I should not show z again as its already visible.

Problem I'm facing :

• I don't keep reference of that different (new) UINavigationController object or even reference of z.

• So – how do I catch that currently visible view is z itself?

If its from same navigation controller (like a) I may detect it by its property topViewController . But here I can't?

Any way to get this done wihtout creating reference for it?

Answer 1

You can present the controller(zController in your case) on window's root view controller and check if its already presented.

Present the controller on root view controller,

//Use this code to present the zController
    UIViewController *rootViewController =[[[[UIApplication sharedApplication] delegate] window] rootViewController];
    [rootViewController presentViewController:zController animated:YES completion:nil];

and when application enters foreground, you can check if the controller is already presented as follows,

- (BOOL)checkIfzControllerIsAlreadyPresented
{
    UIViewController *rootViewController =[[[[UIApplication sharedApplication] delegate] window] rootViewController];
    id obj = rootViewController.presentedViewController;
    if (obj && [obj isKindOfClass:[zController class]]) {
        return YES; //zController is already visble
    }
    return NO;
}