Get current view controller from the app delegate

Question

I know that to get the current view controller from the app delegate, I can use the navigationController property I have set up for my app. However, it's possible in many places throughout my app that a modal navigation controller could have been presented. Is there any way to detect this from the app delegate, since the current navigation controller will be different from the one to which the app delegate holds a reference?

Answer 1

Great solution in Swift, implement in AppDelegate

func getTopViewController()->UIViewController{
    return topViewControllerWithRootViewController(UIApplication.sharedApplication().keyWindow!.rootViewController!)
}
func topViewControllerWithRootViewController(rootViewController:UIViewController)->UIViewController{
    if rootViewController is UITabBarController{
        let tabBarController = rootViewController as! UITabBarController
        return topViewControllerWithRootViewController(tabBarController.selectedViewController!)
    }
    if rootViewController is UINavigationController{
        let navBarController = rootViewController as! UINavigationController
        return topViewControllerWithRootViewController(navBarController.visibleViewController)
    }
    if let presentedViewController = rootViewController.presentedViewController {
        return topViewControllerWithRootViewController(presentedViewController)
    }
    return rootViewController
}

Objective - C

- (UIViewController*)topViewController {
    return [self topViewControllerWithRootViewController:[UIApplication sharedApplication].keyWindow.rootViewController];
}

- (UIViewController*)topViewControllerWithRootViewController:(UIViewController*)rootViewController {
    if ([rootViewController isKindOfClass:[UITabBarController class]]) {
       UITabBarController* tabBarController = (UITabBarController*)rootViewController;
       return [self topViewControllerWithRootViewController:tabBarController.selectedViewController];
    } else if ([rootViewController isKindOfClass:[UINavigationController class]]) {
      UINavigationController* navigationController = (UINavigationController*)rootViewController;
      return [self topViewControllerWithRootViewController:navigationController.visibleViewController];
     } else if (rootViewController.presentedViewController) {
       UIViewController* presentedViewController = rootViewController.presentedViewController;
       return [self topViewControllerWithRootViewController:presentedViewController];
     } else {
       return rootViewController;
    }
}

Answer 2

You could try getting the top most view by doing:

[[[[UIApplication sharedApplication] keyWindow] subviews] lastObject];

although this view might be invisible or even covered by some of its subviews...

It depends on your UI but it might help.

Answer 3

I suggest you use NSNofiticationCenter.

//in AppDelegate:
@interface AppDelegate()
{
    ...
    id lastViewController;
    ...
}

@implementation AppDelegate
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    ...
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(handleCurrentViewController) name:@"CurrentViewController" object:nil];
    ...
}

- (void)handleCurrentViewController:(NSNotification *)notification {
    if([[notification userInfo] objectForKey:@"lastViewController"]) {
        lastViewController = [[notification userInfo] objectForKey:@"lastViewController"];
    }
}

- (void)applicationDidEnterBackground:(UIApplication *)application
{    
    NSLog(@"last view controller is %@", [(UIViewController *)lastViewController class]);
}
@end

//in every ViewController you want to detect
@implementation SomeViewController
...
- (void) viewWillDisappear:(BOOL)animated {
    [super viewWillDisappear:animated];
    [[NSNotificationCenter defaultCenter] postNotificationName:@"CurrentViewController" object:nil userInfo:[NSDictionary dictionaryWithObjectsAndKeys:self, @"lastViewController", nil]];
}
...
@end

Answer 4

Other solutions above work only partially as complex view hierarchies are not handled (navigation controller integrated in tab bar controller, split view controllers, view containers and also alert controllers could mess things up).

I solve this by keeping a reference of the current view controller in AppDelegate. Every time the view appears I take advantage of viewDidAppear(animated:) and set the reference in the app delegate.

I know the question was about Objective-C, but I can provide only Swift code and I'm sure it will be useful to both types of users.

First: I've implemented a protocol to keep things clean and reusable:

protocol UpdatableViewController {
    func updateUI()
}

Second: I've added a reference to AppDelegate:

var currentViewController: UpdatableViewController?

Third: I set the current view controller in viewDidAppear():

override func viewDidAppear(animated: Bool) {
    super.viewDidAppear(animated)
    let appDelegate = UIApplication.sharedApplication().delegate as? AppDelegate
    appDelegate?.currentViewController = self
}

Fourth:

extension ViewController1: UpdatableViewController {
    func updateUI() {
        print("Implement updating here")
    }
}

Answer 5

Based on the gist here, I made a category to obtain the top most view controller, such that calling [[UIApplication sharedApplication] topMostViewController] will give you the top most view controller in your app.

This is especially useful in iOS 8 where UIAlertView and UIActionSheet have been deprecated in favor of UIAlertController, which needs to be presented on the top most view controller.

UIViewController+TopMostViewController.h

#import <UIKit/UIKit.h>

@interface UIViewController (TopMostViewController)

- (UIViewController *)topMostViewController;

@end

@interface UIApplication (TopMostViewController)

- (UIViewController *)topMostViewController;

@end

UIViewController+TopMostViewController.m

#import "UIViewController+TopMostViewController.h"

@implementation UIViewController (TopMostViewController)

- (UIViewController *)topMostViewController
{
    if (self.presentedViewController == nil)
    {
        return self;
    }
    else if ([self.presentedViewController isKindOfClass:[UINavigationController class]])
    {
        UINavigationController *navigationController = (UINavigationController *)self.presentedViewController;
        UIViewController *lastViewController = [[navigationController viewControllers] lastObject];
        return [lastViewController topMostViewController];
    }

    UIViewController *presentedViewController = (UIViewController *)self.presentedViewController;
    return [presentedViewController topMostViewController];
}

@end

#pragma mark -

@implementation UIApplication (TopMostViewController)

- (UIViewController *)topMostViewController
{
    return [self.keyWindow.rootViewController topMostViewController];
}

@end

Answer 6

Below code works very well.

+(UIViewController*) findBestViewController:(UIViewController*)vc {

if (vc.presentedViewController) {

    // Return presented view controller
    return [AppDelegate findBestViewController:vc.presentedViewController];

} else if ([vc isKindOfClass:[UISplitViewController class]]) {

    // Return right hand side
    UISplitViewController* svc = (UISplitViewController*) vc;
    if (svc.viewControllers.count > 0)
        return [AppDelegate findBestViewController:svc.viewControllers.lastObject];
    else
        return vc;

} else if ([vc isKindOfClass:[UINavigationController class]]) {

    // Return top view
    UINavigationController* svc = (UINavigationController*) vc;
    if (svc.viewControllers.count > 0)
        return [AppDelegate findBestViewController:svc.topViewController];
    else
        return vc;

} else if ([vc isKindOfClass:[UITabBarController class]]) {

    // Return visible view
    UITabBarController* svc = (UITabBarController*) vc;
    if (svc.viewControllers.count > 0)
        return [AppDelegate findBestViewController:svc.selectedViewController];
    else
        return vc;

} else {

    // Unknown view controller type, return last child view controller
    return vc;

}

}

+(UIViewController*) currentViewController {

// Find best view controller
UIViewController* viewController = [UIApplication sharedApplication].keyWindow.rootViewController;
return [AppDelegate findBestViewController:viewController];

}