How to get root view controller?

if you are trying to access the rootViewController you set in your appDelegate. try this:

Objective-C

YourViewController *rootController = (YourViewController*)[[(YourAppDelegate*)
                                   [[UIApplication sharedApplication]delegate] window] rootViewController];

Swift

let appDelegate  = UIApplication.sharedApplication().delegate as AppDelegate
let viewController = appDelegate.window!.rootViewController as YourViewController

Swift 3

let appDelegate  = UIApplication.shared.delegate as! AppDelegate
let viewController = appDelegate.window!.rootViewController as! YourViewController

Swift 4 & 4.2

let viewController = UIApplication.shared.keyWindow!.rootViewController as! YourViewController

Swift 5 & 5.1 & 5.2

let viewController = UIApplication.shared.windows.first!.rootViewController as! YourViewController

Objective-C

UIViewController *controller = [UIApplication sharedApplication].keyWindow.rootViewController;

Swift 2.0

let viewController = UIApplication.sharedApplication().keyWindow?.rootViewController

Swift 5

let viewController = UIApplication.shared.keyWindow?.rootViewController

As suggested here by @0x7fffffff, if you have UINavigationController it can be easier to do:

YourViewController *rootController =
    (YourViewController *)
        [self.navigationController.viewControllers objectAtIndex: 0];

The code in the answer above returns UINavigation controller (if you have it) and if this is what you need, you can use self.navigationController.