iOS - Split View Controller - How do I get a pointer (reference) to the Detail View Controller from inside the Master View Controller?

Split view controllers do have references to their master and detail view controllers, via the viewControllers property.

In iOS 7.x and below, the viewControllers array should have exactly two view controller objects in it. The first object is the master view controller and the second object is the detail view controller.

In iOS 8.0 and above, the viewControllers array has at least one view controller object in it – the master (or "primary") view controller. If a second view controller object is in the array, then it is the detail (or "secondary") view controller. When the split view controller is collapsed, only the master view controller is in this array, and when expanded it will contain both the master and the detail view controllers.

You can use the splitViewController property of all view controllers to get your split view controller, and from there use the viewControllers property to access either your master or detail view controllers, like so:

Swift:

let masterVC = self.splitViewController?.viewControllers.firstlet detailVC = (self.splitViewController?.viewControllers.count > 1) ? self.splitViewController?.viewControllers[1] : nil

Objective-C:

UIViewController *masterVC = [self.splitViewController.viewControllers firstObject];UIViewController *detailVC;if (self.splitViewController.viewControllers.count > 1) {    detailVC = self.splitViewController.viewControllers[1];}

The splitViewController property works by walking up the view controller hierarchy and trying to find any split view controller that the calling view controller is in. If the view controller is not in a split view controller, then the property is nil. It works the same as the navigationController and tabBarController view controller properties.

You can make the master and detail view controllers easier to access using an extension in Swift (or a category in Objective-C) on UISplitViewController, like so (replacing all the xx_'s with your own prefix if you're using Objective-C):

Swift:

extension UISplitViewController {    var primaryViewController: UIViewController? {        return self.viewControllers.first    }    var secondaryViewController: UIViewController? {        return self.viewControllers.count > 1 ? self.viewControllers[1] : nil    }}

Objective-C:

// UISplitViewController+ChildViewControllerAccess.h@interface UISplitViewController (ChildViewControllerAccess)@property (nonatomic, readonly) UIViewController *xx_primaryViewController;@property (nonatomic, readonly) UIViewController *xx_secondaryViewController;@end// UISplitViewController+ChildViewControllerAccess.m@implementation UISplitViewController (ChildViewControllerAccess)- (UIViewController *)xx_primaryViewController{    return self.viewControllers.firstObject;}- (UIViewController *)xx_secondaryViewController{    return self.viewControllers.count > 1 ? self.viewControllers[1] : nil;}@end

You can then make use of these properties like so:

Swift:

func someFunctionInSomeViewControllerClass {    // Get the primary and secondary view controllers if    // this view controller is in a split view controller.    // These will be nil if this view controller is not a    // descendant of a split view controller.    var primaryVC = self.splitViewController?.primaryViewController    var secondaryVC = self.splitViewController?.secondaryViewController    // Do something with them    primaryVC?.title = "This is the primary VC"    secondaryVC?.title = "This is the secondary VC"}

Objective-C:

#import "UISplitViewController+ChildViewControllerAccess.h"[...]- (void)someMethodInSomeViewControllerClass{    // Get the primary and secondary view controllers if    // this view controller is in a split view controller.    // These will be nil if this view controller is not a    // descendant of a split view controller.    UIViewController *primaryVC = self.splitViewController.xx_primaryViewController;    UIViewController *secondaryVC = self.splitViewController.xx_secondaryViewController;    // Do something with them    primaryVC.title = @"This is the primary VC";    secondaryVC.title = @"This is the secondary VC";}

If you are using iOS 14+, you can get a specific viewController from splitViewController using viewController(for:) method:

let detailViewController = splitViewController.viewController(for: .secondary) as? DetailViewController

Create a property in your UISplitViewController subclass:

var _detailViewController: UIViewController? {    get {        if viewControllers.count > 1 {            return viewControllers[1] as? UIViewController        }        return nil    }}

According to Apple's documentation, this should sometimes return nil, but in my experience, it always returns the detail view controller, regardless of state.

Also, do not call this property "detailViewController" instead of "_detailViewController" - Apple is apparently already using that name under the hood, and it will mess with your UI.

UISplitViewController is really hokey and needs a lot of cleanup and corrected documentation...