Switch root view controller

[Swift] Switch-RootViewController

func switchRootViewController(rootViewController: UIViewController, animated: Bool, completion: (() -> Void)?) {
        if animated {
            UIView.transitionWithView(window, duration: 0.5, options: .TransitionCrossDissolve, animations: {
                let oldState: Bool = UIView.areAnimationsEnabled()
                UIView.setAnimationsEnabled(false)
                self.window!.rootViewController = rootViewController
                UIView.setAnimationsEnabled(oldState)
            }, completion: { (finished: Bool) -> () in
                if completion {
                    completion!()
                }
            })
        } else {
            window!.rootViewController = rootViewController
        }
    }

Make completion parameter optional.

    func switchRootViewController(rootViewController: UIViewController, animated: Bool, completion: (() -> Swift.Void)? = nil) {
      ...
    )

Warning: 'keyWindow' was deprecated in iOS 13.0: Should not be used for applications that support multiple scenes as it returns a key window across all connected scenes

What is the replacement for this? Any solution?

try this!

    let scene = UIApplication.shared.connectedScenes.first
    guard let windowScene = (scene as? UIWindowScene) else { return }
    let window = UIWindow(windowScene: windowScene)

My solution is very simple. Inside your SceneDelegate.swift file add your function to update root view controller.
For example this is my function to change root widow to tab bar controller.

// SceneDelegate.swift

    func moveToTabBarController() {
        window?.rootViewController = createTabBar()
        window?.makeKeyAndVisible()
    }

And inside your view controller you can get access to scene delegate and call your change controller function.

   let sceneDelegate = self.view.window?.windowScene?.delegate as! SceneDelegate
   sceneDelegate.moveToTabBarController()

If you have sceneDelegate in your project use this:

let sb = UIStoryboard(name: "Main", bundle: nil)
let VC = sb.instantiateViewController(withIdentifier: "LoginViewController") as! LoginViewController
let navRootView = UINavigationController(rootViewController: VC)
self.present(navRootView, animated: true, completion: nil)

Swift 5.1

extension UIWindow {
    
    func switchRootViewController(_ viewController: UIViewController,
                                  animated: Bool = true,
                                  duration: TimeInterval = 0.5,
                                  options: AnimationOptions = .transitionFlipFromRight,
                                  completion: (() -> Void)? = nil) {
        guard animated else {
            rootViewController = viewController
            return
        }
        
        UIView.transition(with: self, duration: duration, options: options, animations: {
            let oldState = UIView.areAnimationsEnabled
            UIView.setAnimationsEnabled(false)
            self.rootViewController = viewController
            UIView.setAnimationsEnabled(oldState)
        }, completion: { _ in
            completion?()
        })
    }
    
}

Swift 5.1

extension UIWindow {
    
    func switchRootViewController(_ viewController: UIViewController,
                                  animated: Bool = true,
                                  duration: TimeInterval = 0.5,
                                  options: AnimationOptions = .transitionFlipFromRight,
                                  completion: (() -> Void)? = nil) {
        guard animated else {
            rootViewController = viewController
            return
        }
        
        UIView.transition(with: self, duration: duration, options: options, animations: {
            let oldState = UIView.areAnimationsEnabled
            UIView.setAnimationsEnabled(false)
            self.rootViewController = viewController
            UIView.setAnimationsEnabled(oldState)
        }, completion: { _ in
            completion?()
        })
    }
    
}

how I can implement this ?

@jesus003
let loginVC = QGLoginViewController.loadFromNib()
guard let window = self.view.window else {
return
}
window.switchRootViewController(to: loginVC)

Swift 5.5 with the introduction of async/await APIs

extension UIWindow {

    @MainActor
    func setRootViewController(_ newRootViewController: UIViewController, animated: Bool = true) async {
        guard animated else {
            rootViewController = newRootViewController
            return
        }

        await withCheckedContinuation({ (continuation: CheckedContinuation<Void, Never>) in
            UIView.transition(with: self, duration: 0.3, options: .transitionCrossDissolve) {
                let oldState: Bool = UIView.areAnimationsEnabled
                UIView.setAnimationsEnabled(false)
                self.rootViewController = newRootViewController
                UIView.setAnimationsEnabled(oldState)
            } completion: { _ in
                continuation.resume()
            }
        })
    }

}

Crash Occurrence in this method, not regular. Any Idea to fix this sporadic crash..

NSInternalInconsistencyException - Attempting to transfer an animation to an animation state that is not a direct child of the animation's animation state.

Fatal Exception: NSInternalInconsistencyException
0 CoreFoundation 0x92d1c __exceptionPreprocess
1 libobjc.A.dylib 0x14ee4 objc_exception_throw
2 Foundation 0x124c80 _userInfoForFileAndLine
3 UIKitCore 0x5f0658 -[UIViewAnimationState _transferAnimationToTrackingAnimator:]
4 UIKitCore 0x71ee0 __85+[UIViewPropertyAnimator _animationBlockForTrackingAnimation:animator:trackingSetup:]_block_invoke
5 UIKitCore 0x4a3d14 -[UIViewPropertyAnimator _runAnimations]
6 UIKitCore 0x34fba4 __49-[UIViewPropertyAnimator startAnimationAsPaused:]_block_invoke_2
7 UIKitCore 0x206ccc __49-[UIViewPropertyAnimator startAnimationAsPaused:]_block_invoke
8 UIKitCore 0x70754c __49-[UIViewPropertyAnimator startAnimationAsPaused:]_block_invoke.1011
9 UIKitCore 0x510eac -[UIViewPropertyAnimator _setupAnimationTracking:]
10 UIKitCore 0x9c494 -[UIViewPropertyAnimator startAnimationAsPaused:]
11 UIKitCore 0x3396e4 +[UIViewPropertyAnimator _trackAnimationWithAnimator:forLayer:forAnimationKey:trackingSetup:]
12 UIKitCore 0x9c07c +[UIViewPropertyAnimator _trackNonAdditiveAnimationWithAnimator:forLayer:forKey:]
13 UIKitCore 0x58d55c -[UIViewAnimationState pop]
14 UIKitCore 0x25bdb8 +[UIViewAnimationState popAnimationState]
15 UIKitCore 0x1751a8 +[UIView _setupAnimationWithDuration:delay:view:options:factory:animations:start:animationStateGenerator:completion:]