UIWindowTransitions.swift

//
//  UIWindowTransitions.swift
//  Daniele Margutti
//
//  Created by Daniele Margutti.
//  Copyright © 2017 Daniele Margutti. All rights reserved.
//

import Foundation
import UIKit

public extension UIWindow {
	
	/// Transition Options
	public struct TransitionOptions {
		
		/// Curve of animation
		///
		/// - linear: linear
		/// - easeIn: ease in
		/// - easeOut: ease out
		/// - easeInOut: ease in - ease out
		public enum Curve {
			case linear
			case easeIn
			case easeOut
			case easeInOut
			
			/// Return the media timing function associated with curve
			internal var function: CAMediaTimingFunction {
				let key: String!
				switch self {
				case .linear:		key = kCAMediaTimingFunctionLinear
				case .easeIn:		key = kCAMediaTimingFunctionEaseIn
				case .easeOut:		key = kCAMediaTimingFunctionEaseOut
				case .easeInOut:	key = kCAMediaTimingFunctionEaseInEaseOut
				}
				return CAMediaTimingFunction(name: key)
			}
		}
		
		/// Direction of the animation
		///
		/// - fade: fade to new controller
		/// - toTop: slide from bottom to top
		/// - toBottom: slide from top to bottom
		/// - toLeft: pop to left
		/// - toRight: push to right
		public enum Direction {
			case fade
			case toTop
			case toBottom
			case toLeft
			case toRight
			
			/// Return the associated transition
			///
			/// - Returns: transition
			internal func transition() -> CATransition {
				let transition = CATransition()
				transition.type = kCATransitionPush
				switch self {
				case .fade:
					transition.type = kCATransitionFade
					transition.subtype = nil
				case .toLeft:
					transition.subtype = kCATransitionFromLeft
				case .toRight:
					transition.subtype = kCATransitionFromRight
				case .toTop:
					transition.subtype = kCATransitionFromTop
				case .toBottom:
					transition.subtype = kCATransitionFromBottom
				}
				return transition
			}
		}
		
		/// Background of the transition
		///
		/// - solidColor: solid color
		/// - customView: custom view
		public enum Background {
			case solidColor(_: UIColor)
			case customView(_: UIView)
		}
		
		/// Duration of the animation (default is 0.20s)
		public var duration: TimeInterval = 0.20
		
		/// Direction of the transition (default is `toRight`)
		public var direction: TransitionOptions.Direction = .toRight
		
		/// Style of the transition (default is `linear`)
		public var style: TransitionOptions.Curve = .linear
		
		/// Background of the transition (default is `nil`)
		public var background: TransitionOptions.Background? = nil
		
		/// Initialize a new options object with given direction and curve
		///
		/// - Parameters:
		///   - direction: direction
		///   - style: style
		public init(direction: TransitionOptions.Direction = .toRight, style: TransitionOptions.Curve = .linear) {
			self.direction = direction
			self.style = style
		}
		
		public init() { }
		
		/// Return the animation to perform for given options object
		internal var animation: CATransition {
			let transition = self.direction.transition()
			transition.duration = self.duration
			transition.timingFunction = self.style.function
			return transition
		}
	}
	
	
	/// Change the root view controller of the window
	///
	/// - Parameters:
	///   - controller: controller to set
	///   - options: options of the transition
	public func setRootViewController(_ controller: UIViewController, options: TransitionOptions = TransitionOptions()) {
		
		var transitionWnd: UIWindow? = nil
		if let background = options.background {
			transitionWnd = UIWindow(frame: UIScreen.main.bounds)
			switch background {
			case .customView(let view):
				transitionWnd?.rootViewController = UIViewController.newController(withView: view, frame: transitionWnd!.bounds)
			case .solidColor(let color):
				transitionWnd?.backgroundColor = color
			}
			transitionWnd?.makeKeyAndVisible()
		}
		
		// Make animation
		self.layer.add(options.animation, forKey: kCATransition)
		self.rootViewController = controller
		self.makeKeyAndVisible()
		
		if let wnd = transitionWnd {
			DispatchQueue.main.asyncAfter(deadline: (.now() + 1 + options.duration), execute: {
				wnd.removeFromSuperview()
			})
		}
	}
}

internal extension UIViewController {
	
	/// Create a new empty controller instance with given view
	///
	/// - Parameters:
	///   - view: view
	///   - frame: frame
	/// - Returns: instance
	static func newController(withView view: UIView, frame: CGRect) -> UIViewController {
		view.frame = frame
		let controller = UIViewController()
		controller.view = view
		return controller
	}
	
}

@malcommac its really awesome. Since it required few updates in the code I just revised it in my repo after forking it .. please if you see it fit then pull it from or just update those. that would be help full for lot of the beginner developers...
Updated Code of UIWindowTransitions.swift

Thanks

Hi @dipcse07, would you open a PR into the project?