App delegate without storyboards

AppDelegate.swift

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {
    lazy var window: UIWindow? = {
        let window = UIWindow(frame: UIScreen.mainScreen().bounds)
        window.backgroundColor = UIColor.whiteColor()
        window.rootViewController = ViewController()
        return window
    }()

    func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {
        window!.makeKeyAndVisible()
        return true
    }
}