ios – 手动创建的UIWindow是错误的大小

我正在学习如何在没有Interface Builder(即故事板,xib等)的情况下创建iOS应用程序.下面是我正在使用的基本应用程序委托类.问题是,当显示时,UIWindow不会用完设备的全屏(参见附件截图).这发生在我测试的所有设备和模拟器上.为什么不使用全屏？

import UIKit

@UIApplicationMain
class AppDelegate: UIResponder,UIApplicationDelegate {
  lazy var window: UIWindow? = {
    debugPrint("AppDelegate: Creating Window")

    let screen: UIScreen = UIScreen.mainScreen()
    let window: UIWindow = UIWindow.init(frame: screen.bounds)

    window.backgroundColor = UIColor.whiteColor()

    return window
  }()

  lazy var rootViewController: ShapesViewController = {
    debugPrint("AppDelegate: Creating Root View Controller")

    let rootViewController = ShapesViewController.init(nibName: nil,bundle: nil)

    return rootViewController
  }()

  func application(application: UIApplication,didFinishLaunchingWithOptions launchOptions: [NSObject : AnyObject]?) -> Bool {
    debugPrint("AppDelegate: applicationWillEnterForeground")

    window?.rootViewController = rootViewController
    window?.makeKeyAndVisible()

    return true
  }
}