iOS View Controllers

View Controllers

• Changing the root view controller

Lifecycle Methods

viewWillAppear

override func viewWillAppear(animated: Bool) {
    // Start any tasks such as polling timers.
    // E.g., a poller that fetching images from an external service.
    super.viewWillAppear(animated)
}

didReceiveMemoryWarning

override func didReceiveMemoryWarning() {
    /*
        iOS will send a warning to an app before it kills the app's
        process.  This is an opportunity to free memory to avoid
        termination.

        E.g., clearing image caches.
    */
    super.didReceiveMemoryWarning()
}

loadView

override func loadView() {
    // Instantiate a custom view and set the controller's root view.
    let customView = MyCustomView()
    view = customView
}

Changing the root view controller

// In AppDelegate.swift

/*
    `window` is an optional public property that the
    UIApplicationDelegate protocol defines.

    when the application instantiates the app delegate class,
    it looks for the app delegate's `window` property.

    if `nil`, it creates the window.
*/
var window: UIWindow?

func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {
    // Remove the custom iOS target property: `Main storyboard file base name`
    // since the main storyboard is not being used to specify the app's entry point.
    let storyboard = UIStoryboard.init(name: "Main", bundle: nil)

    // Creates an instance of a controller that contains IBOutlets.
    // I.e., any controller that connects properties to object in a storyboard
    // or xib/nib file.
    let homeController =
        storyboard.instantiateViewControllerWithIdentifier(
            "homeController"
        ) as! HomeController

    /*
        A UIScreen contains properties associated with a display (hardware)
        An iOS device has one main screen and optional attached screens.

        `UIScreen#bounds` returns a `CGRect`, which describes the screen dimensions in points.
    */
    self.window = UIWindow(frame: UIScreen.mainScreen().bounds)

    if let window = self.window {
        window.rootViewController = homeController
        window.makeKeyAndVisible()
    }

    return true
}

References

• Apple Developer
  • UIScreen
  • UIWindow
• How is the main UIWindow Instantiated - StackOverflow
• makeKeyAndVisible - StackOverflow

References

• Apple Developer
  • View Controllers