development: updated RootController API

Sources/iOS/NavigationItem.swift

@@ -143,6 +143,7 @@ extension UINavigationItem {
 		}
 	}
 	
+    /// Title text.
 	@nonobjc
 	public var title: String? {
 		get {

Sources/iOS/RootController.swift

@@ -113,25 +113,27 @@ open class RootController: UIViewController {
      the transition animation from the active rootViewController
      to the toViewController has completed.
      */
-	open func transitionFromRootViewController(toViewController: UIViewController, duration: TimeInterval = 0.5, options: UIViewAnimationOptions = [], animations: (() -> Void)? = nil, completion: ((Bool) -> Void)? = nil) {
+	open func transition(to viewController: UIViewController, duration: TimeInterval = 0.5, options: UIViewAnimationOptions = [], animations: (() -> Void)? = nil, completion: ((Bool) -> Void)? = nil) {
 		rootViewController.willMove(toParentViewController: nil)
-		addChildViewController(toViewController)
-		toViewController.view.frame = rootViewController.view.bounds
+		addChildViewController(viewController)
+		viewController.view.frame = rootViewController.view.bounds
         transition(from: rootViewController,
-            to: toViewController,
+            to: viewController,
 			duration: duration,
 			options: options,
 			animations: animations,
 			completion: { [weak self] (result: Bool) in
-				if let s: RootController = self {
-					toViewController.didMove(toParentViewController: s)
+                guard let s = self else {
+                    return
+                }
+                
+                viewController.didMove(toParentViewController: s)
                 s.rootViewController.removeFromParentViewController()
-					s.rootViewController = toViewController
+                s.rootViewController = viewController
                 s.rootViewController.view.clipsToBounds = true
                 s.rootViewController.view.autoresizingMask = [.flexibleWidth, .flexibleHeight]
                 s.rootViewController.view.contentScaleFactor = Device.scale
                 completion?(result)
-				}
 			})
 	}
 	
@@ -171,7 +173,10 @@ open class RootController: UIViewController {
      passed in controller view within the view hierarchy.
      */
 	internal func prepareControllerWithinContainer(viewController: UIViewController?, container: UIView) {
-		if let v: UIViewController = viewController {
+        guard let v = viewController else {
+            return
+        }
+        
         addChildViewController(v)
         container.addSubview(v.view)
         v.didMove(toParentViewController: self)
@@ -179,5 +184,4 @@ open class RootController: UIViewController {
         v.view.autoresizingMask = [.flexibleWidth, .flexibleHeight]
         v.view.contentScaleFactor = Device.scale
 	}
-	}
 }