NavigatableRIBs

A problem what I want to solve

• When using UINavigationController, we typically invoke popViewController through an action event or simply by swiping back from left to right. This process automatically deallocates the topViewController of the UINavigationController, eliminating the need for manual memory management.
• When I attempted this with the RIBs framework, I encountered some issues. The detachChild method of the router cannot be called directly because the framework does not capture the pop swipe gesture. This limitation leads to a memory leak bug.
• Unfortunately, the RIBs framework's examples do not include any navigation examples or solutions. As a result, some developers typically resort to using the viewDidAppear method of UIViewController for supporting pop swipe gesture.
• However, I believe that such implementations indicate a lack of proper understanding of the method's intended purpose. This approach can increase complexity and lead to unexpected errors.

The goal

• Let’s solve the problem with UIViewController’s life cycle.
• Let’s handle all navigation cases.
  • Simply call the popViewController method.
  • Support swipe-back gesture.
  • Support multiple view controllers deallocation case when either the UITabbar button is clicked or the navigation back button’s long click occured.
• Minimize the implementation requirements to the end users.

Implementations

1. First, We have to know the basic parts of a RIBs.

   

   • Router: A Router listens to the Interactor and translates its outputs into attaching and detaching child RIBs.
   • View(View Controller): Views build and update the UI. Views are designed to be as “dumb” as possible. They just display information.

2. Second, We have to know the life cycle of UINavigationController.

   

   • When UINavigationController pops the UIViewController-C, the delegate method navigationController(_:didShow:animated:) is called, with the didShow parameter specifically indicating the UIViewController that was shown.

3. As a result,

   

   • When the navigationController(_:didShow:animated:) is called, it is necessary to locate the RIB family(especially the Router) associated with the didShow UIViewController. Subsequently, we should invoke the detach method to remove child elements from the memory.

4. As a code

   • Create a common UINavigationController and set it to delegate to itself. We define a cachedViewController property to call detach method.

   • When the navigationController(_:didShow:animated:) is called, we handle it based on whether it confirms to the RIBs framework.

     public class CommonRIBNavigationController: UINavigationController, UINavigationControllerDelegate {
     
     private var cachedViewController: [UIViewController] = []
     
     public override func viewDidLoad() {
         super.viewDidLoad()
         self.delegate = self
     }
     
     public override func pushViewController(_ viewController: UIViewController, animated: Bool) {
         
         super.pushViewController(viewController, animated: animated)
         
         if cachedViewController.contains(viewController) == false {
             cachedViewController.append(viewController)
         }
     }
     
     public func navigationController(_ navigationController: UINavigationController, didShow viewController: UIViewController, animated: Bool) {
         
         guard cachedViewController.count > children.count else { return }
         
         guard let currentIndex = cachedViewController.firstIndex(of: viewController), cachedViewController.count > currentIndex + 1 else { return }
         
         //  When the last dismissed view controller is kind of a RIBs and CommonRIBsViewController.
         guard cachedViewController[currentIndex + 1] is ViewControllable, let current = cachedViewController[currentIndex] as? CommonRIBsViewController else {
             cachedViewController = Array(cachedViewController[0...currentIndex])
             return
         }
         
         current.resourceFlusher?.flushRIBsResources()
         cachedViewController = Array(cachedViewController[0...currentIndex])
     }
     

   • Create a common UIViewController and Router(RIBs).

     • CommonRIBsViewController: In this scenario, it must identify the appropriate router to release the resources of the child RIBs.
     • CommonRIBsRouter: Using common router is mandatory to find and release RIBs resources.

       public protocol CommonRIBsInteractable: Interactable {
           var resourceFlusher: CommonRIBsResourceFlush? { get }
       }
       
       public protocol CommonRIBsResourceFlush {
           func flushRIBsResources()
       }
       
       public class CommonRIBsViewController: UIViewController, ViewControllable {
           
           public var resourceFlusher: CommonRIBsResourceFlush? {
               nil
           }
       }
       
       public class CommonRIBsRouter<InteractorType, ViewControllerType>: ViewableRouter<InteractorType, ViewControllerType>, CommonRIBsResourceFlush {
           
           public var nextScreenRouter: ViewableRouting?
           
           /**
             Easy short-cut push method to use same router.
           */
           @discardableResult
           public func push(nextRouter: ViewableRouting?, animated: Bool) -> Bool {
               
               if nextScreenRouter != nil {
                   flushRIBsResources()
               }
               
               guard let next = nextRouter else { return false }
               
               nextScreenRouter = next
               nextScreenRouter?.interactable.activate()
               nextScreenRouter?.load()
               
               viewControllable.uiviewController.navigationController?.pushViewController(next.viewControllable.uiviewController, animated: animated)
               return true
           }
       
           /**
             Deactivate RIBs resource and set nil
           */
           public func flushRIBsResources() {
               
               nextScreenRouter?.interactable.deactivate()
               nextScreenRouter = nil
           }
       }

   • Example

     final class MasterViewController: CommonRIBsViewController, MasterPresentable {
     
         override var resourceFlusher: CommonRIBsResourceFlush? {
     
             guard let listener = listener as? CommonRIBsInteractable else { return nil }
             return listener.resourceFlusher
         }
     		
         // ... Do other things...   
     }
     
     protocol MasterInteractable: CommonRIBsInteractable {
         // ... Do other things...
     }
     
     final class MasterInteractor: PresentableInteractor<MasterPresentable>, MasterInteractable {
         
         public var resourceFlusher: CommonRIBsResourceFlush? {
             router as? CommonRIBsResourceFlush
         }
     
         // ... Do other things...
     }
     
     final class MasterRouter: CommonRIBsRouter <MasterInteractable, ViewControllable>, MasterRouting, LaunchRouting {
         
         // ... Do other things...
         func routeToDetail(at case: MasterExampleCase) {
             
             let detail = DetailBuilder(dependency: EmptyComponent()).build(`case`)
             // Use common push method.`
             push(nextRouter: detail, animated: true)
         }
     }

Technologies

• Notion Blog
• RIBs
• Engineering the Architecture Behind Uber’s New Rider App
• UINavigationControllerDelegate
• UIViewControllerAnimatedTransitioning
• View Controller Programming Guide for iOS