Skip to content

Instantly share code, notes, and snippets.

Embed
What would you like to do?
NavigationControllerObserver
import Foundation
public protocol NavigationControllerObserverDelegate : class {
/**
Callback when a `viewController` is popped from the `navigationController` stack
- parameter observer: the observer that observed the pop transition
- parameter viewController: the `UIViewController` that has been popped from the stack
*/
func navigationControllerObserver(_ observer: NavigationControllerObserver,
didObservePopTransitionFor viewController: UIViewController)
}
// We can't use Weak<T: AnyObject> here because we would have
// to declare NavigationControllerObserverDelegate as @objc
private class NavigationControllerObserverDelegateContainer {
private(set) weak var value: NavigationControllerObserverDelegate?
init(value: NavigationControllerObserverDelegate) {
self.value = value
}
}
/**
The `NavigationControllerObserver` class provides a simple API to observe the
pop transitions that occur in a `navigationController` stack.
One drawback of `UINavigationController` is that its delegate is shared among multiple
view controllers and this requires a lot of bookkeeping to register multiple delegates.
`NavigationControllerObserver` allows to register a delegate per viewController we want to observe.
What's more the class provides a `navigationControllerDelegate` property used to forward all the
`UINavigationControllerDelegate` methods to another navigationController delegate if need be.
- important: The `NavigationControllerObserver` will observe only *animated* pop transitions.
Indeed, if you call `popViewController(animated: false)` you won't be notified.
*/
public class NavigationControllerObserver : NSObject, UINavigationControllerDelegate {
/**
All calls from `UINavigationControllerDelegate` methods are forwarded to this object
*/
public weak var navigationControllerDelegate: UINavigationControllerDelegate? {
didSet {
// Make the navigationController reevaluate respondsToSelector
// for UINavigationControllerDelegate methods
navigationController.delegate = nil
navigationController.delegate = self
}
}
private var viewControllersToDelegates: [UIViewController: NavigationControllerObserverDelegateContainer] = [:]
private let navigationController: UINavigationController
/**
- parameter navigationController: the `UINavigationController` we want to observe
*/
public init(navigationController: UINavigationController) {
self.navigationController = navigationController
super.init()
navigationController.delegate = self
}
//MARK: - NSObject
override public func responds(to aSelector: Selector!) -> Bool {
if shouldForwardSelector(aSelector) {
return navigationControllerDelegate?.responds(to: aSelector) ?? false
}
return super.responds(to: aSelector)
}
override public func forwardingTarget(for aSelector: Selector!) -> Any? {
if shouldForwardSelector(aSelector) {
return navigationControllerDelegate
}
return super.forwardingTarget(for: aSelector)
}
//MARK: - Public
/**
Observe a pop transition in the `navigationController` stack
- parameter viewController: the `UIViewController` instance to observe in the `navigationController` stack
- parameter delegate: The delegate that will be notified of the transition
*/
public func observePopTransition(of viewController: UIViewController,
delegate: NavigationControllerObserverDelegate) {
let wrappedDelegate = NavigationControllerObserverDelegateContainer(value: delegate)
viewControllersToDelegates[viewController] = wrappedDelegate
}
//MARK: - UINavigationControllerDelegate
public func navigationController(_ navigationController: UINavigationController,
didShow viewController: UIViewController,
animated: Bool) {
navigationControllerDelegate?.navigationController?(
navigationController,
didShow: viewController,
animated: animated
)
guard
let fromViewController = navigationController.transitionCoordinator?.viewController(forKey: .from),
!navigationController.viewControllers.contains(fromViewController) else {
return
}
if let wrappedDelegate = viewControllersToDelegates[fromViewController] {
let delegate = wrappedDelegate.value
delegate?.navigationControllerObserver(self, didObservePopTransitionFor: fromViewController)
viewControllersToDelegates.removeValue(forKey: fromViewController)
}
cleanOutdatedViewControllers()
}
//MARK: - Private
private func shouldForwardSelector(_ aSelector: Selector!) -> Bool {
let description = protocol_getMethodDescription(UINavigationControllerDelegate.self, aSelector, false, true)
return
description.name != nil // belongs to UINavigationControllerDelegate
&& class_getInstanceMethod(type(of: self), aSelector) == nil // self does not implement aSelector
}
private func cleanOutdatedViewControllers() {
let viewControllersToRemove = viewControllersToDelegates.keys.filter {
$0.parent != self.navigationController
}
viewControllersToRemove.forEach {
viewControllersToDelegates.removeValue(forKey: $0)
}
}
}
@chosa91

This comment has been minimized.

Copy link

@chosa91 chosa91 commented Oct 12, 2018

Instead of NavigationControllerObserverDelegateContainer maybe you could use NSMapTable

Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment