协调器的 RxSwift 并发问题

Question

我想做的事：

1. 介绍 VC1
2. 当 VC1 关闭时，显示 VC2

问题：

1. 当 VC1 关闭时，VC2 不存在

脏修复： 放毫秒延迟。它解决了问题，但想知道它为什么会发生

说明：当 VC1 关闭时，我得到 viewDidDissapear 事件，因此我可以呈现 VC2

如果您需要更多详细信息，请询问。

代码：

class ViewModel {

    let coordinator = Coordinator()

    struct Input {
        let itemSelected: Driver<IndexPath>
    }

    struct Output {
        let presentVC1: Driver<Void>
        let presentVC2: Driver<Void>
    }

    func transform(input: Input) -> Output {

        let navigateToVC1 = input.itemSelected
            .flatMap { [coordinator] in
                return coordinator.transition(to: Scene.VC1)
            }

        let navigateToVC2 = navigateToVC1
            .delay(.milliseconds(1))
            .flatMap { [coordinator] in
                return coordinator.transition(to: Scene.VC2)
            }

        return Output(presentVC1: presentVC1, presentVC2: presentVC2)
    }

协调员代码：

func transition(to scene: TargetScene) -> Driver<Void> {
        let subject = PublishSubject<Void>()

        switch scene.transition {
           
            case let .present(viewController):
                _ = viewController.rx
                    .sentMessage(#selector(UIViewController.viewDidDisappear(_:)))
                    .map { _ in } 
                    .bind(to:subject)
                currentViewController.present(viewController, animated: true)
                
        return subject
            .take(1)
            .asDriverOnErrorJustComplete()
    }

Answer 1

在视图控制器完全关闭之前调用viewDidDisappear 方法。在调用dismiss 的回调之前，您不应尝试呈现第二个视图控制器。

无论您在何处关闭视图控制器，请改用以下内容，并且在 observable 发出下一个事件之前不要显示下一个视图控制器。

extension Reactive where Base: UIViewController {
    func dismiss(animated: Bool) -> Observable<Void> {
        Observable.create { [base] observer in
            base.dismiss(animated: animated) {
                observer.onNext(())
                observer.onCompleted()
            }
            return Disposables.create()
        }
    }
}

我建议您考虑使用我的 Cause-Logic-Effect 架构，其中包含正确处理视图控制器呈现和关闭所需的一切。

https://github.com/danielt1263/CLE-Architecture-Tools

部分界面如下：

/**
Presents a scene onto the top view controller of the presentation stack. The scene will be dismissed when either the action observable completes/errors or is disposed.
- Parameters:
- animated: Pass `true` to animate the presentation; otherwise, pass `false`.
- sourceView: If the scene will be presented in a popover controller, this is the view that will serve as the focus.
- scene: A factory function for creating the Scene.
- Returns: The Scene's output action `Observable`.
*/
func presentScene<Action>(animated: Bool, overSourceView sourceView: UIView? = nil, scene: @escaping () -> Scene<Action>) -> Observable<Action>

extension NSObjectProtocol where Self : UIViewController {

    /**
        Create a scene from an already existing view controller.
    
        - Parameter connect: A function describing how the view controller should be connected and returning an Observable that emits any data the scene needs to communicate to its parent.
        - Returns: A Scene containing the view controller and return value of the connect function.
    
        Example:
    
        `let exampleScene = ExampleViewController().scene { $0.connect() }`
        */
    func scene<Action>(_ connect: (Self) -> Observable<Action>) -> Scene<Action>
}

struct Scene<Action> {
    let controller: UIViewController
    let action: Observable<Action>
}

connect 函数是你的视图模型，当它的 Observable 完成或它的订阅者释放时，视图控制器将自动关闭。

presentScene 函数是您的协调器。它处理场景的实际呈现和解除。当您关闭并呈现一个新场景时，它将正确处理等待，直到前一个视图控制器被关闭后再呈现下一个。