Scene Coordinator

화면 전환을 처리하는 Scene Coordinator

1. 화면전환 열거형 구현

import Foundation

enum TransitionStyle {
    case root //첫번째 화면 표시
    case push
    case modal
}

enum TransitionError: Error {
    case navigationControllerMissing
    case cannotPop
    case unknown
}

2. Scene 생성 구현

import UIKit

enum Scene {
    case list(MemoListViewModel)
    case detail(MemoDetailViewModel)
    case compse(MemoComposeViewModel)
}

extension Scene {
    //스토리보드에 있는 씬 생성. 연관값에 저장된 뷰모델 바인딩 후 리턴
    func instantiate(from storyboard: String = "Main") -> UIViewController {
        let storyboard = UIStoryboard(name: storyboard, bundle: nil)
        
        switch self {
        case .list(let memoListViewModel):
            guard let nav = storyboard.instantiateViewController(withIdentifier: "ListNav") as? UINavigationController else {
                fatalError()
            }
            
            guard var listVC = nav.viewControllers.first as? MemoListViewController else {
                fatalError()
            }
            
            listVC.bind(viewModel: memoListViewModel)
            
            return nav
            
        case .detail(let memoDetailViewModel):
            guard var detailVC = storyboard.instantiateViewController(withIdentifier: "DetailVC") as? MemoDetailViewController else {
                fatalError()
            }
            
            detailVC.bind(viewModel: memoDetailViewModel)
            
            return detailVC
            
        case .compse(let memoComposeViewModel):
            guard let nav = storyboard.instantiateViewController(withIdentifier: "ComposeNav") as? UINavigationController else {
                fatalError()
            }
            
            guard var composeVC = nav.viewControllers.first as? MemoComposeViewController else {
                fatalError()
            }
            
            composeVC.bind(viewModel: memoComposeViewModel)
            
            return nav
        }
    }
}

3. SceneCoordinator protocol 선언 및 구현

import Foundation
import RxSwift

protocol SceneCoordinatorType {
    @discardableResult
    func transition(to scene: Scene, using style: TransitionStyle, animated: Bool) -> Completable
    
    @discardableResult
    func close(animated: Bool) -> Completable
}

import Foundation
import RxSwift
import RxCocoa

class SceneCoordinator: SceneCoordinatorType {
    private let bag = DisposeBag()
    
    //화면전환을 처리하기 때문에 Window인스턴스와 현재 화면에 표시되어있는 Scene을 가지고 있어야 함
    private var window: UIWindow
    private var currentVC: UIViewController
    
    required init(window: UIWindow) {
        self.window = window
        currentVC = window.rootViewController!
    }
    
    @discardableResult
    func transition(to scene: Scene, using style: TransitionStyle, animated: Bool) -> RxSwift.Completable {
        let subject = PublishSubject<Never>() //성공과 실패만 방출하므로 Never 사용
        
        let target = scene.instantiate()
        
        switch style {
        case .root:
            currentVC = target
            window.rootViewController = target
            
            subject.onCompleted()
            
        case .push:
            guard let nav = currentVC.navigationController else {
                subject.onError(TransitionError.navigationControllerMissing)
                break
            }
            
            nav.pushViewController(target, animated: animated)
            currentVC = target
            
            subject.onCompleted()
            
        case .modal:
            currentVC.present(target, animated: animated) {
                subject.onCompleted()
            }
            currentVC = target
        }
        
        return subject.asCompletable()
    }
    
    @discardableResult
    func close(animated: Bool) -> RxSwift.Completable {
        return Completable.create { [unowned self] completable in
            if let presentingVC = self.currentVC.presentingViewController {
                self.currentVC.dismiss(animated: animated) {
                    self.currentVC = presentingVC
                    completable(.completed)
                }
            }
            
            else if let nav = self.currentVC.navigationController {
                guard nav.popViewController(animated: animated) != nil else {
                    completable(.error(TransitionError.cannotPop))
                    return Disposables.create()
                }
                
                self.currentVC = nav.viewControllers.last!
                completable(.completed)
            }
            
            else {
                completable(.error(TransitionError.unknown))
            }
            
            return Disposables.create()
        }
    }
    
}