Viewにassign(_, to:)メソッド作ってみた #swiftui #CodePiece

CodePiece.swift

import UIKit
import SwiftUI
import Combine

protocol UsecaseProtocol: AnyObject {
    var intPublisher: AnyPublisher<Int, Never> { get }
    func reset()
}

struct ContentView : View {
    
    private let usecase: UsecaseProtocol
    @State var int: Int = 0
    
    init(usecase: UsecaseProtocol) {
        self.usecase = usecase
    }
    
    var body: some View {
        Button.init(action: { [unowned usecase] in
            usecase.reset()
        }, label: {
            Text("\(int)")
        })
            .assign(usecase.intPublisher, to: $int)
    }
    
}

#if DEBUG
let someUsecase = SomeUsecase()
struct ContentView_Previews : PreviewProvider {
    static var previews: some View {
        ContentView(usecase: someUsecase)
    }
}
#endif

private extension View {
    
    func assign <P> (_ publisher: P, to state: Binding<P.Output>) -> SubscriptionView<Publishers.ReceiveOn<P, DispatchQueue>, Self> where P : Publisher, P.Failure == Never {
        return onReceive(publisher.receive(on: DispatchQueue.main)) { result in
            state.value = result
        }
    }
    
}