SwiftUIでUndoManagerを試してみる

ContentView.swift

import SwiftUI

struct ContentView: View {
    @ObservedObject var model = Model()
    @State var isOn: Bool = false
    @State var canUndo = false
    @State var canRedo = false

    var body: some View {
        VStack {
            Toggle("On/Off", isOn: $isOn)
            Spacer()
            Button("Undo") {
                model.undo()
            }
            .disabled(!canUndo)
            Button("Redo") {
                model.redo()
            }
            .disabled(!canRedo)
            .onAppear() {
                isOn = model.isOn
                canUndo = model.canUndo
                canRedo = model.canRedo
            }
            .onChange(of: isOn
                      , perform: { newValue in
                model.isOn = isOn
            })
            .onChange(of: model.isOn, perform: { newValue in
                isOn = model.isOn
            })
            .onChange(of: model.canUndo) { newValue in
                canUndo = model.canUndo
            }
            .onChange(of: model.canRedo) { newValue in
                canRedo = model.canRedo
            }
        }
        .padding()
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}

Model.swift

import Foundation

class Model: NSObject, ObservableObject {
    override init() {
        super.init()
    }
    
    private var undoManager = UndoManager()

    var isOn: Bool = false{
        willSet {
            debugPrint("willSet: \(self.isOn) -> \(newValue)")
              objectWillChange.send()
              let v = self.isOn
              debugPrint("regist handler")
              undoManager.registerUndo(withTarget: self, handler: {
                  debugPrint("handle: \($0.isOn) -> \(v)")
                  $0.isOn = v
              })
        }
        didSet {
            debugPrint("didSet: \(self.isOn)")
        }
    }
    
    func undo() {
        undoManager.undo()
    }
    
    func redo() {
        undoManager.redo()
    }
    
    var canUndo: Bool {
        undoManager.canUndo
    }
    
    var canRedo: Bool {
        undoManager.canRedo
    }
    
}