Possible "direct binding" between ViewModel object and View? about swiftui-architectures

[pauljohanneskraft]

Hey @Devepre !

I was also wondering about this problem. Since in ViewState MVVM there should only be a read-only state available to the view and all state changes should be initiated by an input being triggered. Therefore, I would suggest the following extension to create bindings. To make this API even easier to use, you can create extensions using keypaths as well, just as an example.

extension AnyViewModel {
    func bind<Value>(_ value: @escaping (State) -> Value,
                     to input: @escaping (Value) -> Input?) -> Binding<Value> {

        Binding(get: { value(self.state) },
                set: { input($0).map { self.trigger($0) } })
    }
}

This would allow you to create bindings like the following for a text property of your state and an input for that property:

viewModel.bind({ $0.text }, to: { .text($0) })

In your viewModel, you can then change the state depending on that input - that may be a bit of an overhead, but it would ensure that the viewModel state is read-only. Another option would be to make the state read-write and then ensuring that you are only writing to the state, whenever it would seriously impact code overhead.

[Devepre]

Hi @pauljohanneskraft ,

Sounds reasonable, thanks a lot!

I've tried both approaches a little bit in practice. For now, second approach with read-write state and KeyPaths "everywhere" is more enjoyable to me, because of cleaner API and less boilerplate code. It will look like this code snippet:

viewModel.bind(on: \.text)

Also it's critical to have read-only state, that's why I've used private(set) var state but func forceUpdate(_ newState: State) as ViewModel protocol requirement while AnyViewModel's implementation will assert failure.

[savage7]

@Devepre
Could you be so kind to share how you realized this?
viewModel.bind(on: \.text)

[Devepre]

@savage7 it was tricky task, since I've moved to another approach a long time ago and didn't have commits pushed to the server. Anyway I've managed to find my old implementation. If it makes sense, I can make pull request to the original repo, anyway you can take a look implementation in forked version here https://github.com/Devepre/SwiftUI-Architectures/tree/develop commit c69e644e6dfac461e172adb1804723b50c4eba01