Only pass changed values in newState

[dav92lee]

Is there a way to only receive the properties that have changed in the newState function? I was looking at the code in https://github.com/ReSwift/ReSwift/blob/937c628a1a9306d70f86c7c6c79c4f5ae38a0ad7/ReSwift/CoreTypes/Subscription.swift however I couldn't seem to figure it out

[mjarvis]

@dav92lee by default, if the state you select is Equatable, then ReSwift will skip repeats.
If you want to manually control this process, you can use the skipRepeats function yourself:

store.subscribe(self) {
    $0.select { $0.substate }.skipRepeats { old, new in old.something == new.something }
}

if you're using latest ReSwift master, then you can also use skip(when: ...) or only(when: ...) which are simple helpers for skipRepeats, and you can also choose to disable the automatic skipping via store.subscriptionsAutomaticallySkipRepeats

[dav92lee]

Thanks for such a quick reply!

when i throw that code

    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        mainStore.subscribe(self) {
            $0.select { $0.substate }.skipRepeats { old, new in old.something == new.something }
        }
    }

I get the error:

Cannot invoke 'subscribe' with an argument list of type '(TopBarVC, (_) -> _)'

Can i not do this when subclass StoreSubscriber in a UIViewController?

Thanks so much again!

[mjarvis]

Make sure your newState function's parameter matches the type you're selecting in $0.select

extension ViewController: StoreSubscriber {
    func newState(state: MySubStateType) {
        // ...
    }
}

[dav92lee]

Hmm.. I currently don't have any substates

enum TopBarState {
    case home
    case search
}

struct AppState: StateType {
    var searchText: String = ""
    var topBar: TopBarState = TopBarState.home
}

func newState(state: AppState) {
  //TODO: is there anyway to get only state.topBar when state.topBar changed and state.searchText when state.searchText has changed?
}

should I create two separate substates for state.topBar and state.searchText to get my intended flow in TODO above?

Thanks again!

[mjarvis]

In your example, searchText and topBar are substates. they're portions of AppState.

If you make AppState conform to Equatable, then you will automatically get updates only when one of those properties changes.

[dav92lee]

Hello again! I created this function in AppState and had it subclass Equatable

    static func ==(lhs: AppState, rhs: AppState) -> Bool {
        return lhs.searchText == rhs.searchText && lhs.topBar == rhs.topBar
    }

however, I am still getting this error: Cannot invoke 'subscribe' with an argument list of type '(TopBarVC, (_) -> _)'

[dav92lee]

I think this issue solves my problem: #318