SwiftUI TextField resets value and ignores binding

Question

Using a TextField on a mac app, when I hit 'return' it resets to its original value, even if the underlying binding value is changed.

import SwiftUI

class ViewModel {
    let defaultS = "Default String"
    var s = ""
    
    var sBinding: Binding<String> {
        .init(get: {
            print("Getting binding \(self.s)")
            return self.s.count > 0 ? self.s : self.defaultS
        }, set: {
            print("Setting binding")
            self.s = $0
        })
    }
    
}

struct ContentView: View {
    @State private var vm = ViewModel()
    
    var body: some View {
        TextField("S:", text: vm.sBinding)
            .padding()
    }
}

Why is this? Shouldn't it 'get' the binding value and use that? (i.e. shouldn't I see my print statement "Getting binding" in the console after I hit 'return' on the textfield?).

For a cleaner code, I think you should subclass ViewModel with ObservableObject and add @Published var s = "Default String". In The view replace State with StateObject and you should be good to go! — SwiftyJoeyy
– SwiftyJoeyy, Commented Sep 22, 2021 at 14:16
@NoeOnJupiter you're right, that works! If you want to edit the code, I'll accept your answer; otherwise I'll do it later today. Thank you. — aciniglio
– aciniglio, Commented Sep 22, 2021 at 14:27
You cannot use @State for shared values (i.e. sharing it with a ViewModel). If you want to use a ViewModel (or "DataModel" or "Model"), you have to use either a @StateObject or an @ObservedObject. Think of @State as a private variable. — CouchDeveloper
– CouchDeveloper, Commented Sep 22, 2021 at 14:27
You may get some inconsistent results the way you declared the @State now @StateObject. By declaring it as '@StateObject private var vm = ViewModel()` you create a NEW ViewModel and do not share one model. This is fine if you only have one view using it, but if you have multiple different views, you are not using a single source of truth for them. — Yrb
– Yrb, Commented Sep 22, 2021 at 14:56

SwiftyJoeyy · Accepted Answer · 2021-09-22 21:42:45Z

4

Here you go!

class ViewModel: ObservableObject {
    @Published var s = "Default String"
}

struct ContentView: View {
    @StateObject private var vm = ViewModel()
    var body: some View {
        TextField("S:", text: $vm.s)
            .padding()
    }
}

For use in multiple views, in every view where you'd like to use the model add:

@EnvironmentObject private var vm: ViewModel

But don't forget to inject the model to the main view:

ContentView().environmentObject(ViewModel())

edited Sep 22, 2021 at 21:42

answered Sep 22, 2021 at 21:36

SwiftyJoeyy

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