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mbrandonw/app-storage.swift

Created April 3, 2024 23:26
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  1. mbrandonw created this gist Apr 3, 2024.
    49 changes: 49 additions & 0 deletions app-storage.swift
    View file
    Original file line number Diff line number Diff line change
    @@ -0,0 +1,49 @@
    /*
    The @AppStorage property wrapper does not fully work unless installed
    directly in a view. In particular, it does not work when used in an
    observable object.

    Paste the following into a fresh project, run it in the simulator,
    and notice that tapping the "Toggle model.isOn" button causes the view
    to update propertly, but tapping the "Toggle UserDefaults directly"
    button does not. This means that writing directly to user defaults
    does cause @AppStorage to update, _unless_ @AppStorage is used in the
    view.
    */

    import SwiftUI

    @main
    struct MainApp: App {
    var body: some Scene {
    WindowGroup {
    FeatureView()
    }
    }
    }

    class FeatureModel: ObservableObject {
    @AppStorage("isOn") var isOn = false
    }

    struct FeatureView: View {
    @ObservedObject var model = FeatureModel()
    var body: some View {
    Form {
    Section {
    Text("model.isOn: \(model.isOn.description)")
    }
    Section {
    Button("Toggle model.isOn") { model.isOn.toggle() }
    Button("Toggle UserDefaults directly") {
    print("model.isOn before", model.isOn)
    UserDefaults.standard.setValue(
    !UserDefaults.standard.bool(forKey: "isOn"),
    forKey: "isOn"
    )
    print("model.isOn after", model.isOn)
    }
    }
    }
    }
    }