Is there a way to have a global variable between a SwiftUI view and classes indirectly related to it?

Question

I am working on a MacOS Swift project (with SwiftUI), and I am having trouble with updating a text label as an event happens.

struct ContentView: View {
    @State var now = globalString.stringy
    var body: some View {
        VStack {
            Text(now)
            .frame(maxWidth: .infinity, maxHeight: .infinity)
        }.onAppear {
             k.start()

        }

    }

}

struct globalString {
    static var stringy = ""
    static var temperature = 0.0
}

The variable now above refers a global variable in a struct that is being changed while the program is running (in a different class that is not referred to in this code), but the changes to the variable will not show up in the text label.

How can I make a variable that is shared between this view and that class, while still having my view update when there is a change in the variable? The changes made to the variable are in a separate file.

I tried using an observable object and an environment object but neither seemed to work.

If anyone could help, I would greatly appreciate it. Thanks!

Answer 1

To make changes in a SwiftUI view below iOS 17, as it is a static element because of its struct declaration, your object GlobalString must conform to a StateObject to be able to make changes in real-time to a view, and its variables must conform to @Published.

As for SwiftUI view for iOS 17+, you can use the @Observable macro and declare your object as a @State value only.

iOS 17-

class GlobalString: ObservableObject {
  @Published var stringy = ""
  @Published var temperature = 0.0
}

struct ContentView: View {

  @StateObject var globalString = GlobalString()

  var body: some View {
    VStack {
      Text(globalString.stringy)
        .frame(maxWidth: .infinity, maxHeight: .infinity)
    }
    .onAppear { k.start() }
  }
}

iOS 17+

import Observation

@Observable class GlobalString {
  var stringy = ""
  var temperature = 0.0
}

struct ContentView: View {

  @State var globalString = GlobalString()

  var body: some View {
    VStack {
      Text(globalString.stringy)
        .frame(maxWidth: .infinity, maxHeight: .infinity)
    }
    .onAppear { k.start() }
  }
}