Pass variable from UIViewController to SwiftUI View

Question

I can't find a way or a good tutorial to explain how to pass the value of a variable (String or Int) that is owned by a UIViewController to a SwiftUI view that is calling the view.

For example:

class ViewController: UIViewController {
    var myString : String = "" // variable of interest
    ....
    
    func methodThatChangeValueOfString(){
        myString = someValue
    }
}

// to make the view callable on SwiftUI
extension ViewController: UIViewControllerRepresentable {
    typealias UIViewControllerType = ViewController
    
    public func makeUIViewController(context: UIViewControllerRepresentableContext<ViewController>) -> ViewController {
        return ViewController()
    }
    
    func updateUIViewController(_ uiViewController: ViewController, context: UIViewControllerRepresentableContext<ViewController>) {
        
    }
    
}

In SwiftUI I'll have

struct ContentView: View {
    var body: some View {
        ViewController()
    }
}

How can I take myString of the ViewController and use it in ContentView? Thanks in advance

There are several approaches, but it is not very clear the goal. — Asperi
– Asperi, Commented Oct 17, 2020 at 14:52
Ok, I'll explain my specific problem. In the ViewController I have the camera and with Vision I make object detection. The name of the object detected by the camera is saved in a variable as a String. I want to print the string on screen using SwiftUI but I can't pass the data to my SwiftUI View. — Omar El Malak
– Omar El Malak, Commented Oct 17, 2020 at 14:56

lorem ipsum · Accepted Answer · 2021-09-20 12:26:47Z

Use MVVM pattern it is what is recommended with SwiftUI.

Share a ViewModel between your SwiftUI View and your UIKit ViewController.

I suggest you start with the basic Apple SwiftUI tutorials. Specifically how to "Interface with UIKit"

https://developer.apple.com/tutorials/swiftui/interfacing-with-uikit

import SwiftUI

struct SwiftUIView: View {
    @StateObject var sharedVM: SharedViewModel = SharedViewModel()
    var body: some View {
        VStack{
            UIKitViewController_UI(sharedVM: sharedVM)
            Text(sharedVM.myString)
        }
    }
}

class SharedViewModel: ObservableObject{
    @Published var myString = "init String"
}
//Not an extension
struct UIKitViewController_UI: UIViewControllerRepresentable {
    typealias UIViewControllerType = UIKitViewController
    var sharedVM: SharedViewModel
    
    func makeUIViewController(context: Context) -> UIKitViewController {
        return UIKitViewController(vm: sharedVM)
    }
    
    
    func updateUIViewController(_ uiViewController: UIKitViewController, context: Context) {
        
    }
    
}
class UIKitViewController: UIViewController {
    let sharedVM: SharedViewModel
    
    var runCount = 0
    
    init(vm: SharedViewModel) {
        self.sharedVM = vm
        super.init(nibName: nil, bundle: nil)
        //Sample update mimics the work of a Delegate or IBAction, etc
        Timer.scheduledTimer(withTimeInterval: 1.0, repeats: true) { timer in
            self.runCount += 1
            self.methodThatChangeValueOfString()
            if self.runCount == 10 {
                timer.invalidate()
            }
        }
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    func methodThatChangeValueOfString(){
        sharedVM.myString = "method change" + runCount.description
    }
}

struct SwiftUIView_Previews: PreviewProvider {
    static var previews: some View {
        SwiftUIView()
    }
}

Is there a way to create the UIKitViewController_UI in the View struct as a variable and then pass on the sharedVM? I need to call some functions in the UIKitViewController_UI from within the view. However, it calls an 'self' used before all stored properties are initialized error when I try to do this.
@Björn You could create it, but it likely wouldn’t work properly because it would be in a class SwiftUI Views should stay in struct. Ask a question and people can look at your Minimal Reproducible Example but it sounds like you are just setting the variable too soon.

Collectives™ on Stack Overflow

Pass variable from UIViewController to SwiftUI View

1 Answer 1

2 Comments

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Linked

Related