Open Radar

 
Please describe the issue:
If a SwiftUI Stepper has increment/decrement functions _outside of the View_, then the +/-buttons can become disabled unexpectedly

Please list the steps you took to reproduce the issue:
1. Add the attached SwiftUI View to an iOS project
2. Run the app
3. Increment/decrement the first Stepper - note that it consistently works correctly
4. Increment/decrement the second stepper - note that the +/- buttons become disabled after a few clicks

The first stepper uses increment/decrement functions inside the View itself. The second uses functions inside a ViewModel (ie, not the View).

I don’t know why that would cause different behaviour, but I wouldn’t expect the +/- buttons to ever be disabled if the Stepper isn’t bound to a closed range.

What did you expect to happen?
+/- buttons should work, even if it’s using increment/decrement functions outside the View.

What actually happened?
+/- buttons can get disabled if the increment/decrement arguments reference a function outside of the View.



//
//  ContentView.swift
//  SwiftUI-stepper-problem
//

import SwiftUI

class ViewModel: ObservableObject {
    @Published var valueString: String = ""
    
    private var value: Int = 10 {
        didSet {
            self.updateUI()
        }
    }
    
    init() {
        self.updateUI()
    }
    
    private func updateUI() {
        self.valueString = "value: \(self.value)"
    }
    
    func increment() {
        self.value += 1
    }
    
    func decrement() {
        self.value -= 1
    }
}

struct ContentView: View {
    @ObservedObject var viewModel = ViewModel()
    
    var body: some View {
        Form {
            // This first Stepper uses the `increment` and `decrement` functions in the View
            Section(header: Text("Increment/decrement functions in the view. This works well")) {
                Stepper(onIncrement: self.increment,
                        onDecrement: self.decrement) {
                            Text(self.viewModel.valueString)
                }
            }
            
            // This Stepper uses `increment` and `decrement` functions in the ViewModel directly. After a few clicks, the `-` or `+` button is disabled
            Section(header: Text("Increment/decrement functions in the viewmodel. This gets stuck")) {
                Stepper(onIncrement: self.viewModel.increment,
                        onDecrement: self.viewModel.decrement) {
                            Text(self.viewModel.valueString)
                }
            }
        }
    }
    
    func increment() {
        self.viewModel.increment()
    }
    
    func decrement() {
        self.viewModel.decrement()
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}