菜单未更新（SwiftUI 错误？）

Question

I'm using macOS Montery Beta 4 along with Xcode 13 Beta 4, and I think I've discovered a bug in SwiftUI .

When using a CommandGroup along with a button that is enabled/disabled based on a condition, the CommandGroup doesn't update. CommandMenu does however.

Reproduction:

1. Create a new SwiftUI macOS project
2. Paste the following code in the App file:

class Test: ObservableObject {
    @Published var num = 0
}

@main
struct TestApp: App {
    @StateObject private var test = Test()
    var body: some Scene {
        WindowGroup {
            ContentView()
                .environmentObject(test)
        }
        .commands {
            CommandGroup(after: .newItem) {
                Button(action: {}) {
                    Text("Test menu item")
                }
                .disabled(test.num == 0)
            }
        }
    }
}

3. Paste the following code in the ContentView file:

struct ContentView: View {
    @EnvironmentObject var test: Test
    
    var body: some View {
        Button(action: {
            test.num += 1
        }) {
            Text(String(test.num) + " ---------")
        }
    }
}

4. Run the app, and click on the File menu. You should see that "Test menu item" is disabled as expected.
5. Click on the button. This simply increments a number by 1. However, "Test menu item" is still disabled, even though test.num != 0.

The thing is, replacing the CommandGroup with CommandMenu("Test menu") fixes it.

All the app does is have a menu item that is disabled if a number is zero. Pressing the button makes that number not zero, but the menu item stays disabled.

Is anybody able to reproduce this, and is this a bug on my part?

Answer 1

a minor variation of @George_E answer, is this:

 CommandGroup(after: .newItem) {
       TestView(test: test)
 }
 
 struct TestView: View {
     @ObservedObject var test: Test
  
     var body: some View {
         Button(action: {}) {
             Text("Test menu item")
         }
         .disabled(test.num == 0)
     }
 }

Answer 2

I wouldn't expect that to be intended behaviour. However, I have found a workaround to fix this.

It's odd that onChange(of:perform:) isn't run when test.num changes, but we can still detect the publisher. So I split this into a separate view and when the view receives a new value, the button is updated.

Code:

CommandGroup(after: .newItem) {
    TestView(pub: test.$num)
}

struct TestView: View {
    let pub: Published<Int>.Publisher
    @State private var disabled = true

    var body: some View {
        Button(action: {}) {
            Text("Test menu item")
        }
        .disabled(disabled)
        .onReceive(pub) { new in
            disabled = new == 0
        }
    }
}