why does SwiftUI not update the values in nested ForEach Loop?

Question

i have this code. it is pretty simple. i change the rows by one when tapping the button.

but only the output in the line "works" works, the other one always is 0.

What am i doing wrong!?

you can copy and paste the code to reproduce the error.

class GlobalData : ObservableObject {

    @Published var rows : Int = 0
}


struct ContentView: View {

    @ObservedObject var globalData = GlobalData()

    var body: some View {
        VStack {
            Text("\(self.globalData.rows)") // works...
            ForEach (0..<4) { y in
                HStack () {
                    ForEach (0..<3) { x in

                        ForEach (0..<3) { index -> Text in
                            Text("\(self.globalData.rows)") // shows always 0
                        }
                    }
                }
            }
            Button(action: {
                self.globalData.rows = self.globalData.rows + 1
            }) {
                Text("Increase rows")
            }
        }
    }
}

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

Answer 1

The reason is in constant ForEach(range). If supposed anything changed inside ForEach use dynamic data sequence.

Here is a solution for your case. Tested with Xcode 11.4 / iOS 13.4.

struct ContentView: View {

    @ObservedObject var globalData = GlobalData()

    var body: some View {
        VStack {
            Text("\(self.globalData.rows)") // works...
            ForEach (Array(0...3), id: \.self) { y in
                HStack () {
                    ForEach (Array(0...2), id: \.self) { x in

                        ForEach (Array(0...2), id: \.self) { index -> Text in
                            Text("\(self.globalData.rows)") // works ...
                        }
                    }
                }
            }
            Button(action: {
                self.globalData.rows = self.globalData.rows + 1
            }) {
                Text("Increase rows")
            }
        }
    }
}