SwiftUI view parameter does not update as expected-CodePudding

I am curious why this .fullScreenCover display of a view does not update properly with a passed-in parameter unless the parameter is using the @Binding property wrapper. Is this a bug or intended behavior? Is this the fact that the view shown by the fullScreenCover is not lazily generated?

import SwiftUI

struct ContentView: View {
    @State private var showFullScreen = false
    @State private var message = "Initial Message"
    var body: some View {
        VStack {
            Button {
                self.message = "new message"
                showFullScreen = true
            } label: {
                Text("Show Full Screen")
            }

        }.fullScreenCover(isPresented: $showFullScreen) {
            TestView(text: message)
        }
    }
}

struct TestView: View {
    var text: String
    var body: some View {
       Text(text)
    }
}

CodePudding user response：

There is a different fullScreenCover for passing in dynamic data, e.g.

import SwiftUI

struct CoverData: Identifiable {
    var id: String {
        return message
    }
    let message: String
}

struct FullScreenCoverTestView: View {
    @State private var coverData: CoverData?
    
    var body: some View {
        VStack {
            Button {
                coverData = CoverData(message: "new message")
            } label: {
                Text("Show Full Screen")
            }

        }
        .fullScreenCover(item: $coverData, onDismiss: didDismiss) { item in
            TestView(text: item.message)
            .onTapGesture {
                coverData = nil
            }
        }
    }

    func didDismiss() {
        // Handle the dismissing action.
    }

}

struct TestView: View {
    let text: String
    
    var body: some View {
       Text(text)
    }
}

More info and an example in the docs:

https://developer.apple.com/documentation/SwiftUI/AnyView/fullScreenCover(item:onDismiss:content:)