[Fix] Custom sheet auto dismiss

[CalebRas]

Description

This PR implements fixes to the following bugs that would occur when using the custom sheet modifier in the sample viewer:

1. If there was more than one custom sheet within a given view, some of the sheets would auto-dismiss upon opening, e.g. a sample containing settings sheet would cause the info sheet to auto-dismiss when opened.
2. Whenever a custom sheet was closed, Modifying state during view update, this will cause undefined behavior. would be thrown.
3. Custom sheets dismissed using the DismissAction from the Environment wouldn't always re-present.

URL to custom sheet modifier file: View+Sheet.swift

Linked Issue(s)

• swift/issues/4778

How To Test

Test Code

struct DisplayMapView: View {
    /// A map with imagery basemap.
    @State private var map = Map(basemapStyle: .arcGISImagery)
    
    @State private var isShowingDoneSheet = false
    
    @State private var isShowingDragSheet = false
    
    @State private var isShowingDismissSheet = false
    
    var body: some View {
        // Creates a map view to display the map.
        MapView(map: map)
            .toolbar {
                ToolbarItemGroup(placement: .bottomBar) {
                    Button("Plain") {
                        isShowingDragSheet = true
                    }
                    .sheet(isPresented: $isShowingDragSheet, detents: [.medium, .large], dragIndicatorVisibility: .visible) {
                        print("Dismissed")
                    } content: {
                        Text("Some text.")
                    }
                    Spacer()
                    
                    Button("Done") {
                        isShowingDoneSheet = true
                    }
                    .sheet(isPresented: $isShowingDoneSheet, detents: [.medium]) {
                        print("Dismissed")
                    } content: {
                        NavigationView {
                            Text("Press Done.")
                                .toolbar {
                                    ToolbarItem(placement: .confirmationAction) {
                                        Button("Done") {
                                            isShowingDoneSheet = false
                                        }
                                    }
                                }
                        }
                    }
                    Spacer()
                    
                    Button("Dismiss") {
                        isShowingDismissSheet = true
                    }
                    .sheet(isPresented: $isShowingDismissSheet, detents: [.large]) {
                        print("Dismissed")
                    } content: {
                        DismissSheetView()
                    }
                }
            }
    }
}

private extension DisplayMapView {
    struct DismissSheetView: View {
        /// The action to dismiss the sheet.
        @Environment(\.dismiss) private var dismiss
        
        var body: some View {
            NavigationView {
                Text("Press dismiss")
                    .toolbar {
                        ToolbarItem(placement: .confirmationAction) {
                            Button("Dismiss") {
                                dismiss()
                            }
                        }
                    }
            }
        }
    }
}

• Copy the code above into the Display map sample.
• In the sample, verify the sheets open and close as expected using the buttons in the bottom toolbar.
• Verify that info sheet (top-right button) works as expected.
• Verify the rest of the samples using the custom sheet work as expected.

[yo1995]

Overall looks good! I'll spend a bit more time to take a closer look.

[njarecha]

This is just initial review. I'll continue on testing the fix.

[njarecha]

Changes looks good and improves for some use cases. We can continue looking for improving some other cases separately.

[yo1995]

I've run test on multiple iOS 15 to 17 iPhones and iPads. The change mitigates the sheet dismissal problem. Though there are still some minor bugs, I think it is good to get this in for now.

[CalebRas]

Thank you everyone!