How to make custom .sheet viewmodifier - swiftui

Question

I am trying to recreate the native .sheet() view modifier in SwiftUI. When I look at the definition, I get below function, but I'm not sure where to go from there.
The .sheet somehow passes a view WITH bindings to a distant parent at the top of the view-tree, but I can't see how that is done. If you use PreferenceKey with an AnyView, you can't have bindings.
My usecase is that I want to define a sheet in a subview, but I want to activate it at a distant parent-view to avoid it interfering with other code.
func showSheet<Content>(isPresented: Binding<Bool>, onDismiss: (() -> Void)? = nil, #ViewBuilder content: #escaping () -> Content) -> some View where Content : View {
// What do I put here?
}

Answer 1

So, I ended up doing my own sheet in SwiftUI using a preferenceKey for passing the view up the view-tree, and an environmentObject for passing the binding for showing/hiding the sheet back down again.
It's a bit long-winded, but here's the gist of it:
struct HomeOverlays<Content: View>: View {
#Binding var showSheet:Bool
#State private var sheet:EquatableViewContainer = EquatableViewContainer(id: "original", view: AnyView(Text("No view")))
#State private var animatedSheet:Bool = false
#State private var dragPercentage:Double = 0 /// 1 = fully visible, 0 = fully hidden
// Content
let content: Content
init(_ showSheet: Binding<Bool>, #ViewBuilder content: #escaping () -> Content) {
self._showSheet = showSheet
self.content = content()
}
var body: some View {
GeometryReader { geometry in
ZStack {
content
.blur(radius: 5 * dragPercentage)
.opacity(1 - dragPercentage * 0.5)
.disabled(showSheet)
.scaleEffect(1 - 0.1 * dragPercentage)
.frame(width: geometry.size.width, height: geometry.size.height)
if animatedSheet {
sheet.view
.background(Color.greyB.opacity(0.5).edgesIgnoringSafeArea(.bottom))
.cornerRadius(5)
.transition(.move(edge: .bottom).combined(with: .opacity))
.dragToSnap(snapPercentage: 0.3, dragPercentage: $dragPercentage) { showSheet = false } /// Custom modifier for measuring how far the view is dragged down. If more than 30% it snaps showSheet to false, and otherwise it snaps it back up again
.edgesIgnoringSafeArea(.bottom)
}
}
.onPreferenceChange(HomeOverlaySheet.self, perform: { value in self.sheet = value } )
.onChange(of: showSheet) { show in sheetUpdate(show) }
}
}
func sheetUpdate(_ show:Bool) {
withAnimation(.easeOut(duration: 0.2)) {
self.animatedSheet = show
if show { dragPercentage = 1 } else { dragPercentage = 0 }
}
// Delay onDismiss action if removing sheet, so animation can complete
if show == false {
DispatchQueue.main.asyncAfter(deadline: .now() + 0.3) {
sheet.action()
}
}
}
}
struct HomeOverlays_Previews: PreviewProvider {
static var previews: some View {
HomeOverlays(.constant(false)) {
Text("Home overlays")
}
}
}
// MARK: Preference key for passing view up the tree
struct HomeOverlaySheet: PreferenceKey {
static var defaultValue: EquatableViewContainer = EquatableViewContainer(id: "default", view: AnyView(EmptyView()) )
static func reduce(value: inout EquatableViewContainer, nextValue: () -> EquatableViewContainer) {
if value != nextValue() && nextValue().id != "default" {
value = nextValue()
}
}
}
// MARK: View extension for defining view somewhere in view tree
extension View {
// Change only leading view
func homeSheet<SheetView: View>(onDismiss action: #escaping () -> Void, #ViewBuilder sheet: #escaping () -> SheetView) -> some View {
let sheet = sheet()
return
self
.preference(key: HomeOverlaySheet.self, value: EquatableViewContainer(view: AnyView( sheet ), action: action ))
}
}