SwiftUI's custom modal logic: how to present view from parent - swiftui

Question

Coming from UIKit, I'm building my own modal navigation logic in SwiftUI, because I want custom layouts and animations. Here, I want a generic bottom sheet like so:
I have achieved something close with the following code:
enum ModalType: Equatable {
case normal // ...
#ViewBuilder
var screen: some View {
switch self {
case .normal: ModalView()
// ...
}
}
}
struct ContentView: View {
#State var presentedModal: ModalType?
var body: some View {
VStack {
Button("Present modal", action: { presentedModal = .normal }).foregroundColor(.black)
}
.frame(maxWidth: .infinity, maxHeight: .infinity)
.background(.gray)
.modifier(ModalBottomViewModifier(item: $presentedModal) { $0.screen })
}
}
struct ModalView: View {
#Environment(\.dismissModal) private var dismissModal
var body: some View {
VStack {
Button("Close", action: { dismissModal() })
}
.frame(maxWidth: .infinity)
.frame(height: 300)
.background(
RoundedRectangle(cornerRadius: 32)
.fill(.black.opacity(0.5))
.edgesIgnoringSafeArea([.bottom])
)
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
}
}
// MARK: - Modal logic
struct ModalBottomViewModifier<Item:Equatable, V:View>: ViewModifier {
#Binding var item: Item?
#ViewBuilder var view: (Item) -> V
func body(content: Content) -> some View {
ZStack(alignment: .bottom) {
content
if let item = item {
view(item)
.environment(\.dismissModal, { self.item = nil })
.transition(.move(edge: .bottom))
}
}
.animation(.easeOut, value: item)
}
}
private struct ModalDismissKey: EnvironmentKey {
static let defaultValue: () -> Void = {}
}
extension EnvironmentValues {
var dismissModal: () -> Void {
get { self[ModalDismissKey.self] }
set { self[ModalDismissKey.self] = newValue }
}
}
Now I'd like to make this system reusable, so that I don't have to add the ModalBottomViewModifier to all my app screens. For that, I'd like to be able to apply the modifier to the button instead of the screen, just like it's possible with fullScreenCover:
Button("Present modal", action: { isPresented = true }).foregroundColor(.black)
.fullScreenCover(isPresented: $isPresented) { ModalView() }
This is not possible with my current solution, because the modal view will appear next to the button and not fullscreen.
How can I achieve this? Or should I be doing something different?

Answer 1

Here's a simple solution using UIKit:
extension View {
func presentModalView<Content: View, Item: Equatable>(item: Binding<Item?>, #ViewBuilder view: #escaping (Item) -> Content) -> some View {
func present() {
guard let itemy = item.wrappedValue else {return}
DispatchQueue.main.async {
let topMostController = self.topMostController()
let someView = VStack {
Spacer()
view(itemy)
.environment(\.dismissModal, {item.wrappedValue = nil})
}
let viewController = UIHostingController(rootView: someView)
viewController.view?.backgroundColor = .clear
viewController.modalPresentationStyle = .overFullScreen
topMostController.present(viewController, animated: true)
}
}
return self.onChange(of: item.wrappedValue) { value in
if value != nil {
present()
}else {
topMostController().dismiss(animated: true)
}
}.onAppear {
if item.wrappedValue != nil {
present()
}
}
}
func topMostController() -> UIViewController {
var topController: UIViewController = UIApplication.shared.windows.first!.rootViewController!
while (topController.presentedViewController != nil) {
topController = topController.presentedViewController!
}
return topController
}
}
Usage:
struct ContentView: View {
#State var presentedModal: ModalType?
var body: some View {
VStack {
Button("Present modal", action: { presentedModal = .normal }).foregroundColor(.black)
.presentModalView(item: $presentedModal, view: {$0.screen})
}
.frame(maxWidth: .infinity, maxHeight: .infinity)
.background(.gray)
}
}