SwiftUI: Custom Modal Animation - animation

Question

I made a custom modal using SwiftUI. It works fine, but the animation is wonky.
When played in slow motion, you can see that the ModalContent's background disappears immediately after triggering ModalOverlay's tap action. However, ModalContent's Text views stay visible the entire time.
Can anyone tell me how I can prevent ModalContent's background from prematurely disappearing?
Slow-mo video and code below:
import SwiftUI
struct ContentView: View {
#State private var isShowingModal = false
var body: some View {
GeometryReader { geometry in
ZStack {
Button(
action: { withAnimation { self.isShowingModal = true } },
label: { Text("Show Modal") }
)
ZStack {
if self.isShowingModal {
ModalOverlay(tapAction: { withAnimation { self.isShowingModal = false } })
ModalContent().transition(.move(edge: .bottom))
}
}.edgesIgnoringSafeArea(.all)
}
}
}
}
struct ModalOverlay: View {
var color = Color.black.opacity(0.4)
var tapAction: (() -> Void)? = nil
var body: some View {
color.onTapGesture { self.tapAction?() }
}
}
struct ModalContent: View {
var body: some View {
GeometryReader { geometry in
VStack {
Spacer()
VStack(spacing: 16) {
Text("Item 1")
Text("Item 2")
Text("Item 3")
}
.frame(width: geometry.size.width)
.padding(.top, 16)
.padding(.bottom, geometry.safeAreaInsets.bottom)
.background(Color.white)
}
}
}
}

Answer 1

The solution (thanks to #JWK):
It's probably a bug. It seems that, during the transition animation (when the views are disappearing) the zIndex of the two views involved (the ModalContent and the ModalOverlay) is not respected. The ModalContent (that is supposed to be in front of the ModalOverlay) is actually moved under the ModalOverlay at the beginning of the animation. To fix this we can manually set the zIndex to, for example, 1 on the ModalContent view.
struct ContentView: View {
#State private var isShowingModal = false
var body: some View {
GeometryReader { geometry in
ZStack {
Button(
action: { withAnimation { self.isShowingModal = true } },
label: { Text("Show Modal") }
)
ZStack {
if self.isShowingModal {
ModalOverlay(tapAction: { withAnimation(.easeOut(duration: 5)) { self.isShowingModal = false } })
ModalContent()
.transition(.move(edge: .bottom))
.zIndex(1)
}
}.edgesIgnoringSafeArea(.all)
}
}
}
}
The investigation that brings to a solution
Transition animations in SwiftUI have still some issues. I think this is a bug. I'm quite sure because:
1) Have you tried to change the background color of your ModalContent from white to green?
struct ModalContent: View {
var body: some View {
GeometryReader { geometry in
VStack {
Spacer()
VStack(spacing: 16) {
Text("Item 1")
Text("Item 2")
Text("Item 3")
}
.frame(width: geometry.size.width)
.padding(.top, 16)
.padding(.bottom, geometry.safeAreaInsets.bottom)
.background(Color.green)
}
}
}
}
This way it works (see the following GIF):
2) Another way to make the bug occur is to change the background color of your ContentView to, for example, green, leaving the ModalContent to white:
struct ContentView: View {
#State private var isShowingModal = false
var body: some View {
GeometryReader { geometry in
ZStack {
Button(
action: { withAnimation(.easeOut(duration: 5)) { self.isShowingModal = true } },
label: { Text("Show Modal") }
)
ZStack {
if self.isShowingModal {
ModalOverlay(tapAction: { withAnimation(.easeOut(duration: 5)) { self.isShowingModal = false } })
ModalContent().transition(.move(edge: .bottom))
}
}
}
}
.background(Color.green)
.edgesIgnoringSafeArea(.all)
}
}
struct ModalOverlay: View {
var color = Color.black.opacity(0.4)
var tapAction: (() -> Void)? = nil
var body: some View {
color.onTapGesture { self.tapAction?() }
}
}
struct ModalContent: View {
var body: some View {
GeometryReader { geometry in
VStack {
Spacer()
VStack(spacing: 16) {
Text("Item 1")
Text("Item 2")
Text("Item 3")
}
.frame(width: geometry.size.width)
.padding(.top, 16)
.padding(.bottom, geometry.safeAreaInsets.bottom)
.background(Color.white)
}
}
}
}
Even in this case it works as expected:
3) But if you change your ModalContent background color to green (so you have both the ContentView and the ModalContent green), the problem occurs again (I won't post another GIF but you can easily try it yourself).
4) Yet another example: if you change the appearance of you iPhone to Dark Appearance (the new feature of iOS 13) your ContentView will automatically become black and, since your ModalView is white, the problem won't occur and everything goes fine.