WWDC23 SALE: Save 50% on all my Swift books and bundles! >>

How to combine AnimatableModifier and matchedGeometryEffect?

Forums > SwiftUI

I am trying to combine two of the tutorials that are offered here on this site:

The first one explains how text sizes can be animated: https://www.hackingwithswift.com/quick-start/swiftui/how-to-animate-the-size-of-text

The second one explains how to syncronize animations betweens Views: https://www.hackingwithswift.com/quick-start/swiftui/how-to-synchronize-animations-from-one-view-to-another-with-matchedgeometryeffect

They both work perfectly independent of each other (as expected 😀), but when I try to combine the two to move and resize a Text from one View to another, it doesn't seem to work. I pass in the matchedGeometryEffect's NameSpace.ID to each View and everything then works fine with Circles and Rectangles, but not with Text. Of course, animating Text in itself requires an AnimatableModifier as described in the first link above. While that works ok in itself, it doesn't seem to work in combination with synchronized animations between Views (second link).

Here is some code that demonstrates the problem:

struct ContentView: View {
    @Namespace private var animation
    @State private var isLarge = false

    var body: some View {
        VStack {
            Text("Text that animates correctly")
                .offset(y: isLarge ? -100 : 0)
                .modifier(AnimatingFontSize(fontSize: isLarge ? 28 : 16))

            Button("Toggle") {
                withAnimation(.easeInOut(duration: 5.0)) {
            .padding(.vertical, 20)

            if isLarge {
                ViewWithText(animation: animation, color: .green, fontSize: 28, yOffset: 100)
            } else {
                ViewWithText(animation: animation, color: .red, fontSize: 16, yOffset: 0)

struct ViewWithText: View {
    var animation: Namespace.ID
    var color: Color
    var fontSize: CGFloat
    var yOffset: CGFloat

    var body: some View {
        VStack {
                .matchedGeometryEffect(id: "Circle", in: animation)
                .frame(width: 50 + yOffset / 2, height: 50 + yOffset / 2)

            Text("Embedded Text")
                .matchedGeometryEffect(id: "Text", in: animation)
                .offset(y: yOffset)
                .modifier(AnimatingFontSize(fontSize: fontSize))

struct AnimatingFontSize: AnimatableModifier {
    var fontSize: CGFloat

    var animatableData: CGFloat {
        get { fontSize }
        set { fontSize = newValue }

    func body(content: Self.Content) -> some View {
            .font(.system(size: fontSize))

The [Toggle] button toggles between large and small Texts and red and green Circles. The "Text that animates correctly" shows that the animatable font modifier works correctly. The ViewWithText contains a Circle and a Text. The Circles show that matchedGeometryEffect works correctly.

Alas, the "Embedded Text" in ViewWithText does not animate correctly: it fades in and out as if it were the default animation. I slowed down the animation so you can clearly see what happens. The AnimatingFontSize modfier does not seem to have any effect here.

Any ideas?

Thanks in advance!


Save 50% in my WWDC23 sale.

SAVE 50% To celebrate WWDC23, all our books and bundles are half price, so you can take your Swift knowledge further without spending big! Get the Swift Power Pack to build your iOS career faster, get the Swift Platform Pack to builds apps for macOS, watchOS, and beyond, or get the Swift Plus Pack to learn advanced design patterns, testing skills, and more.

Save 50% on all our books and bundles!

Archived topic

This topic has been closed due to inactivity, so you can't reply. Please create a new topic if you need to.

All interactions here are governed by our code of conduct.

Unknown user

You are not logged in

Log in or create account

Link copied to your pasteboard.