SwiftUI Animation Observer

Track SwiftUI animation progress and completion via callbacks! For an animated value (offset, opacity, etc.), get its current value as the animation progresses and then get notified when the animation is completed.



This component is distributed as a Swift package. Just add this repo’s URL to XCode:


How to use

Add the animationObserver modifier to your view. Pass the property whose value is changed by the animation and two optional callbacks:

  1. onProgress is called on each animation frame and reports the current value of the animated property.
  2. onComplete is called when the animation is completed.

struct AnimationObserverTest: View {
  @State private var offset = 0.0
  @State private var offsetSpan: ClosedRange<Double> = 0...1
  @State private var progressPercentage = 0.0
  @State private var isDone = false

   var body: some View {
     GeometryReader { geo in
       VStack {
         Text("Loading: \(progressPercentage)%")
           .frame(height: 50)
           .offset(x: offset)
           .animationObserver(for: offset) { progress in // HERE
             progressPercentage = 100 * abs(progress - offsetSpan.lowerBound) / (offsetSpan.upperBound - offsetSpan.lowerBound)
           } onComplete: {
             isDone = true

         if isDone {
         } else if progressPercentage >= 50 {
           Text("Woooooah, we're half way there...")
         Button("Reload") {
           isDone = false
           offset = -geo.size.width
           offsetSpan = offset...0
           withAnimation(.easeIn(duration: 5)) {
             offset = 0


Check out this recipe for in-depth description of the component and its code. Check out SwiftUIRecipes.com for more SwiftUI recipes!


  • 1.0.0 – Initial release.


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