What is the best way to set the duration of an animation in SwiftUI?

[imthath-m]

Here's what we have done now with the .animationSpeed(_:) modifier.

struct PlaybackDurationDemo: View {
  let animation: LottieAnimation? = LottieAnimation.named("check")

  var body: some View {
    LottieView {
      animation
    }
    .animationSpeed(animation!.speedToPlay(forDuration: 10))
    .playing()
  }
}

extension LottieAnimation {
  var timeInterval: TimeInterval {
    (endFrame - startFrame) / framerate
  }

  func speedToPlay(forDuration duration: TimeInterval) -> Double {
    timeInterval / duration
  }
}

Would love to know if this approach is correct or if there is an easier way.

[calda]

Your approach makes sense to me. Alternatively you could create a view modifier in an extension like .duration(10, animation: animation) that under the hood performs the same math and applies the animationSpeed modifier.

[calda]

Another option is to use a .configure { ... } with something like this:

.configure { animationView in
  guard let animation = animationView.animation else { return }
  let expectedSpeed = animation.speedToPlay(forDuration: 10)

  if animationView.animationSpeed != expectedSpeed {
    animationView.animationSpeed = expectedSpeed
  }
}

This could be wrapped up in a custom view modifier like .duration(10) and seems appealing since then you don't have to pass the animation into the view modifier.

[imthath-m]

Thanks for the response and suggestions. Not needing to pass the animation is exactly what we want.

Does it make sense to add it a .duration(_:) modifier to library? I can open a PR if that's acceptable.

[calda]

Since the animation duration is typically defined via the animation json itself, I think we can continue without it for now.