ios - SwiftUI withAnimation completion callback

Question

I have a swiftUI animation based on some state:

withAnimation(.linear(duration: 0.1)) {
    self.someState = newState
}

Is there any callback which is triggered when the above animation completes?

If there are any suggestions on how to accomplish an animation with a completion block in SwiftUI which are not withAnimation, I'm open to those as well.

I would like to know when the animation completes so I can do something else, for the purpose of this example, I just want to print to console when the animation completes.

Answer 1

On this blog this Guy Javier describes how to use GeometryEffect in order to have animation feedback, in his example he detects when the animation is at 50% so he can flip the view and make it looks like the view has 2 sides

here is the link to the full article with a lot of explanations: https://swiftui-lab.com/swiftui-animations-part2/

I will copy the relevant snippets here so the answer can still be relevant even if the link is not valid no more:

In this example @Binding var flipped: Bool becomes true when the angle is between 90 and 270 and then false.

struct FlipEffect: GeometryEffect {

    var animatableData: Double {
        get { angle }
        set { angle = newValue }
    }

    @Binding var flipped: Bool
    var angle: Double
    let axis: (x: CGFloat, y: CGFloat)

    func effectValue(size: CGSize) -> ProjectionTransform {

        // We schedule the change to be done after the view has finished drawing,
        // otherwise, we would receive a runtime error, indicating we are changing
        // the state while the view is being drawn.
        DispatchQueue.main.async {
            self.flipped = self.angle >= 90 && self.angle < 270
        }

        let a = CGFloat(Angle(degrees: angle).radians)

        var transform3d = CATransform3DIdentity;
        transform3d.m34 = -1/max(size.width, size.height)

        transform3d = CATransform3DRotate(transform3d, a, axis.x, axis.y, 0)
        transform3d = CATransform3DTranslate(transform3d, -size.width/2.0, -size.height/2.0, 0)

        let affineTransform = ProjectionTransform(CGAffineTransform(translationX: size.width/2.0, y: size.height / 2.0))

        return ProjectionTransform(transform3d).concatenating(affineTransform)
    }
}

You should be able to change the animation to whatever you want to achieve and then get the binding to change the state of the parent once it is done.