Animations and transitions are decisively one of SwiftUI’s fortes. The framework allows us to go as deep as we want in handling specifics like timing function and duration parameters. Moreover it gives us sophisticated tools like the Animatable protocol to completely customize behavior. Here we are going to rely on the more constricted AnimatableModifier protocol to show how we can manually pause and resume and animation as well as adding the ability to reverse and loop over.

Whenever a SwiftUI animation is triggered, its state is updated immediately regardless of the duration. The Animation struct does not provide us with any sort of callback to indicate whether it has completed. So how can we detect when our views have stopped animating?