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Learn how to effectively handle animations in SwiftUI so that they continue seamlessly when returning from background state with UIViewRepresentable.
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This video is based on the question https://stackoverflow.com/q/67517009/ asked by the user 'Guillaume' ( https://stackoverflow.com/u/7037428/ ) and on the answer https://stackoverflow.com/a/67517357/ provided by the user 'Raja Kishan' ( https://stackoverflow.com/u/14733292/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Handling Animations in SwiftUI: Resuming After Background State

When developing a SwiftUI application, you may want to implement animations that run continuously. A common challenge developers face is that their animations stop when the app goes into the background and do not resume when the app is reopened. This can be particularly frustrating if you're using UIViewRepresentable for custom views, like in our example of a sonar view. In this guide, we'll explore how to resume animations after returning from the background state in SwiftUI.

The Problem

In our example, we have a sonar view that employs the makeUIView function within TargetView, a struct conforming to UIViewRepresentable. Here's a snippet of the code that illustrates the issue:

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Here’s what happens:

When the app goes into the background, the animation halts.

When the app comes back to the foreground, the animation does not restart automatically.

This entails the need for a more robust solution to ensure the animation continues seamlessly.

The Solution: Using CABasicAnimation

Instead of relying on UIView.animate, we can leverage CABasicAnimation. This method provides more precision and control over animations, particularly when handling background states. Below is the implementation of the revised updateUIView function:

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Key Attributes of CABasicAnimation

keyPath: This defines which property you want to animate. In this case, we are scaling the transform property of the layer.

toValue: This indicates to what value the animation should transition. Here, it's set to 1.2, meaning we want to scale the view to 120% of its original size.

duration: The duration of the animation. We set it to 1.75 seconds.

isRemovedOnCompletion: We set this to false to ensure the animation remains on the layer even when moving to the background.

repeatCount: By setting this to the greatest finite magnitude, the animation will continue indefinitely.

autoreverses: This makes the animation reverse to its original value after reaching its toValue, creating a smooth pulsating effect.

Integration into Your SwiftUI View

You can integrate this TargetView into your SwiftUI structure as follows:

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Include the sonar view in the SwiftUI scene while ensuring the necessary environment and modifiers such as .frame and .opacity are appropriately used.

This integration will ensure that your sonar animation will continue to pulse in the background and resume when your app returns to the foreground, giving users a seamless experience.

Conclusion

By transitioning to CABasicAnimation, you can eliminate the issue of animations stopping when your SwiftUI app goes into the background and ensure that they resume smoothly once your app is back in the foreground. This approach not only enhances user experience but also makes your animations look more professional and polished. Keep exploring the powerful capabilities of SwiftUI and UIKit to create dynamic, engaging apps!