UIView.animateKeyFrames Causes UIButton Click Failures: How to Fix Your View Hierarchy Confusion

Discover how to solve UIButton interaction problems when using UIView.animateKeyFrames in your iOS app. Learn about view hierarchy and NSLayoutConstraints with clear examples.
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This video is based on the question https://stackoverflow.com/q/73115179/ asked by the user 'kelsey-debug' ( https://stackoverflow.com/u/16004664/ ) and on the answer https://stackoverflow.com/a/73125181/ provided by the user 'DonMag' ( https://stackoverflow.com/u/6257435/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding UIButton Click Issues with UIView.animateKeyFrames

As iOS developers, we strive to create smooth and interactive user interfaces. However, when it comes to animations, especially using UIView.animateKeyFrames, we sometimes encounter unexpected behavior — particularly with UIButton interactions. In this guide, we’ll explore a common issue where UIButton clicks become unresponsive due to transformations applied during animations and offer a robust solution.

The Problem

In the scenario we've encountered, a custom ToastView is designed to slide up from the bottom of the screen, functioning as a notification bar. The ToastView includes a label, an image, and a dismiss button. While the button works perfectly when the toast is positioned with NSLayoutConstraints, it stops responding once the view is animated upwards. This behavior leads to the frustrating experience where users cannot dismiss or interact with the button, despite it visually appearing on the screen.

Why Does This Happen?

The core issue arises because of how the UIKit manages the view hierarchy and interaction. When the ToastView is animated using transformation (like CGAffineTransform), it shifts its visual representation but does not actually change its frame in the view hierarchy. As a result:

The button remains "physically" below its original position in terms of the layout, even though visually, it appears to be on the screen.

Users cannot tap the button because the touch events are still being calculated based on its original frame.

Solution: Adjusting Layout Constraints Instead of Using Transforms

Instead of using transforms to animate the ToastView, it’s more effective and reliable to adjust the NSLayoutConstraints directly. Here’s how to adjust the animateToast method and implement smooth animations while ensuring user interaction remains intact.

Step-By-Step Solution

Animate with NSLayoutConstraints: Instead of transforming the view, decrease the top constraint value to move the view upwards smoothly.

Ensure Layout Updates: Use layoutIfNeeded() to refresh the layout immediately after changing a constraint.

Asynchronous Animation: Call the animation adjustment on the main thread to ensure UIKit can manage updates properly.

Updated animateToast Method

Here’s how you can modify the animateToast() function in your ToastView class:

[[See Video to Reveal this Text or Code Snippet]]

Key Takeaways

UIView animations should loosely tie to the underlying layout. Using constraints provides a more consistent interaction experience than relying on transformation methods.

Always test the user interactivity post-animation. Make sure the buttons and other UI elements are still respondable after any transformations you apply.

By following these guidelines, you ensure that your ToastView not only animates smoothly but also maintains its interactive capabilities, leading to a better user experience. Happy coding!