Swift Modal transition partial curl on dismiss got stuck

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06-10-2024

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Swift Modal Transition: Unraveling the Partial Curl Dismiss Bug

Presenting content modally in your Swift app often involves a visually appealing transition. A popular choice is the "curl" effect, where the presented view smoothly emerges from the bottom of the screen. However, you might encounter a frustrating bug where the dismissal animation gets stuck in a partial curl state.

The Scenario:

Let's imagine you're working on an iOS app with a modal view controller that presents using a curl transition. You expect the dismissal animation to smoothly curl the view back down, but instead, it gets stuck halfway through the transition, leaving your view in a strange, partially curled state.

Original Code (Simplified):

// Presenting the modal view controller
present(modalViewController, animated: true, completion: nil)

// Dismissing the modal view controller
dismiss(animated: true, completion: nil)

Understanding the Problem:

The partial curl bug usually arises when you try to dismiss the modal view controller before the presentation animation has completely finished. This can occur due to various reasons, such as:

• User interaction: The user might tap outside the modal view or interact with another UI element before the presentation is fully complete.
• Asynchronous operations: If you dismiss the modal view controller based on an asynchronous operation (like a network request or timer), it might happen before the presentation animation has finished.

Debugging and Solutions:

1. Verify Presentation Completion: Ensure that the completion closure of the present method is properly executed before you initiate the dismissal. This helps confirm that the presentation animation has fully completed.

   present(modalViewController, animated: true) {
       // Dismiss logic should be placed here
   }
   

2. Utilize Completion Handlers: For asynchronous operations, use a completion handler within the dismiss method to ensure the dismissal animation happens only after the operation is complete.

   // Dismissing with a completion handler
   dismiss(animated: true) { 
       // Code to execute after dismissal is finished
   }
   

3. Delay Dismissal: If the dismissal is triggered due to user interaction, you can introduce a slight delay before dismissing the modal view controller. This can give the presentation animation time to complete.

   DispatchQueue.main.asyncAfter(deadline: .now() + 0.2) { 
       // Dismiss logic here 
   }
   

4. Customize Transition: For greater control, you can customize the presentation and dismissal transitions using UIViewControllerAnimatedTransitioning protocol. This allows you to manage the animation duration and other properties to avoid the partial curl bug.

Additional Tips:

• Logging: Add logging statements to track the execution flow of your presentation and dismissal logic, which helps pinpoint where the issue originates.
• Debugging tools: Utilize tools like the Xcode debugger and breakpoints to inspect the state of your code and variables during the animation process.

Conclusion:

The partial curl bug can be frustrating, but by understanding its causes and implementing appropriate solutions, you can ensure a smooth and visually appealing modal transition experience for your users. Remember to carefully handle the completion of presentations, consider asynchronous operations, and customize transitions if necessary.