Скачать или смотреть How to Detect Paging Completion in UICollectionView with Swift

Learn how to determine when paging is completed in a UICollectionView using Swift, specifically when working with vertical scrolling and full-cell visibility.
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This video is based on the question https://stackoverflow.com/q/62549413/ asked by the user 'Lance Samaria' ( https://stackoverflow.com/u/4833705/ ) and on the answer https://stackoverflow.com/a/62551469/ provided by the user 'Gulfam Khan' ( https://stackoverflow.com/u/8421496/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding Paging Completion in UICollectionView

Implementing paging in a UICollectionView can enhance user experience by ensuring cells are fully viewed one at a time. However, a common challenge developers face is determining when a user has finished swiping, especially when using collectionView.isPagingEnabled = true. This guide aims to provide a clear and concise solution to this problem.

The Problem

When you set up a vertical UICollectionView where each cell is the same size as the collectionView, the goal is to detect when the entire cell is currently displayed on the screen. You want to avoid situations where your code executes while the user is still dragging between cells. For example:

If the user drags from cell 2 to cell 3 and then back to cell 2, you only want to acknowledge the visibility of cell 3 once it's fully on screen, not halfway through the transition.

Here’s the initial code you might be using:

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

The issue arises because this method may still report cells that are only partially on screen, leading to unexpected behaviors in your app.

The Solution

To properly detect when the paging has completed and a cell is fully visible, you can utilize the scrollViewWillEndDragging method. Here’s how to implement this approach:

Step-by-Step Implementation

Override the Delegate Method: Use the scrollViewWillEndDragging method to determine the index of the cell that is about to be fully displayed based on the target content offset.

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

Explanation of the Code

Get the Target Offset: The targetContentOffset indicates where the scrollView will land after the drag ends. By accessing the pointee.y property, you can determine the vertical position of that offset.

Calculate the Current Item: By dividing the target offset's y position by the height of the collectionView, you can derive the index of the item that is currently being shown. This index corresponds to the cell that will fully appear on the screen after scrolling.

Benefits of This Method

Accurate Detection: This solution ensures that you only capture the index of a cell when it's fully displayed, eliminating false positives from intermediate dragging states.

User Experience: By accurately reflecting the current item being viewed, you can enhance responsiveness and functionality in your app based on user interactions.

Conclusion

Understanding when paging is completed in a UICollectionView is crucial for developing smooth and intuitive navigation in your apps. By utilizing the scrollViewWillEndDragging method, you can effectively determine the exact moment a cell comes into full view, providing a more seamless experience for your users.

Feel free to integrate this solution into your project and observe the improved behavior. Happy coding!