How to Get the Visible Cells of a UITableView

UITableView is one of the most frequently used UI components in iOS development, used to display a scrollable list of items in a single column. One common requirement when working with UITableView is to get a list of currently visible cells, which can be used for a variety of purposes, such as updating the visible cells or performing custom animations.

In this article, we'll discuss how to get the visible cells of a UITableView in an efficient and reliable manner.

Understanding the Problem

Before we dive into the solution, let's understand the problem we're trying to solve. A UITableView is designed to efficiently display a large number of cells by only creating and displaying the cells that are currently visible on the screen. As the user scrolls through the table, new cells are created and old cells are recycled to conserve memory.

When we say "visible cells," we're referring to the cells that are currently displayed on the screen, along with any partially visible cells that are currently off-screen but can be seen as the user scrolls. In other words, we want to get a list of all the cells that the user can currently see.

Using UITableView's Visible Cells Property

The simplest way to get the visible cells of a UITableView is to use the visibleCells property, which returns an array of all the cells that are currently visible on the screen. Here's an example:

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1let visibleCells = tableView.visibleCells

This will give us an array of all the cells that are currently visible. However, it's worth noting that this method can be somewhat slow if the table view contains a large number of cells. This is because visibleCells has to iterate over all the cells in the table view, checking which ones are currently visible.

Using UITableView's IndexPath for Visible Rows Property

A faster and more efficient way to get the visible cells is to use the indexPathsForVisibleRows property of the UITableView. This property returns an array of IndexPath objects, which represent the index paths of all the currently visible rows. We can then use these index paths to retrieve the corresponding cells using the cellForRow(at:) method of the UITableView.

Here's an example of how to use this method:

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1if let indexPaths = tableView.indexPathsForVisibleRows {
2    for indexPath in indexPaths {
3        if let cell = tableView.cellForRow(at: indexPath) {
4            // Do something with the cell
5        }
6    }
7}

This method is generally faster than visibleCells because it doesn't require iterating over all the cells in the table view. Instead, it simply returns an array of index paths that represent the currently visible rows. We can then use these index paths to retrieve the corresponding cells directly.

Conclusion

In this article, we've discussed two methods for getting the visible cells of a UITableView. The first method, using the visibleCells property, is simple but can be slow if the table view contains a large number of cells. The second method, using the indexPathsForVisibleRows property, is faster and more efficient, as it only returns an array of index paths for the currently visible rows.

When working with UITableView, it's important to be mindful of memory usage and performance, especially if your table view contains a large number of cells. By using these techniques to get the visible cells, you can ensure that your app remains responsive and efficient, even as the user scrolls through a large table.