22 May 2024 Leave a comment Tech-Help
Auto Layout is an essential tool for iOS developers when creating user interfaces that need to adapt to different screen sizes and orientations. One common challenge is using Auto Layout within UITableViewCells to let each cell’s content and subviews determine the row height dynamically, while maintaining smooth scrolling performance. This article will guide you through the steps to achieve this.
Conceptual Description
The primary goal is to set up your UITableViewCells in a way that their heights can adjust dynamically based on their content. The following steps will help you achieve this.
1. Set Up & Add Constraints
In your UITableViewCell subclass, add constraints so that the subviews of the cell are pinned to the edges of the cell’s contentView. Ensure that the content compression resistance and content hugging constraints in the vertical dimension for each subview are not overridden by higher-priority constraints.
Example:
// In your UITableViewCell subclass
override func updateConstraints() {
if !didSetupConstraints {
// Add constraints here
didSetupConstraints = true
}
super.updateConstraints()
}
2. Determine Unique Table View Cell Reuse Identifiers
For each unique set of constraints in the cell, use a unique cell reuse identifier. Avoid adding cells with completely different sets of constraints to the same reuse pool as this can lead to performance issues.
3. Enable Row Height Estimation
For iOS 8 and later, enable self-sizing table view cells by setting the table view’s rowHeight property to UITableView.automaticDimension and assigning a value to the estimatedRowHeight property.
self.tableView.rowHeight = UITableView.automaticDimension;
self.tableView.estimatedRowHeight = 44.0; // or any average height
4. Do a Layout Pass & Get The Cell Height (for iOS 7 support)
Instantiate an offscreen instance of the table view cell for height calculations. Configure the cell with the exact content it would hold if displayed, force the cell to layout its subviews, and use the systemLayoutSizeFittingSize method to find the required height.
func calculateHeightForConfiguredSizingCell(cell: UITableViewCell) -> CGFloat {
cell.setNeedsLayout()
cell.layoutIfNeeded()
let height = cell.contentView.systemLayoutSizeFittingSize(UILayoutFittingCompressedSize).height + 1.0
return height
}
5. Use Estimated Row Heights
Providing a temporary estimate for row heights of cells that are not yet onscreen helps in maintaining smooth scrolling performance.
6. Add Row Height Caching (if needed)
If performance issues persist, consider implementing caching for cell heights. Let the Auto Layout engine solve the constraints the first time, then cache the calculated height for that cell and use the cached value for future requests.
Practical Example
Here’s a practical example of setting up a UITableView with dynamic cell heights:
override func viewDidLoad() {
super.viewDidLoad()
self.tableView.estimatedRowHeight = 80
self.tableView.rowHeight = UITableView.automaticDimension
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: "cell", for: indexPath) as! MyCustomCell
cell.myLabel.text = self.data[indexPath.row]
return cell
}
Conclusion
By following these steps, you can ensure that your UITableViewCells dynamically adjust their heights based on their content, providing a better user experience. For more detailed information, you can refer to our documentation.
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