How do I go about dynamically changing the UITableViewCell
height? I've tried implementing the following, but for some reason, it isn't working. The code crashes as soon as I load the view controller displaying this table view
func tableView(_ tableView: UITableView, heightForRowAt indexPath: IndexPath) -> CGFloat {
let cell = tableView.cellForRow(at: indexPath) as! AvailableRideCell
return cell.getHeight()
}
This is the getHeight
function in my AvailableRideCell
func getHeight() -> CGFloat {
return self.destinationLabel.optimalHeight + 8 + self.originLabel.optimalHeight + 8 + self.priceLabel.optimalHeight
}
And this is the optimalHeight
function
extension UILabel {
var optimalHeight : CGFloat {
get {
let label = UILabel(frame: CGRect(x: 0, y: 0, width: self.bounds.width, height: CGFloat.greatestFiniteMagnitude))
label.numberOfLines = 0
label.lineBreakMode = NSLineBreakMode.byWordWrapping
label.font = self.font
label.text = self.text
label.sizeToFit()
return label.frame.height
}
}
}
You code crashes because of this line
let cell = tableView.cellForRow(at: indexPath) as! AvailableRideCell
From Apple Documentation we know that this method is used for optimization. The whole idea is to get cells heights without wasting time to create the cells itself. So this method called before initializing any cell, and tableView.cellForRow(at: indexPath)
returns nil
. Because there are no any cells yet. But you're making force unwrapping with as! AvailableRideCell
and your code crashed.
So at first, you need to understand, why you should not use any cells inside the cellForRow(at )
method.
After that, you need to change the logic so you could compute content height without calling a cell.
For example, in my projects, I've used this solution
String implementation
extension String {
func height(for width: CGFloat, font: UIFont) -> CGFloat {
let maxSize = CGSize(width: width, height: CGFloat.greatestFiniteMagnitude)
let actualSize = self.boundingRect(with: maxSize,
options: [.usesLineFragmentOrigin],
attributes: [NSAttributedStringKey.font: font],
context: nil)
return actualSize.height
}
}
UILabel implementation
extension String {
func height(for width: CGFloat, font: UIFont) -> CGFloat {
let labelFrame = CGRect(x: 0, y: 0, width: width, height: CGFloat.greatestFiniteMagnitude)
let label = UILabel(frame: labelFrame)
label.numberOfLines = 0
label.lineBreakMode = .byWordWrapping
label.font = font
label.text = self
label.sizeToFit()
return label.frame.height
}
}
With that, all you need to do is to compute your label and store its font.
var titles = ["dog", "cat", "cow"]
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
// number of rows is equal to the count of elements in array
return titles.count
}
func tableView(_ tableView: UITableView, heightForRowAt indexPath: IndexPath) -> CGFloat {
let cellTitle = titles[indexPath.row]
return cellTitle.height(forWidth: labelWidth, font: labelFont)
}
Dynamic rows height changing
If you'll need to update row height, all you need to do is to call this method when your content had been changed. indexPath
is the index path of changed item.
tableView.reloadRows(at: [indexPath], with: .automatic)
Hope it helps you.