Kern Attribute cause Performance slow issue in UITextview - ios

Question

I want to set width of each characters when user typing. I use NSAttributeString with key .Kern that works well but when the text length is bigger about 1000+, I touch on screen to place cursor position in front of first line and typing new characters that cause Performance issue, too slow and lag.
// Initialize once and reuse every time
lazy var paragraphStyle: NSMutableParagraphStyle = {
let paragraphStyle = NSMutableParagraphStyle()
paragraphStyle.lineBreakMode = .byWordWrapping
paragraphStyle.alignment = .left
return paragraphStyle
}()
// Initialize once and reuse every time
lazy var alignTextAttributes: [NSAttributedString.Key: Any] = {
return [
.kern : 30,
.paragraphStyle : paragraphStyle,
.foregroundColor : UIColor.black,
]
}()
func textView(_ textView: UITextView, shouldChangeTextIn range: NSRange, replacementText text: String) -> Bool {
// If I want to set each characters with different kern values, how can I do that?
alignTextAttributes[.kern] = textView.text.count.isMultiple(of: 2) ? 30 : 10
// This is the key part
textView.typingAttributes = alignTextAttributes
// Allow system to control typing
return true
}

Answer 1

Here's what you can try -
// 4 (or 6 or 8) spaces (depending on font size)
let padding: String = " "
func textView(_ textView: UITextView, shouldChangeTextIn range: NSRange, replacementText text: String) -> Bool {
var cursorLocation = textView.selectedRange.location
if text.isEmpty {
let deleteRange = NSRange(
location: max(0, range.location - padding.count),
length: range.length + padding.count
)
textView.textStorage.replaceCharacters(in: deleteRange, with: text)
cursorLocation -= deleteRange.length
}
else {
let insertRange = NSRange(
location: range.location,
length: range.length + padding.count
)
textView.textStorage.replaceCharacters(in: insertRange, with: text.appending(padding))
cursorLocation += insertRange.length
}
textView.selectedRange.location = cursorLocation
return false
}