Drawing boxes around each digit to be entered in UITextField - swift

Question

I am trying to draw boxes around each digit entered by a user in UITextField for which keyboard type is - Number Pad.
To simplify the problem statement I assumed that each of the digits (0 to 9) will have same bounding box for its glyph, which I obtained using below code:
func getGlyphBoundingRect() -> CGRect? {
guard let font = font else {
return nil
}
// As of now taking 8 as base digit
var unichars = [UniChar]("8".utf16)
var glyphs = [CGGlyph](repeating: 0, count: unichars.count)
let gotGlyphs = CTFontGetGlyphsForCharacters(font, &unichars, &glyphs, unichars.count)
if gotGlyphs {
let cgpath = CTFontCreatePathForGlyph(font, glyphs[0], nil)!
let path = UIBezierPath(cgPath: cgpath)
return path.cgPath.boundingBoxOfPath
}
return nil
}
I am drawing each bounding box thus obtained using below code:
func configure() {
guard let boundingRect = getGlyphBoundingRect() else {
return
}
for i in 0..<length { // length denotes number of allowed digits in the box
var box = boundingRect
box.origin.x = (CGFloat(i) * boundingRect.width)
let shapeLayer = CAShapeLayer()
shapeLayer.frame = box
shapeLayer.borderWidth = 1.0
shapeLayer.borderColor = UIColor.orange.cgColor
layer.addSublayer(shapeLayer)
}
}
Now problem is -
If I am entering digits - 8,8,8 in the text field then for first occurrence of digit the bounding box drawn is aligned, however for second occurrence of same digit the bounding box appears a bit offset (by negative x), the offset value (in negative x) increases for subsequent occurrences of same digit.
Here is image for reference -
I tried to solve the problem by setting NSAttributedString.Key.kern to 0, however it did not change the behavior.
Am I missing any important property in X axis from the calculation due to which I am unable to get properly aligned bounding box over each digit? Please suggest.

Answer 1

The key function you need to use is:
protocol UITextInput {
public func firstRect(for range: UITextRange) -> CGRect
}
Here's the solution as a function:
extension UITextField {
func characterRects() -> [CGRect] {
var beginningOfRange = beginningOfDocument
var characterRects = [CGRect]()
while beginningOfRange != endOfDocument {
guard let endOfRange = position(from: beginningOfRange, offset: 1), let textRange = textRange(from: beginningOfRange, to: endOfRange) else { break }
beginningOfRange = endOfRange
var characterRect = firstRect(for: textRange)
characterRect = convert(characterRect, from: textInputView)
characterRects.append(characterRect)
}
return characterRects
}
}
Note that you may need to clip your rects if you're text is too long for the text field. Here's an example of the solution witout clipping: