How do I locate the CGRect for a substring of text in a UILabel?

Can you instead base your class on UITextView? If so, check out the UiTextInput protocol methods. See in particular the geometry and hit resting methods.

My suggestion would be to make use of Text Kit. Unfortunately we don't have access to the layout manager that a UILabel uses however it might be possible to create a replica of it and use that to get the rect for a range.

My suggestion would be to create a NSTextStorage object containing the exact same attributed text as is in your label. Next create a NSLayoutManager and add that to the the text storage object. Finally create a NSTextContainer with the same size as the label and add that to the layout manager.

Now the text storage has the same text as the label and the text container is the same size as the label so we should be able to ask the layout manager we created for a rect for our range using boundingRectForGlyphRange:inTextContainer:. Make sure you convert your character range to a glyph range first using glyphRangeForCharacterRange:actualCharacterRange: on the layout manager object.

All going well that should give you a bounding CGRect of the range you specified within the label.

I haven't tested this but this would be my approach and by mimicking how the UILabel itself works should have a good chance of succeeding.

Following Joshua's answer in code, I came up with the following which seems to work well:

- (CGRect)boundingRectForCharacterRange:(NSRange)range
{
NSTextStorage *textStorage = [[NSTextStorage alloc] initWithAttributedString:[self attributedText]];
NSLayoutManager *layoutManager = [[NSLayoutManager alloc] init];
[textStorage addLayoutManager:layoutManager];
NSTextContainer *textContainer = [[NSTextContainer alloc] initWithSize:[self bounds].size];
textContainer.lineFragmentPadding = 0;
[layoutManager addTextContainer:textContainer];


NSRange glyphRange;


// Convert the range for glyphs.
[layoutManager characterRangeForGlyphRange:range actualGlyphRange:&glyphRange];


return [layoutManager boundingRectForGlyphRange:glyphRange inTextContainer:textContainer];
}

Another way of doing this, if you have automatic font size adjustment enabled, would be like this:

let stringLength: Int = countElements(self.attributedText!.string)
let substring = (self.attributedText!.string as NSString).substringWithRange(substringRange)


//First, confirm that the range is within the size of the attributed label
if (substringRange.location + substringRange.length  > stringLength)
{
return CGRectZero
}


//Second, get the rect of the label as a whole.
let textRect: CGRect = self.textRectForBounds(self.bounds, limitedToNumberOfLines: self.numberOfLines)


let path: CGMutablePathRef = CGPathCreateMutable()
CGPathAddRect(path, nil, textRect)
let framesetter = CTFramesetterCreateWithAttributedString(self.attributedText)
let tempFrame: CTFrameRef = CTFramesetterCreateFrame(framesetter, CFRangeMake(0, stringLength), path, nil)
if (CFArrayGetCount(CTFrameGetLines(tempFrame)) == 0)
{
return CGRectZero
}


let lines: CFArrayRef = CTFrameGetLines(tempFrame)
let numberOfLines: Int = self.numberOfLines > 0 ? min(self.numberOfLines, CFArrayGetCount(lines)) :  CFArrayGetCount(lines)
if (numberOfLines == 0)
{
return CGRectZero
}


var returnRect: CGRect = CGRectZero


let nsLinesArray: NSArray = CTFrameGetLines(tempFrame) // Use NSArray to bridge to Array
let ctLinesArray = nsLinesArray as Array
var lineOriginsArray = [CGPoint](count:ctLinesArray.count, repeatedValue: CGPointZero)


CTFrameGetLineOrigins(tempFrame, CFRangeMake(0, numberOfLines), &lineOriginsArray)


for (var lineIndex: CFIndex = 0; lineIndex < numberOfLines; lineIndex++)
{
let lineOrigin: CGPoint = lineOriginsArray[lineIndex]
let line: CTLineRef = unsafeBitCast(CFArrayGetValueAtIndex(lines, lineIndex), CTLineRef.self) //CFArrayGetValueAtIndex(lines, lineIndex)
let lineRange: CFRange = CTLineGetStringRange(line)


if ((lineRange.location <= substringRange.location) && (lineRange.location + lineRange.length >= substringRange.location + substringRange.length))
{
var charIndex: CFIndex = substringRange.location - lineRange.location; // That's the relative location of the line
var secondary: CGFloat = 0.0
let xOffset: CGFloat = CTLineGetOffsetForStringIndex(line, charIndex, &secondary);


// Get bounding information of line


var ascent: CGFloat = 0.0
var descent: CGFloat = 0.0
var leading: CGFloat = 0.0


let width: Double = CTLineGetTypographicBounds(line, &ascent, &descent, &leading)
let yMin: CGFloat = floor(lineOrigin.y - descent);
let yMax: CGFloat = ceil(lineOrigin.y + ascent);


let yOffset: CGFloat = ((yMax - yMin) * CGFloat(lineIndex))


returnRect = (substring as NSString).boundingRect(with: CGSize(width: Double.greatestFiniteMagnitude, height: Double.greatestFiniteMagnitude), options: .usesLineFragmentOrigin, attributes: [.font: self.font ?? UIFont.systemFont(ofSize: 1)], context: nil)
returnRect.origin.x = xOffset + self.frame.origin.x
returnRect.origin.y = yOffset + self.frame.origin.y + ((self.frame.size.height - textRect.size.height) / 2)


break
}
}


return returnRect

Building off of Luke Rogers's answer but written in swift:

Swift 2

extension UILabel {
func boundingRectForCharacterRange(_ range: NSRange) -> CGRect? {


guard let attributedText = attributedText else { return nil }


let textStorage = NSTextStorage(attributedString: attributedText)
let layoutManager = NSLayoutManager()


textStorage.addLayoutManager(layoutManager)


let textContainer = NSTextContainer(size: bounds.size)
textContainer.lineFragmentPadding = 0.0


layoutManager.addTextContainer(textContainer)


var glyphRange = NSRange()


// Convert the range for glyphs.
layoutManager.characterRangeForGlyphRange(range, actualGlyphRange: &glyphRange)


return layoutManager.boundingRectForGlyphRange(glyphRange, inTextContainer: textContainer)
}
}

Example Usage (Swift 2)

let label = UILabel()
let text = "aa bb cc"
label.attributedText = NSAttributedString(string: text)
let sublayer = CALayer()
sublayer.borderWidth = 1
sublayer.frame = label.boundingRectForCharacterRange(NSRange(text.range(of: "bb")!, in: text))
label.layer.addSublayer(sublayer)

Swift 3/4

extension UILabel {
func boundingRect(forCharacterRange range: NSRange) -> CGRect? {


guard let attributedText = attributedText else { return nil }


let textStorage = NSTextStorage(attributedString: attributedText)
let layoutManager = NSLayoutManager()


textStorage.addLayoutManager(layoutManager)


let textContainer = NSTextContainer(size: bounds.size)
textContainer.lineFragmentPadding = 0.0


layoutManager.addTextContainer(textContainer)


var glyphRange = NSRange()


// Convert the range for glyphs.
layoutManager.characterRange(forGlyphRange: range, actualGlyphRange: &glyphRange)


return layoutManager.boundingRect(forGlyphRange: glyphRange, in: textContainer)
}
}

Example Usage (Swift 3/4)

let label = UILabel()
let text = "aa bb cc"
label.attributedText = NSAttributedString(string: text)
let sublayer = CALayer()
sublayer.borderWidth = 1
sublayer.frame = label.boundingRect(forCharacterRange: NSRange(text.range(of: "bb")!, in: text))
label.layer.addSublayer(sublayer)

For anyone who's looking for a plain text extension!

extension UILabel {
func boundingRectForCharacterRange(range: NSRange) -> CGRect? {
guard let text = text else { return nil }


let textStorage = NSTextStorage.init(string: text)
let layoutManager = NSLayoutManager()


textStorage.addLayoutManager(layoutManager)


let textContainer = NSTextContainer(size: bounds.size)
textContainer.lineFragmentPadding = 0.0


layoutManager.addTextContainer(textContainer)


var glyphRange = NSRange()


// Convert the range for glyphs.
layoutManager.characterRange(forGlyphRange: range, actualGlyphRange: &glyphRange)


return layoutManager.boundingRect(forGlyphRange: glyphRange, in: textContainer)
}
}

_{P.S. Updated answer of Noodle of Death`s answer.}

swift 4 solution, will work even for multiline strings, bounds were replaced with intrinsicContentSize

extension UILabel {
func boundingRectForCharacterRange(range: NSRange) -> CGRect? {


guard let attributedText = attributedText else { return nil }


let textStorage = NSTextStorage(attributedString: attributedText)
let layoutManager = NSLayoutManager()


textStorage.addLayoutManager(layoutManager)


let textContainer = NSTextContainer(size: intrinsicContentSize)


textContainer.lineFragmentPadding = 0.0


layoutManager.addTextContainer(textContainer)


var glyphRange = NSRange()


layoutManager.characterRange(forGlyphRange: range, actualGlyphRange: &glyphRange)


return layoutManager.boundingRect(forGlyphRange: glyphRange, in: textContainer)
}
}

The proper answer is you actually can't. Most of the solutions here trying to re-create UILabel internal behavior with varying precision. It just so happens that in recent iOS versions UILabel renders text using TextKit/CoreText frameworks. In earlier versions it actually used WebKit under the hood. Who knows what it will use in future. Reproducing with TextKit have obvious problems even right now (not talking about future-proof solutions). We don't quite know (or can't guarantee) how the text layout and rendering are actually performed, i.e. which parameters are used – just look at all the edge cases mentioned. Some solution may 'accidentally' work for you for some simple cases you tested – that doesn't guarantee anything even within current version of iOS. Text rendering is hard, don't get me started on RTL support, Dynamic Type, emojis etc.

If you need a proper solution just don't use UILabel. It is simple component and the fact that its TextKit internals aren't exposed in the API is a clear indication that Apple don't want developers to build solutions relying on this implementation detail.

Alternatively you can use UITextView. It conveniently exposes its TextKit internals and is very configurable so you can achieve almost everything UILabel is good for.

You may also just go lower level and use TextKit directly (or even lower with CoreText). Chances are, if you actually need to find text positions you may soon need other powerful tools available in these frameworks. They are rather hard to use at first but I feel like most of the complexity comes from actually learning how text layout and rendering works – and that's a very relevant and useful skill. Once you get familiar with Apple's excellent text frameworks you will feel empowered to do so much more with text.

I'm not keen on feeding in ranges as a parameter because I'm lazy. I'd rather have the method find the range for me. With that in mind, I've adapted NoodleOfDeath's answer above to take a String as a parameter.

extension String {
func nsRange(of substring: String) -> NSRange? {
// Get the swift range
guard let range = range(of: substring) else { return nil }


// Get the distance to the start of the substring
let start = distance(from: startIndex, to: range.lowerBound) as Int
//Get the distance to the end of the substring
let end = distance(from: startIndex, to: range.upperBound) as Int


//length = endOfSubstring - startOfSubstring
//start = startOfSubstring
return NSMakeRange(start, end - start)
}
}




extension UILabel {
/// Finds the bounding rect of a substring in a `UILabel`
/// - Parameter substring: The substring whose bounding box you'd like to determine
/// - Returns: An optional `CGRect`
func boundingRect(for substring: String) -> CGRect? {
guard let attributedText = attributedText,
let text = self.text,
let range: NSRange = text.nsRange(of: substring) else {
return nil
}


let textStorage = NSTextStorage(attributedString: attributedText)
let layoutManager = NSLayoutManager()
textStorage.addLayoutManager(layoutManager)
let textContainer = NSTextContainer(size: bounds.size)
textContainer.lineFragmentPadding = 0.0
layoutManager.addTextContainer(textContainer)
var glyphRange = NSRange()
layoutManager.characterRange(forGlyphRange: range, actualGlyphRange: &glyphRange)


return layoutManager.boundingRect(forGlyphRange: glyphRange, in: textContainer)
}
}