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UILabel get CGRect for substring of text
// UIFont+DahDit.m
// DahDit
// Created by Erik Andersson on 2011-07-28.
// Copyright 2011 Åva gymnasium. All rights reserved.
#import "UIFont+DahDit.h"
@implementation UIFont (DahDit)
- (CGFloat)ddLineHeight
if ( [self respondsToSelector:@selector(lineHeight)] )
return self.lineHeight;
return self.leading;
// By Erik Andersson
// Please help with this method to bring support for more UILineBreakModes and text alignment
@implementation UILabel (Fix)
- (CGRect)rectForLetterAtIndex:(NSUInteger)index
NSAssert(self.lineBreakMode != UILineBreakModeClip, @"UILabel.lineBreakMode cannot be UILineBreakModeClip to calculate the rect of a character. You might think that it's possible, seeing as UILineBreakModeWordWrap is supported, and they are almost the same. But the semantics are weird. Sorry.");
NSAssert(self.lineBreakMode != UILineBreakModeHeadTruncation, @"UILabel.lineBreakMode cannot be UILineBreakModeHeadTruncation to calculate the rect of a character. We can't have everything you know.");
NSAssert(self.lineBreakMode != UILineBreakModeMiddleTruncation, @"UILabel.lineBreakMode cannot be UILineBreakModeMiddleTruncation to calculate the rect of a character. We can't have everything you know.");
NSAssert(self.lineBreakMode != UILineBreakModeTailTruncation, @"UILabel.lineBreakMode cannot be UILineBreakModeTailTruncation to calculate the rect of a character. We can't have everything you know.");
// Check if label is empty. Should add so it also checks for strings containing only spaces
if ( [self.text length] == 0 )
return self.bounds;
// Algorithm goes like this:
// 1. Determine which line the letter is on
// 2. Get the x-position on the line by: width of string up to letter
// 3. Apply UITextAlignment to the x-position
// 4. Add y position based on height of letters * line number
// Et víolà!
NSString *letter = [self.text substringWithRange:NSMakeRange(index, 1)];
// Determine which line the letter is on and the string on that line
CGSize letterSize = [letter sizeWithFont:self.font];
int lineNo = 0;
int linesDisplayed = 1;
// Get the substring with the line on it
NSUInteger lineStartsOn = 0;
NSUInteger currentLineLength = 1;
// Temporary variables
NSUInteger currentLineStartsOn = 0;
NSUInteger currentCurrentLineLength = 1;
float currentWidth;
// TODO: Add support for UILineBreakModeWordWrap, UILineBreakModeCharacterWrap to complete implementation
// Get the line number of the current letter
// Get the contents of that line
// Get the total number of lines (which means that no matter what we loop through the entire thing)
BOOL isDoneWithLine = NO;
NSUInteger i = 0, len = [self.text length];
// The loop is different depending on the lineBreakMode. If it is UILineBreakModeCharacterWrap it is easy
// just check for every single character. For UILineBreakModeWordWrap it is a bit more tedious. We have
// to think in terms of words. We have to find each word and check it. If it is longer than the frame width
// then we know we have a new word, and that lines index starts on the words beginning index.
// Spaces prove to be even morse troublesome. Several spaces in a row at the end of a line won't result in
// any more width.
for ( ; i < len; i++ )
NSString *currentLine = [self.text substringWithRange:NSMakeRange(currentLineStartsOn, currentCurrentLineLength)];
CGSize currentSize = [currentLine sizeWithFont:self.font constrainedToSize:CGSizeMake(self.frame.size.width, 1000) lineBreakMode:self.lineBreakMode];
currentWidth = currentSize.width;
if ( currentSize.height > self.font.ddLineHeight )
// We have to go to a new line
//NSLog(@"new line on: %d", i);
// If i <= index that means we are on the correct letter's line
// store that
if ( i <= index )
lineStartsOn = i;
currentLineLength = 1;
isDoneWithLine = YES;
currentLineStartsOn = i;
currentCurrentLineLength = 1;
// Okay with the same line
if ( ! isDoneWithLine )
// Make sure we didn't overstep the bounds
while ( lineStartsOn + currentLineLength > len )
// Check if linesDisplayed is faulty, if for example lines have been clipped
CGSize totalSize = [self.text sizeWithFont:self.font constrainedToSize:CGSizeMake(self.frame.size.width, 100000) lineBreakMode:self.lineBreakMode];
if ( totalSize.height > self.frame.size.height )
// It has been clipped, calculate how many lines are actually shown
linesDisplayed = 0;
float ddLineHeight = 0;
while ( ddLineHeight < self.frame.size.height )
ddLineHeight += self.font.ddLineHeight;
// Number of lines is not automatic, keep it within that range
if ( self.numberOfLines > 0 )
linesDisplayed = linesDisplayed > self.numberOfLines ? self.numberOfLines : linesDisplayed;
// Length of the substring up and including this letter
NSUInteger currentLineSubstrLength = index - lineStartsOn + 1;
currentWidth = [[self.text substringWithRange:NSMakeRange(lineStartsOn, currentLineLength)] sizeWithFont:self.font].width;
NSString *lineSubstr = [self.text substringWithRange:NSMakeRange(lineStartsOn, currentLineSubstrLength)];
float x = [lineSubstr sizeWithFont:self.font].width - [letter sizeWithFont:self.font].width;
float y = self.frame.size.height/2 - (linesDisplayed*self.font.ddLineHeight)/2 + self.font.ddLineHeight*lineNo;
if ( self.textAlignment == UITextAlignmentCenter )
x = x + (self.frame.size.width-currentWidth)/2;
else if ( self.textAlignment == UITextAlignmentRight )
x = self.frame.size.width-(currentWidth-x);
return CGRectMake(x, y, letterSize.width, letterSize.height);

Have you managed to progress this at all?


I think this solution can't handle the word wrap very well, especially for the long word which need to start a new line.

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