NSTextStorage addAttribute for only specified range of characters - objective-c

Question

I have been working with TextKit and the NSTextStorage object on UITextView to attempt to get certain words to dynamically format.
The following method is in a subclass of UITextView and is executed on the textDidChange event. This works in that it does indeed detect when the word "the" is entered and it does color it red, however all text after the word "the" is also then red. The goal is for only "the" to be red.
Any idea what I am doing wrong?
- (void)highlight {
NSRegularExpression *regex = [NSRegularExpression regularExpressionWithPattern:#"\\bthe\\b" options:0 error:nil];
NSArray *matches = [regex matchesInString:[self text] options:0 range:NSMakeRange(0, [self.text length])];
for (NSTextCheckingResult *match in matches) {
[self.textStorage beginEditing];
[self.textStorage addAttribute:NSForegroundColorAttributeName value:[UIColor redColor] range:match.range];
[self.textStorage endEditing];
}
}

Answer 1

This is happening because NSTextStorage is actually an NSMutableAttributedString subclass, and NSMutableAttributedString works in this way: it extends attributes to inserted text.
Try subclassing NSTextStorage (to so, you need to implement four methods, as mentioned in the NSTextStorage docs). Then, implement -fixAttributesInRange: in your NSTextStorage subclass. You'll need to manage text attributes in this method (such as highlighting the word "the", in the example that you gave) manually.
One trick to improve efficiency is to reprocess as little text as possible. One way to do so is to only process text for the current paragraph that has changed:
NSRange paragaphRange = [self.string paragraphRangeForRange:self.editedRange];
Where self.editedRange will be correctly populated by your superclass to be the range of the text that has just changed.