iPhone CoreText: Find the pixel coordinates of a substring

Question

Here's a screenshot of the twitter app for reference: http://screencast.com/t/YmFmYmI4M

What I want to do is place a floating pop-over on top of a substring in an NSAttributedString that could span multiple lines. NSAttributedString is a requirement for the project.

In the screenshot supplied, you can see that links are background-highlighted, so it leads me to believe that they're using CoreText and NSAttributedStrings. I also found something called CTRunRef ( http://developer.apple.com/library/ios/#documentation/Carbon/Reference/CTRunRef/Reference/reference.html ) which looks promising, but I'm having trouble fitting it all together conceptually.

In short, if I have a paragraph in core text and when I tap on a word, how do I find the bounding box for that word?

Answer 1

Set some attribute in the attributed string that won't effect display, but will cause it to be laid out as a seperate glyph run, then use CoreText to layout the string

CTFramesetterRef framesetter = CTFramesetterCreateWithAttributedString(attrString);
CTFrameRef ctframe = CTFramesetterCreateFrame(framesetter, CFRangeMake(0, 0), path, NULL);

Now you will have to hunt through the frame to find the relevant chunk of text. Get the array of CTLineRefs with CTFrameGetLines().

Iterate through the array, testing if the touch was on that line, by checking it is within the rect returned by CTLineGetImageBounds(). If it is, now look through the glyph runs in the line.

Again, you can get an array of CTRunRefs with CTLineGetGlyphRuns(). Check whether the tap was within the glyph run with CTRunGetImageBounds(), and if it was you can find the the range of indices in the original attributed string that the glyph run corresponds to with CTRunGetStringIndices().