Core Text - CFStringGetParagraphBounds and Setting Paragraph Styles

I am working through the text classes writing unit tests. As Cello had no unit tests before I took on the OSX port I have been writing unit tests primarily for the delta, that is the changes I have made, rather than attempting to add unit tests for the all of the historic code. Sure I would love to but that is a project in it's self. I would hope that as I find bugs in the code (sure as are eggs are eggs there will be bugs) that I can add unit tests that demonstrate the bug and the fix after I have made it - but I will have to see.

I am using CFAttributedStringSetAttribute to add a paragraph style to the backing store. The only wrinkle here is that the style should be applied to the whole paragraph. Cello's pre Core Text code ensures that if you apply a paragraph style to a text range that the paragraph style will apply to complete paragraphs.

My hope was that CFAttributedStringSetAttribute with kCTParagraphStyleAttributeName would magically do this. It was a small hope and I quickly unvovered the folly of it when I wrote the unit test. Fortunately Core Foundation has a function CFStringGetParagraphBounds that will calculate the start and end points of a paragraph. The code falls out something like this.


CFRange selectedRange;
CFAttributedString attributedString;
CTParagraphStyleRef paragraphStyle;

// get the underlying string
CFStringRef str = CFAttributedStringGetString(attributedString);

CFIndex parBeginIndex, parEndIndex;

// get the get the bounds of the paragraph
CFStringGetParagraphBounds(str, selectedRange, &parBeginIndex, &parEndIndex, NULL);

// convert it to a CFRange
CFRange paragraphRange = CFRangeMake(parBeginIndex, parEndIndex - parBeginIndex);

// Set the attributes
CFAttributedStringSetAttribute(attributedString, paragraphRange, kCTParagraphStyleAttributeName, paragraphStyle);