Can I use NSAttributedString in Core Text in iOS?

Question

I'm trying to work out how to take an NSAttributedString and use it in Core Text on the iPad. I watched one of the WWDC videos (110) which has slides (but no source code) and it describes how to create an NSAttributedString, then just put it into a CTFramesetterRef:

CTFontRef helveticaBold = CTFontCreateWithName( CFSTR("Helvetica-Bold"), 24.0, NULL);

NSString* unicodeString = NSLocalizedString(@"TitleString", @"Window Title");
CGColorRef color = [UIColor blueColor].CGColor; NSNumber* underline = [NSNumber numberWithInt:kCTUnderlineStyleSingle|kCTUnderlinePatternDot];
NSDictionary* attributesDict = [NSDictionary dictionaryWithObjectsAndKeys:helveticaBold, (NSString*)kCTFontAttributeName, color, (NSString*)kCTForegroundColorAttributeName, underline, (NSString*)kCTUnderlineStyleAttributeName, nil];
NSAttributedString* stringToDraw = [[NSAttributedString alloc] initWithString:unicodeString attributes:attributesDict];

CTFramesetterRef framesetter = CTFramesetterCreateWithAttributedString(stringToDraw);

CTFrameRef frame = CTFramesetterCreateFrame(framesetter, CFRangeMake(0, 0), path, NULL);
CFRelease(framesetter);
CTFrameDraw(frame, context);
CFRelease(frame);

But when I try this, it throws the error:

Passing argument 1 of 'CTFramesetterCreateWithAttributedString' from incompatible pointer type

Are CFAttributedString and NSAttributedString 'toll-free bridged'? I've read somewhere that this is only true on OSX, but this is how Apple do it in their demo...

Thanks!

:-Joe

Answer 1

You're almost there. Just cast the CTFontRef to an id type when you add it to the attributes dictionary.

CTFontRef helveticaBold = CTFontCreateWithName( CFSTR("Helvetica-Bold"), 24.0, NULL);

NSString* unicodeString = NSLocalizedString(@"TitleString", @"Window Title");

CGColorRef color = [UIColor blueColor].CGColor; 
NSNumber* underline = [NSNumber numberWithInt:
    kCTUnderlineStyleSingle|kCTUnderlinePatternDot];

NSDictionary* attributesDict = [NSDictionary dictionaryWithObjectsAndKeys:
                    (id)helveticaBold, (NSString*)kCTFontAttributeName, 
                    color, (NSString*)kCTForegroundColorAttributeName, 
                    underline, (NSString*)kCTUnderlineStyleAttributeName, nil];

NSAttributedString* stringToDraw = [[NSAttributedString alloc] 
                            initWithString:unicodeString
                            attributes:attributesDict];

Answer 2

the code of WWDC Session 110 CTPageViewer is now part of Apple's official sample code:

http://developer.apple.com/library/ios/#samplecode/CoreTextPageViewer/Listings/ReadMe_txt.html

Answer 3

You can download the WWDC10 source code here. In addition, use toll-free bridging and explicitly cast your stringToDraw to a CFAttributedStringRef.