Underline text in UIlabel

Question

How can I underline a text that could be multiple lines of string? I find some people suggest UIWebView, but it is obviously too heavy a class for just text rendering.

My thoughts was to figure out the start point and length of each string in each line. And draw a line under it accordingly.

I meet problems at how to figure out the length and start point for the string. Can anybody help me on this?

I tried to use -[UILabel textRectForBounds:limitedToNumberOfLines:], this should be the drawing bounding rect for the text right? Then I have to work on the alignment? How can I get the start point of each line when it is center-justified and right justified?

I am new here, so thank you in advance.

Answer 1

Use an attribute string:

NSMutableAttributedString* attrString = [[NSMutableAttributedString alloc] initWithString:@"Your String"]
[attrString addAttribute:(NSString*)kCTUnderlineStyleAttributeName 
                   value:[NSNumber numberWithInt:kCTUnderlineStyleSingle] 
                   range:(NSRange){0,[attrString length]}];

And then override the label - (void)drawTextInRect:(CGRect)aRect and render the text in something like:

CGContextRef ctx = UIGraphicsGetCurrentContext();
CGContextSaveGState(ctx);
CTFramesetterRef framesetter = CTFramesetterCreateWithAttributedString((CFAttributedStringRef)attrString);
drawingRect = self.bounds;
CGMutablePathRef path = CGPathCreateMutable();
CGPathAddRect(path, NULL, drawingRect);
textFrame = CTFramesetterCreateFrame(framesetter,CFRangeMake(0,0), path, NULL);
CGPathRelease(path);
CFRelease(framesetter);
CTFrameDraw(textFrame, ctx);
CGContextRestoreGState(ctx);

Or better yet instead of overriding just use the OHAttributedLabel created by Olivier Halligon