ios - 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.

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?

Answer 1

You may subclass from UILabel and override drawRect method:

- (void)drawRect:(CGRect)rect {
    CGContextRef ctx = UIGraphicsGetCurrentContext();
    CGContextSetRGBStrokeColor(ctx, 207.0f/255.0f, 91.0f/255.0f, 44.0f/255.0f, 1.0f); // RGBA
    CGContextSetLineWidth(ctx, 1.0f);

    CGContextMoveToPoint(ctx, 0, self.bounds.size.height - 1);
    CGContextAddLineToPoint(ctx, self.bounds.size.width, self.bounds.size.height - 1);

    CGContextStrokePath(ctx);

    [super drawRect:rect];  
}

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UPD:
As of iOS 6 Apple added NSAttributedString support for UILabel, so now it's much easier and works for multiple lines:

NSDictionary *underlineAttribute = @{NSUnderlineStyleAttributeName: @(NSUnderlineStyleSingle)};
myLabel.attributedText = [[NSAttributedString alloc] initWithString:@"Test string" 
                                                         attributes:underlineAttribute];

If you still wish to support iOS 4 and iOS 5, I'd recommend to use TTTAttributedLabel rather than underline label manually. However if you need to underline one-line UILabel and don't want to use third-party components, code above would still do the trick.