iPhone: Customizing group table cell border style

I have customized group table cell b开发者_如何转开发ackground where I am using following code to draw table cell border. The border appears correct but it always appear solid line. Is there anyway to make it etched/dotted line? What do I need to modify in following code?

 -(void)drawRect:(CGRect)rect {
    CGContextRef c = UIGraphicsGetCurrentContext();
    CGContextSetStrokeColorWithColor(c, [borderColor CGColor]);
    CGContextSetLineWidth(c, 2);
    .....

Thanks.

See CGContextSetLineDash here. This allows you to set a variety of dash patterns.