UIControl for a Needle Gauge aka Google O Meter

For those times when a UISlider just isn't fun enough I was thinking I'd work up a custom UIControl to do something similar to a Google O Meter from the google chart API on iOS.

Here's an example of what I'm talking about visually. My goal would be to enable touch manipulation of the needle an开发者_JAVA技巧d easy customization of the range labels and coloring gradients. The Google Charts API is a great inspiration:

Before I re-invent the wheel is anyone aware of an existing effort I could leverage good sample code with something like this or project I could contribute too?

Thanks for any pointers.

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I have implemented a GaugeView as a child of UIView and added the code to draw the gauge in the drawRect method. Nothing fancy but may be helpful to start

 - (void)drawRect:(CGRect)rect {

     [super drawRect:rect];
     CGRect parentViewBounds = self.bounds;
     CGFloat x = CGRectGetWidth(parentViewBounds)/2;
     CGFloat y = CGRectGetHeight(parentViewBounds);
     CGFloat radius = y;
     CGFloat percent_angle = _progress * M_PI;

     CGContextRef ctx = UIGraphicsGetCurrentContext();
     CGContextBeginPath(ctx);

     // Add path
     CGFloat m2_x = radius * (1.0 - 0.9*cos(percent_angle));
     CGFloat m2_y = radius * (1.0 - 0.9*sin(percent_angle));      

     CGContextBeginPath(ctx);
     CGContextAddArc(ctx, x, y, radius, M_PI, 0, 0);
     CGContextAddLineToPoint(ctx, x + 0.1*radius, y);
     CGContextAddArc(ctx, x, y, 0.1*radius, 0, M_PI, 1);
     CGContextClosePath(ctx);
     CGContextSetFillColorWithColor(ctx,[UIColor whiteColor].CGColor);
     CGContextFillPath(ctx);

     CGContextBeginPath(ctx);
     CGContextMoveToPoint(ctx, m2_x, m2_y);
     CGContextAddArc(ctx, x, y, 0.9*radius, M_PI + percent_angle, M_PI, 1);
     CGContextAddLineToPoint(ctx, 0.8*radius, y);
     CGContextSetStrokeColorWithColor(ctx,self.fillColor.CGColor);
     CGContextAddArc(ctx, x, y, 0.2*radius, M_PI, M_PI + percent_angle, 0);
     CGContextClosePath(ctx);
     CGContextStrokePath(ctx);

     CGContextBeginPath(ctx);
     CGContextMoveToPoint(ctx, m2_x, m2_y);
     CGContextSetFillColorWithColor(ctx,self.fillColor.CGColor);
     CGContextAddArc(ctx, x, y, 0.9*radius, M_PI + percent_angle, M_PI, 1);
     CGContextAddLineToPoint(ctx, 0.8*radius, y);
     CGContextAddArc(ctx, x, y, 0.2*radius, M_PI, M_PI + percent_angle, 0);
     CGContextClosePath(ctx);
     CGContextFillPath(ctx);

    /* CGContextBeginPath(ctx);
     CGContextAddArc(ctx, x, y, radius, M_PI, 0, 0);
     CGContextAddLineToPoint(ctx, x + 0.1*radius, y);
     CGContextAddArc(ctx, x, y, 0.1*radius, 0, M_PI, 1);
     CGContextClosePath(ctx);
     CGContextSetStrokeColorWithColor(ctx,[self.strokeColor CGColor]);
     CGContextStrokePath(ctx);*/

     for(int i = 0; i < 100; i++)
     {
         CGFloat angle =M_PI * 0.01 * i;
         CGFloat l1_x = radius * (1.0 - 0.98*cos(angle));
         CGFloat l1_y = radius * (1.0 - 0.98*sin(angle));
         if(i%10 == 0)
         {
             l1_x = radius * (1.0 - 0.9*cos(angle));
             l1_y = radius * (1.0 - 0.9*sin(angle));
         }
         else if(i%5 == 0)
         {
             l1_x = radius * (1.0 - 0.95*cos(angle));
             l1_y = radius * (1.0 - 0.95*sin(angle));             
         }

         CGFloat l2_x = radius * (1.0 - cos(angle));
         CGFloat l2_y = radius * (1.0 - sin(angle)); 
         CGContextMoveToPoint(ctx, l1_x, l1_y);
         CGContextSetLineWidth(ctx, 1.0);
         CGContextAddLineToPoint(ctx, l2_x, l2_y);
         CGContextSetStrokeColorWithColor(ctx,[self.strokeColor CGColor]);
         CGContextStrokePath(ctx);
     }

     CGFloat n1_x = radius * (1.0 - 0.1*cos(percent_angle));
     CGFloat n1_y = radius * (1.0 - 0.1*sin(percent_angle));
     CGFloat n2_x = radius * (1.0 - cos(percent_angle));
     CGFloat n2_y = radius * (1.0 - sin(percent_angle)); 
     CGContextMoveToPoint(ctx, n1_x, n1_y);
     CGContextSetLineWidth(ctx, 4.0);
     CGContextAddLineToPoint(ctx, n2_x, n2_y);
     CGContextSetStrokeColorWithColor(ctx,[self.needleColor CGColor]);
     CGContextStrokePath(ctx);

 }