title: iPhone clear CGContext
body: <p>I create a circle with a nice shadow with this code (I use MonoTouch.net for iPhone, Objective-C answers are fine of course)</p>
  
  <pre><code>        UIGraphics.PushContext (ctx);
          SizeF shadowSize = new SizeF (0f, -3f);
          ctx.SetRGBFillColor (194f / 255f, 212f / 255f, 238f / 255f, 1f);
          ctx.SetAllowsAntialiasing (true);
          ctx.SetShadowWithColor (shadowSize, 20, new CGColor (0.9f, 0.7f));
          RectangleF area = new RectangleF (35f, 15f, 210f, 210f);
          ctx.FillEllipseInRect (area);
          UIGraphics.PopContext ();
  </code></pre>
  
  <p>Then I want to add to it an arc and lines. When I do, the colors and shadow etc seem to stick around? How do I 'start fresh' while drawing my UIView ? (It's all in the same UIView; I am building up the image)</p>