title: drawRect is not refreshing the screen
body: <p>I have this code in my drawRect method  </p>
  
  <pre><code>float aValue = .0167f;
  float fValue = 20;
  for(int i=1; i&lt;=6; i++)
          {
  
              CGContextSelectFont(context, "Arial", fValue, kCGEncodingMacRoman);
              CGContextSetCharacterSpacing(context, 0);
              CGContextSetTextDrawingMode(context, kCGTextFill);
  
              NSString *hString = [[NSString alloc] initWithFormat:@"%i",i];
  
  
              CGContextSetRGBFillColor(context, 1, 1, 1, aValue);
              CGContextShowTextAtPoint(context, i*25, i*16, [hString UTF8String], [hString length]);
              aValue += 0.167;
              fValue += 1;
  
          }
  </code></pre>
  
  <p>I am calling a method using NSTimer like this  </p>
  
  <pre><code>staticTimer = [NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:@selector(refreshUIView) userInfo:nil repeats:YES];
  </code></pre>
  
  <p>here is the refreshUIView  </p>
  
  <pre><code>-(void)refreshUIView
  {
      [self setNeedsDisplay];
  }
  </code></pre>
  
  <p>Problem is that drawRect is not clearing the screen, its just over writing what have been written last time on screen. </p>