title: MapKit: Update radius property of MKCircle overlay without flickering
body: <p>I have a <em>MKMapView</em> (self.mapView) to which I add a <em>MKCircle</em> overlay (self.radiusOverlay) with a specific radius (self.location.radius). </p>
  
  <p>Right below the <em>MKMapView</em> there is a <em>UISlider</em> (self.radiusSlider) which changes the overlay's radius on <em>Value Changed</em>:</p>
  
  <pre><code>- (void)viewWillAppear:(BOOL)animated {
  
      self.radiusOverlay = [MKCircle circleWithCenterCoordinate:CLLocationCoordinate2DMake([self.location.latitude floatValue], [self.location.longitude floatValue]) radius:[self.location.radius floatValue]];
  
      [self.mapView addOverlay:self.radiusOverlay];
  
      self.radiusSlider.value = [self.location.radius floatValue];
  }
  </code></pre>
  
  <p>This is the method which does the radius-updating stuff:</p>
  
  <pre><code>- (IBAction)updateLocationRadius:(UISlider *)sender {
  
      [self.mapView removeOverlay:self.radiusOverlay];
  
      self.location.radius = [NSNumber numberWithFloat:sender.value];
  
      self.radiusOverlay = [MKCircle circleWithCenterCoordinate:CLLocationCoordinate2DMake([self.location.latitude floatValue], [self.location.longitude floatValue]) radius:[self.location.radius floatValue]];
      [self.mapView addOverlay:self.radiusOverlay];
  }
  </code></pre>
  
  <p>This works fine, but it's not looking good: By removing and re-adding <em>self.radiusOverlay</em> I cause the overlay to flicker.</p>
  
  <p>What can I do to avoid this flickering?</p>