iphone - MKOverlay not resizing smoothly

Question

I have added a MKCircle as MKOverlay to my MKMapView. Also I added an UISlider to decide the radius of the circle. Unfortunately when using this it seems a bit "laggy", not smootly like I want it to be.

Example: http://dl.dropbox.com/u/3077127/mkoverlayDelay.mov

This is my code:

- (void)addCircle
{
    // draw the radius circle for the marker
    double radius = 2000.0;
    MKCircle *circle = [MKCircle circleWithCenterCoordinate:location radius:radius];
    [circle setTitle:@"background"];
    [mapView addOverlay:circle];

    MKCircle *circleLine = [MKCircle circleWithCenterCoordinate:location radius:radius];
    [circleLine setTitle:@"line"];
    [mapView addOverlay:circleLine];
}

- (void)addCircleWithRadius:(double)radius
{
    MKCircle *circle = [MKCircle circleWithCenterCoordinate:location radius:radius];
    [circle setTitle:@"background"];
    [mapView addOverlay:circle];

    MKCircle *circleLine = [MKCircle circleWithCenterCoordinate:location radius:radius];
    [circleLine setTitle:@"line"];
    [mapView addOverlay:circleLine];
}

- (void)sliderChanged:(UISlider*)sender
{
    [mapView removeOverlays:[mapView overlays]];

    double radius = (sender.value * 100);

    [self addCircleWithRadius:radius];
}

- (MKOverlayView *)mapView:(MKMapView *)mapView viewForOverlay:(id <MKOverlay>)overlay{
    MKCircle *circle = overlay;
    MKCircleView *circleView = [[[MKCircleView alloc] initWithCircle:overlay] autorelease];

    if ([circle.title isEqualToString:@"background"])
    {
        circleView.fillColor = UIColorFromRGB(0x598DD3);
        circleView.alpha = 0.25;
    }
    else
    {
        circleView.strokeColor = UIColorFromRGB(0x5C8AC7);
        circleView.lineWidth = 2.0;
    }

    return circleView;
}

Does anybody have any suggestions on how I can smoothen this?

Best regards,
Paul Peelen

Answer 1

I have tried your code and found a very easy way to make it smoother.

If you change the order of the calls in: - (void)sliderChanged:(UISlider*)sender

You can call [self addCircleWithRadius:radius];

before calling [mapView removeOverlays:[mapView overlays]];

Just make sure you dont remove the overlays you just added, only the old ones.

This will give you a smoother resizing, specially when the new circle is smaller than the old one.

For circles that are bigger you are probably better off using NSOperations to ensure the views are created faster, this will make it smoother.

Hope this helps.