size - Page 78 - Developer IT

Scaling MKMapView Annotations relative to the zoom level

- by Jonathan

The Problem I'm trying to create a visual radius circle around a annonation, that remains at a fixed size in real terms. Eg. So If i set the radius to 100m, as you zoom out of the Map view the radius circle gets progressively smaller. I've been able to achieve the scaling, however the radius rect/circle seems to "Jitter" away from the Pin Placemark as the user manipulates the view. The Manifestation Here is a video of the behaviour. The Implementation The annotations are added to the Mapview in the usual fashion, and i've used the delegate method on my UIViewController Subclass (MapViewController) to see when the region changes. -(void)mapView:(MKMapView *)pMapView regionDidChangeAnimated:(BOOL)animated{ //Get the map view MKCoordinateRegion region; CGRect rect; //Scale the annotations for( id<MKAnnotation> annotation in [[self mapView] annotations] ){ if( [annotation isKindOfClass: [Location class]] && [annotation conformsToProtocol:@protocol(MKAnnotation)] ){ //Approximately 200 m radius region.span.latitudeDelta = 0.002f; region.span.longitudeDelta = 0.002f; region.center = [annotation coordinate]; rect = [[self mapView] convertRegion:foo toRectToView: self.mapView]; if( [[[self mapView] viewForAnnotation: annotation] respondsToSelector:@selector(setRadiusFrame:)] ){ [[[self mapView] viewForAnnotation: annotation] setRadiusFrame:rect]; } } } The Annotation object (LocationAnnotationView)is a subclass of the MKAnnotationView and it's setRadiusFrame looks like this -(void) setRadiusFrame:(CGRect) rect{ CGPoint centerPoint; //Invert centerPoint.x = (rect.size.width/2) * -1; centerPoint.y = 0 + 55 + ((rect.size.height/2) * -1); rect.origin = centerPoint; [self.radiusView setFrame:rect]; } And finally the radiusView object is a subclass of a UIView, that overrides the drawRect method to draw the translucent circles. setFrame is also over ridden in this UIView subclass, but it only serves to call [UIView setNeedsDisplay] in addition to [UIView setFrame:] to ensure that the view is redrawn after the frame has been updated. The radiusView object's (CircleView) drawRect method looks like this -(void) drawRect:(CGRect)rect{ //NSLog(@"[CircleView drawRect]"); [self setBackgroundColor:[UIColor clearColor]]; //Declarations CGContextRef context; CGMutablePathRef path; //Assignments context = UIGraphicsGetCurrentContext(); path = CGPathCreateMutable(); //Alter the rect so the circle isn't cliped //Calculate the biggest size circle if( rect.size.height > rect.size.width ){ rect.size.height = rect.size.width; } else if( rect.size.height < rect.size.width ){ rect.size.width = rect.size.height; } rect.size.height -= 4; rect.size.width -= 4; rect.origin.x += 2; rect.origin.y += 2; //Create paths CGPathAddEllipseInRect(path, NULL, rect ); //Create colors [[self areaColor] setFill]; CGContextAddPath( context, path); CGContextFillPath( context ); [[self borderColor] setStroke]; CGContextSetLineWidth( context, 2.0f ); CGContextSetLineCap(context, kCGLineCapSquare); CGContextAddPath(context, path ); CGContextStrokePath( context ); CGPathRelease( path ); //CGContextRestoreGState( context ); } Thanks for bearing with me, any help is appreciated. Jonathan

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