Drawing a MKCircle on a map view - objective-c

Question

I need to draw a circle to display the distance around a point that I have plotted.
Where should I implement these two lines of code to make it work? I tried putting it in viewWillAppear: but the circle does not appear.
[self addCircle:_coordinate];
[self addCircleWithRadius:5.5 addCircleWithCoordinate:_coordinate];
- (void)addCircle: (CLLocationCoordinate2D)coordinate
{
// draw the radius circle for the marker
double radius = 2000.0;
MKCircle *circle = [MKCircle circleWithCenterCoordinate:coordinate radius:radius];
[circle setTitle:#"background"];
[_mapView addOverlay:circle];
MKCircle *circleLine = [MKCircle circleWithCenterCoordinate:coordinate radius:radius];
[circleLine setTitle:#"line"];
[_mapView addOverlay:circleLine];
}
- (void)addCircleWithRadius:(double)radius addCircleWithCoordinate: (CLLocationCoordinate2D) coordinate
{
MKCircle *circle = [MKCircle circleWithCenterCoordinate:coordinate radius:radius];
[circle setTitle:#"background"];
[_mapView addOverlay:circle];
MKCircle *circleLine = [MKCircle circleWithCenterCoordinate:coordinate radius:radius];
[circleLine setTitle:#"line"];
[_mapView addOverlay:circleLine];
}
- (void)sliderChanged:(UISlider*)sender
{
[_mapView removeOverlays:[_mapView overlays]];
double radius = (sender.value * 100);
CLLocationCoordinate2D coordinate = self.coordinate;
[self addCircleWithRadius:radius addCircleWithCoordinate:coordinate];
}
- (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;
}

Answer 1

While you could try viewDidAppear instead of viewWillAppear, I think it should already work in that regard. I think that you have something else wrong, and you should step through with a debugger to find it. Check the usual suspects:
Set the fill color. Make it opaque and obvious.
_mapView might be nil or zombied during runtime. (or not mapped in your xib)
The coordinates or radius may be different than you expect. Check the actual coordinate values in your debugger.
Everything may be correct except that the coordinates are not located in your map's zoomed area.