Transcript MapKitOverlay

Overlay on a Map
• Overlays can be added to a map to highlight
an area of interest or a route, ..
• Can be standard or user-defined
• We will focus on standard overlays (circles,
polygons)
Overlay on a Map
• To add an overlay to a map (a MKMapView
object), we call the method addOverlay
• -(void) addOverlay: (id <MKOverlay>)
overlay;
•  what does (id <MKOverlay>) mean (that
is the data type of the parameter)?
Overlay on a Map
•  what does (id <MKOverlay>) mean?
• It means an object that conforms to the
MKOverlay protocol
• MKCircle, MKPolygon are classes that
conform to the MKOverlay protocol
Overlay on a Map
• We will use MKCircle to add a circle
overlay to our map
• Use circleWithCenterCoordinate:radius:
method to create a MKCircle object
• Takes 2 parameters: a
CLLocationCoordinate2D (for the center of
the circle) and a CLLocationDistance (for
the radius of the circle, in meters)
MKMapView class
MKCircle *circle = [MKCircle
circleWithCenterCoordinate:
whiteHouse.coordinate radius: 200];
[map addOverlay: circle];
MKMapView class
• MKMapView has a delegate, of type (id
<MKMapViewDelegate>), i.e. an object
implementing the MKMapViewDelegate protocol
• A map view object sends messages to its delegate
regarding the loading of the map data and changes
in the portion of the map being displayed; the
delegate also manages annotation views to
highlight points of interest on the map
Overlay on a Map
• addOverlay automatically calls the method
• (MKOverlayRenderer *) mapView:
(MKMapView *) mapView
rendererForOverlay:(id) <MKOverlay>)
overlay
• of the delegate of the MKMapView, which
is of type ( id <MKMapViewDelegate>)
Overlay on a Map
• That method,
mapView:rendererForOverlay:, is the
method doing the work to add the overlay
•  we need to code in a class that
implements the MKMapViewDelegate
protocol
• And set the delegate of the MKMapView to
be an object of that class
Overlay on a Map
• The easiest is for our ViewController class
to implement the MKMapViewDelegate
protocol, set the delegate of the
MKMapView to self, and implement the
mapView:rendererForOverlay: inside our
ViewController class
MKMapView class
@interface OurViewController :
UIViewController <MKMapViewDelegate>
{
IBOutlet MKMapView *map;
}
MKMapView class
• self is an object that conforms to the
MKMapViewDelegate protocol
•  self can be the delegate of map
• In the .m file, we will set that up
map.delegate = self;
MKMapView class
• Now we can override the mapView:
rendererForOverlay: method inside our
ViewController class
• .. which is the method automatically called
when we call addOverlay with a
MKMapView object (map in this case)
mapView:rendererForOverlay:
method
• (MKOverlayRenderer *) mapView:
(MKMapView *) mapView
rendererForOverlay:(id) <MKOverlay>)
overlay
• Inside that method, build a
MKOverlayRenderer object and return it
MKCircleRenderer class
• The MKCircleRenderer class, which
inherits from MKOverlayRenderer  a
MKCircleRenderer object “is a”
MKOverlayRenderer object
• It provides a visual representation for a
MKCircle overlay object
mapView:rendererForOverlay:
method
• The overlay parameter is the MKCircle
passed to addOverlay earlier
•  check it out using NSLog
MKCircleRenderer *circleRenderer =
[[MKCircleRenderer alloc]
initWithOverlay: overlay];
mapView:rendererForOverlay:
method
• Set stroke and fill colors
circleRenderer.strokeColor = [UIColor
redColor];
circleRenderer.fillColor = [[UIColor
redColor] colorWithAlphaComponent: 0.5];
return circleRenderer;