为什么MKPolyline没有显示在MKMapView上？

Question

I'm pretty new on programmin to develop iphone applications and i would like to know why the MKPolyline that I create with 2 MKMapPoints doesn't appears in the MKMapView that I insert on my view. Here is my code:

- (void)viewDidLoad
{
[super viewDidLoad];

map = [[MKMapView alloc] initWithFrame:self.view.bounds];


MKMapPoint * pointsArray = malloc(sizeof(CLLocationCoordinate2D)*4);

CLLocationCoordinate2D punto1;
punto1.latitude =39.468502;
punto1.longitude =-0.398469;


MKPointAnnotation *annotationPoint = [[MKPointAnnotation alloc]init];
annotationPoint.coordinate = punto1;
annotationPoint.title = @"Point 1";

MKPointAnnotation *annotationPoint2 = [[MKPointAnnotation alloc]init];
annotationPoint2.coordinate = CLLocationCoordinate2DMake(39.472312,-0.386453);
annotationPoint2.title = @"Point 2";


[map addAnnotation:annotationPoint];
[map addAnnotation:annotationPoint2];


pointsArray[0]= MKMapPointForCoordinate(punto1);

pointsArray[1]= MKMapPointForCoordinate(CLLocationCoordinate2DMake(39.467011,-0.390015));

pointsArray[2]= MKMapPointForCoordinate(CLLocationCoordinate2DMake(39.469926,-0.392118));

pointsArray[3]= MKMapPointForCoordinate(CLLocationCoordinate2DMake(39.472312,-0.386453));

routeLine = [MKPolyline polylineWithPoints:pointsArray count:4];

free(pointsArray);

[map addOverlay:routeLine];

MKCoordinateRegion region = MKCoordinateRegionMakeWithDistance(CLLocationCoordinate2DMake(39.467011,-0.392515), 1100, 1100);
[map setRegion:region];

[self.view insertSubview:map atIndex:0];

}

- (MKOverlayView *)mapView:(MKMapView *)mapView viewForOverlay:(id )overlay

{

MKOverlayView* overlayView = nil;

MKPolylineView  * routeLineView = [[MKPolylineView alloc] initWithPolyline:self.routeLine];


routeLineView.fillColor = [UIColor blueColor];

routeLineView.strokeColor = [UIColor orangeColor];

routeLineView.lineWidth = 3;

overlayView = routeLineView;

return overlayView;

}

The annotations are OK and they show correctly on the map. Hope someone can help, thanks!!!

Answer 1

The MKPolyline doesn't show because the map's delegate is not set.

The viewForOverlay delegate method won't get called if the map's delegate property is not set. Because the delegate method is never called, the MKPolylineView never gets created, etc...

After creating the MKMapView , set its delegate :

map = [[MKMapView alloc] initWithFrame:self.view.bounds];
map.delegate = self;  // <-- add this

I'd like to mention a few other unrelated points:

• Since you are putting MKMapPoint values in the pointsArray , the malloc should use sizeof(MKMapPoint) instead of sizeof(CLLocationCoordinate2D) . It happens to work with the wrong code because both structs happen to be the same size. But you should still use the right code.

• MKPolyline also has a polylineWithCoordinates:count: method so you can pass CLLocationCoordinate2D instead of MKMapPoint structs. This can be easier to read, understand, and avoids having to convert from coordinates to mappoints.

• The MKPolylineView uses strokeColor only so setting the fillColor for it does nothing.

• In the viewForOverlay delegate method, it's much better practice to use the overlay parameter that is passed into the method instead of the externally declared routeLine . This will be extremely important if you want to add more than one overlay. You would also first check what kind of class overlay is and then create the appropriate view for it.