问题
New to Map Overlays, but this is a really weird problem.
I pass in the mapView.visibleMapRect to my overlay implementation and return that as the boundingMapRect, which is fine for now - just trying to draw a line on the whole map rect.
My drawMapRect is getting called, and in the following code - the partially transparent green rectangle is drawn, but the lines are not. I've verified the line drawing code in drawRect of a uiview subclass, so I know it draws something :-)
I'm sure I must be missing something easy, but I can't see it :-)
The thing that throws me off is that the visibleMapRect, when converted to a CGRect has very strange coordinates - they don't look like screen coordinates to me at all - which seems like the source of the problem to me.
Any help would be greatly appreciated:
The drawMapRect is called multiple times, i'm attaching the output below.
Thanks, Bob
ViewController setup code:
CLLocationCoordinate2D center;
center.latitude = 29.46;
center.longitude = -98.30;
MKCoordinateRegion region;
MKCoordinateSpan span;
span.latitudeDelta = 0.2;
span.longitudeDelta = 0.2;
region.center = center;
region.span = span;
self.mapView.region = region;
MyOverlay *myoverlay = [[MyOverlay alloc] initWithCoordinate: center andBoundingRect: self.mapView.visibleMapRect];
[self.mapView addOverlay:myoverlay];
MyOverlay code:
@implementation MyOverlay
@synthesize coordinate;
@synthesize boundingMapRect;
- (id) initWithCoordinate: (CLLocationCoordinate2D) coord andBoundingRect: (MKMapRect) bRect {
if ((self = [super init])) {
//customize here
coordinate = coord;
boundingMapRect = bRect;
}
return self;
}
MyOverlayView drawing code
- (void)drawMapRect:(MKMapRect)mapRect zoomScale:(MKZoomScale)zoomScale inContext:(CGContextRef)context {
CGRect theRect = [self rectForMapRect:mapRect];
NSLog(@"in drawMapRect ...theRect is %f, %f, size of %f x %f", theRect.origin.x, theRect.origin.y, theRect.size.width, theRect.size.height);
CGContextSetAlpha(context, 1.0);
CGContextSetStrokeColorWithColor(context, [UIColor blueColor].CGColor);
CGContextMoveToPoint(context, theRect.origin.x, theRect.origin.y);
CGContextAddLineToPoint(context, theRect.size.width, theRect.size.width);
CGContextSetAlpha(context, .25);
CGContextSetFillColorWithColor(context, [UIColor greenColor].CGColor);
CGContextFillRect(context, theRect);
}
Output
2011-05-16 11:25:18.037 coolOverlayTest[71661:7903] in drawMapRect ...theRect is 61440.000000, 37888.000000, size of 262144.000000 x 262144.000000
2011-05-16 11:25:18.038 coolOverlayTest[71661:760b] in drawMapRect ...theRect is 323584.000000, 37888.000000, size of 262144.000000 x 262144.000000
2011-05-16 11:25:18.042 coolOverlayTest[71661:7903] in drawMapRect ...theRect is 323584.000000, 37888.000000, size of 262144.000000 x 262144.000000
2011-05-16 11:25:18.044 coolOverlayTest[71661:760b] in drawMapRect ...theRect is -200704.000000, 37888.000000, size of 262144.000000 x 262144.000000
2011-05-16 11:25:18.046 coolOverlayTest[71661:7903] in drawMapRect ...theRect is -200704.000000, 37888.000000, size of 262144.000000 x 262144.000000
2011-05-16 11:25:18.048 coolOverlayTest[71661:760b] in drawMapRect ...theRect is 61440.000000, -224256.000000, size of 262144.000000 x 262144.000000
2011-05-16 11:25:18.052 coolOverlayTest[71661:760b] in drawMapRect ...theRect is 323584.000000, -224256.000000, size of 262144.000000 x 262144.000000
2011-05-16 11:25:18.054 coolOverlayTest[71661:7903] in drawMapRect ...theRect is 323584.000000, -224256.000000, size of 262144.000000 x 262144.000000
2011-05-16 11:25:18.056 coolOverlayTest[71661:760b] in drawMapRect ...theRect is -200704.000000, -224256.000000, size of 262144.000000 x 262144.000000
2011-05-16 11:25:18.057 coolOverlayTest[71661:7903] in drawMapRect ...theRect is -200704.000000, -224256.000000, size of 262144.000000 x 262144.000000
2011-05-16 11:25:18.059 coolOverlayTest[71661:760b] in drawMapRect ...theRect is 61440.000000, 300032.000000, size of 262144.000000 x 262144.000000
2011-05-16 11:25:18.061 coolOverlayTest[71661:7903] in drawMapRect ...theRect is 61440.000000, 300032.000000, size of 262144.000000 x 262144.000000
2011-05-16 11:25:18.063 coolOverlayTest[71661:760b] in drawMapRect ...theRect is 323584.000000, 300032.000000, size of 262144.000000 x 262144.000000
2011-05-16 11:25:18.064 coolOverlayTest[71661:7903] in drawMapRect ...theRect is 323584.000000, 300032.000000, size of 262144.000000 x 262144.000000
2011-05-16 11:25:18.066 coolOverlayTest[71661:760b] in drawMapRect ...theRect is -200704.000000, 300032.000000, size of 262144.000000 x 262144.000000
2011-05-16 11:25:18.068 coolOverlayTest[71661:7903] in drawMapRect ...theRect is -200704.000000, 300032.000000, size of 262144.000000 x 262144.000000
2011-05-16 11:25:18.070 coolOverlayTest[71661:760b] in drawMapRect ...theRect is 585728.000000, 37888.000000, size of 262144.000000 x 262144.000000
2011-05-16 11:25:18.072 coolOverlayTest[71661:7903] in drawMapRect ...theRect is 585728.000000, 37888.000000, size of 262144.000000 x 262144.000000
2011-05-16 11:25:18.074 coolOverlayTest[71661:760b] in drawMapRect ...theRect is -462848.000000, 37888.000000, size of 262144.000000 x 262144.000000
2011-05-16 11:25:18.075 coolOverlayTest[71661:7903] in drawMapRect ...theRect is -462848.000000, 37888.000000, size of 262144.000000 x 262144.000000
2011-05-16 11:25:18.082 coolOverlayTest[71661:7903] in drawMapRect ...theRect is 61440.000000, -486400.000000, size of 262144.000000 x 262144.000000
2011-05-16 11:25:18.082 coolOverlayTest[71661:760b] in drawMapRect ...theRect is 585728.000000, -224256.000000, size of 262144.000000 x 262144.000000
2011-05-16 11:25:18.085 coolOverlayTest[71661:760b] in drawMapRect ...theRect is 61440.000000, -486400.000000, size of 262144.000000 x 262144.000000
2011-05-16 11:25:18.087 coolOverlayTest[71661:7903] in drawMapRect ...theRect is -462848.000000, -224256.000000, size of 262144.000000 x 262144.000000
2011-05-16 11:25:18.089 coolOverlayTest[71661:760b] in drawMapRect ...theRect is -462848.000000, -224256.000000, size of 262144.000000 x 262144.000000
2011-05-16 11:25:18.099 coolOverlayTest[71661:760b] in drawMapRect ...theRect is 585728.000000, 300032.000000, size of 262144.000000 x 262144.000000
2011-05-16 11:25:18.102 coolOverlayTest[71661:760b] in drawMapRect ...theRect is -462848.000000, 300032.000000, size of 262144.000000 x 262144.000000
2011-05-16 11:25:18.106 coolOverlayTest[71661:760b] in drawMapRect ...theRect is 323584.000000, -486400.000000, size of 262144.000000 x 262144.000000
2011-05-16 11:25:18.109 coolOverlayTest[71661:760b] in drawMapRect ...theRect is -200704.000000, -486400.000000, size of 262144.000000 x 262144.000000
2011-05-16 11:25:18.111 coolOverlayTest[71661:7903] in drawMapRect ...theRect is -200704.000000, -486400.000000, size of 262144.000000 x 262144.000000
2011-05-16 11:25:18.116 coolOverlayTest[71661:760b] in drawMapRect ...theRect is 585728.000000, -486400.000000, size of 262144.000000 x 262144.000000
2011-05-16 11:25:18.119 coolOverlayTest[71661:7903] in drawMapRect ...theRect is 585728.000000, -486400.000000, size of 262144.000000 x 262144.000000
2011-05-16 11:25:18.124 coolOverlayTest[71661:7903] in drawMapRect ...theRect is -462848.000000, -486400.000000, size of 262144.000000 x 262144.000000
2011-05-16 11:25:18.126 coolOverlayTest[71661:760b] in drawMapRect ...theRect is -462848.000000, -486400.000000, size of 262144.000000 x 262144.000000
回答1:
One thing to consider is that for performance reasons, drawMapRect: is called on multiple threads. This explains why you see drawMapRect: getting called multiple times. Additionally the mapRect input to this method is NOT necessarily equal to the visible mapView.visibleMapRect. In fact mapRect is usually a small section of mapView.visibleMapRect and different threads render different regions of mapView.visibleMapRect. Thus just because a point is contained inside mapView.visibleMapRect it does not mean that it is contained within the mapRect passed to all of the resulting calls to drawMapRect.
回答2:
Problem is with setting of the line width. In your example the width is not set. If you still want to solve this problem, look here Custom MKOverlayView line width.
回答3:
You have the wrong coordinates in your call to CGContextAddLineToPoint. You have:
CGContextMoveToPoint(context, theRect.origin.x, theRect.origin.y);
CGContextAddLineToPoint(context, theRect.size.width, theRect.size.width);
but it should be:
CGContextMoveToPoint(context, theRect.origin.x, theRect.origin.y);
CGContextAddLineToPoint(context, theRect.origin.x + theRect.size.width, theRect.origin.y + theRect.size.height);
At least if you are hoping to draw a line diagonally across your rectangle.
Also as Ludvik Polak mentioned above, you probably also need to set the line width using something like:
CGContextSetLineWidth(context, MKRoadWidthAtZoomScale(zoomScale));
来源：https://stackoverflow.com/questions/6023904/ios-mkoverlayview-custom-view-rect-fills-works-but-line-draws-do-not