Subclassing MKOVerlay View- canDrawMapRect not called

问题

I am attempting to subclass MKOverlayView to create a custom overlay. I understand that in order to do this, one must override the following two methods

- (void)drawMapRect:(MKMapRect)mapRect zoomScale:(MKZoomScale)zoomScale inContext:(CGContextRef)context;

- (BOOL)canDrawMapRect:(MKMapRect)mapRect zoomScale:(MKZoomScale)zoomScale;

My question arrises from the latter method. For some reason, when I override it in my MKOverlayView subclass, it does not get called. According to documentation, it should be called before tiles are rendered and if it returns YES, then drawMapRect is called. I was hoping that someone could look at the following code and see if they can figure out why this method is not being called. Is it meant to be enabled/called manually somewhere?

Interestingly enough, drawMapRect does get called, it's only canDrawMapRect that does not. Am I misinterpreting the functionality of canDrawMapRect or is something wrong in my code?

HeatMapOverlay.h

#import <MapKit/MapKit.h>
#import <Foundation/Foundation.h>
@interface HeatMapOverlayView : MKOverlayView{
    ...variables...
}

@end

HeatMapOverlay.m

#import "HeatMapOverlayView.h"
#import <CoreGraphics/CoreGraphics.h>
#import <QuartzCore/QuartzCore.h>

@implementation HeatMapOverlayView
@synthesize points, heat, QualityIndex;
- (id)initWithOverlay:(id<MKOverlay>)overlay {
    self = [super init];
    if (self) {
        // Initialization code here.
    }
    return self;
}


- (BOOL)canDrawMapRect:(MKMapRect)mapRect zoomScale:(MKZoomScale)zoomScale{
         ...complete check...
return NO;
}


- (void)drawMapRect:(MKMapRect)mapRect zoomScale:(MKZoomScale)zoomScale inContext (CGContextRef)context{
...draw overlay...
}

Thank you!

回答1:

Try changing this line:

self = [super init];

to this to use the proper initializer for an MKOverlayView:

self = [super initWithOverlay:overlay];

来源：https://stackoverflow.com/questions/6962186/subclassing-mkoverlay-view-candrawmaprect-not-called

标签

iphone

mkmapview

mkoverlay