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我正在使用 iOS 7 并扩展了 MKOverlayPathRenderer，以便在 MKMap 上绘制自定义叠加层。

我已经实现了 MKOverlayPathRenderer 类的以下方法，并且 NSLog 输出显示当我期望时调用代码来绘制上下文。但是，自定义叠加层根本不会显示在地图上。

---CustomPathRenderer extends MKOverlayPathRenderer----

    -(void)drawMapRect:(MKMapRect)mapRect zoomScale:(MKZoomScale)zoomScale inContext:(CGContextRef)ctx
        {

            CGContextSetAlpha(ctx, 0.9);

            if([self.overlay isKindOfClass:[CustomPathOverlay class]]){

                CustomPathOverlay *path = (CustomPathOverlay *)self.overlay;

                for(int idx = 1; idx < path.selected.positions.count; idx++)
                {
                    CGContextBeginPath(ctx);

                    Position* firstPosition = (Position *)[path.selected.positions objectAtIndex:idx-1];

                    CGPoint firstpoint = [self.mapView convertCoordinate:firstPosition.location toPointToView:self.mapView];

                    CGContextMoveToPoint(ctx, firstpoint.x , firstpoint.y);

                    Position* pos = (Position *)[flightPath.selectedAircraft.positions objectAtIndex:idx];

                    CGPoint point = [self.mapView convertCoordinate:pos.location toPointToView:self.mapView];

                    NSLog(@"Drawing X:%f Y:%f",point.x,point.y);

                    CGContextAddLineToPoint(ctx, point.x, point.y);

                    CGContextSetStrokeColorWithColor(ctx,[UIColor redColor].CGColor);<-- THIS WILL BECOME A FUNCTION OF A POSITION PROPERTY RATHER THAN JUST RED.

                    CGContextSetLineWidth(ctx, 0.5 * MKRoadWidthAtZoomScale(zoomScale));

                    CGContextStrokePath(ctx);
                }

                // Last segment to the last known position.
                CGContextBeginPath(ctx);

                Position* lastPosition = (Position *)[path.selected.positions lastObject];

                CGPoint lastPoint = [_mapView convertCoordinate:lastPosition.location toPointToView:self.mapView];

                CGContextMoveToPoint(ctx, lastPoint.x , lastPoint.y);

                Position *estimatedPosition = [path.selected.position estimatePosition];

                CGPoint endPoint = [self.mapView convertCoordinate:estimatedPosition.location toPointToView:self.mapView];

                CGContextAddLineToPoint(ctx, endPoint.x, endPoint.y);

                CGContextSetStrokeColorWithColor(ctx,[UIColor redColor].CGColor); 

                CGContextSetLineWidth(ctx, 0.5 * MKRoadWidthAtZoomScale(zoomScale));

                CGContextStrokePath(ctx);


            }

    }

这是(MKOverlayRenderer *)mapView:(MKMapView *)mapView rendererForOverlay:(id < MKOverlay >)overlay我的 MKMapViewDelegate 方法中的代码：

    - (MKOverlayRenderer *)mapView:(MKMapView *)mapView rendererForOverlay:(id < MKOverlay >)overlay
{

    if([overlay isKindOfClass:[CustomPathOverlay class]]){
        CustomPathRenderer *renderer = [[CustomPathRenderer alloc]initWithOverlay:overlay andMapView:mapView];

        return renderer;
    }

    return nil;

}

我真的很感激一些关于为什么这可能不会在 MKMapView 上呈现的线索。

非常感谢

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