Avoid flicker when moving annotations in a MKMapView on iPhone

Question

As far as I know, there isn't a way to move an annotation without removing & re-adding it to the MapView (Maybe I'm wrong).

Is there a way to prevent the MapView from being re-drawn between removing & re-adding the annotation? Right now the re-draw after removing the annotation causes a frame without the annotation, so it appears to flicker.

I need a solution that works in iOS 3.1 updates.

Thanks

capikaw capikaw · Accepted Answer · 2011-03-13T19:22:27

I figured out how achieve flicker free annotation "updates" using the below code. In a nut shell, you add your new pin FIRST, then delete the old one AFTER. I haven't streamlined my code yet but you'll get the idea.

-(void)replacePin:(NSString *)title SubTitle:(NSString *)subTitle Location:(CLLocationCoordinate2D)location PinType:(MapAnnotationType)pinType Loading:(BOOL)loading Progress:(float)progress
{
    //Find and "decommission" the old pin... (basically flags it for deletion later)
    for (MyMapAnnotation *annotation in map.annotations) 
    {
        if (![annotation isKindOfClass:[MKUserLocation class]])
        {
            if ([annotation.title isEqualToString:title])
                annotation.decommissioned = YES;
        }
    }

    //add the new pin...
    MyMapAnnotation *stationPin = nil;
    stationPin = [[MyMapAnnotation alloc] initWithCoordinate:Location
                                              annotationType:pinType
                                                       title:title
                                                    subtitle:subTitle
                                                     loading:loading
                                              decommissioned:NO
                                                    progress:progress];
    [map addAnnotation:stationPin];
    [stationPin release];
}

Then AFTER, I make the call to search for and remove any decommissioned pins:

- (MKAnnotationView *)mapView:(MKMapView *)mapView viewForAnnotation:(id <MKAnnotation>)annotation
{
    MKAnnotationView* annotationView = nil;

    if (![annotation isKindOfClass:[MKUserLocation class]])
    {
        MyMapAnnotation* annotation = (MyMapAnnotation*)annotation;

        //your own details...

        //delete any decommissioned pins...
        [self performSelectorOnMainThread:@selector(deletePin:) withObject:annotation.title waitUntilDone:NO];
    }
    return annotationView;

}

And finally, in the background get rid of the old pin:

-(void)deletePin:(NSString *)stationCode
{
    for (MyMapAnnotation *annotation in map.annotations) 
    {
        if (![annotation isKindOfClass:[MKUserLocation class]])
        {
            if ([annotation.title isEqualToString:stationCode])
            {  
                if (annotation.decommissioned)
                    [map removeAnnotation:annotation];
            }
        }
    }
}

Avoid flicker when moving annotations in a MKMapView on iPhone

3 Answers