Do I have to implement mapView:regionWillChangeAnimated:on my MKMapview delegate? - iphone

Question

Apple's docs tell you this method should be as lightweight as possible, what's a standard use here? Resetting the annotation pins?
Tells the delegate that the region
displayed by the map view is about to
change.
- (void)mapView:(MKMapView *)mapView regionWillChangeAnimated:(BOOL)animated
Parameters
mapView
The map view whose visible region is
about to change.
animated
If YES, the change to the new region
will be animated. If NO, the change
will be made immediately.
This method is called whenever the
currently displayed map region
changes. During scrolling, this method
may be called many times to report
updates to the map position.
Therefore, your implementation of this
method should be as lightweight as
possible to avoid affecting scrolling
performance.

Answer 1

The problem with this delegate method is "During scrolling, this method may be called many times to report updates to the map position" (so you need IF/THEN or CASE/BREAK, etc to keep it "lightweight").
You don't NEED to use this method at all (not required), but if you do wish to incorporate some sort of functionality (such as removing worthless pins, etc), then example code to keep it lightweight would be:
- (void)mapView:(MKMapView *)mapView regionWillChangeAnimated:(BOOL)animated{
if(!animated){
//Instantaneous change, which means you probably did something code-wise, so you should have handled anything there, but you can do it here as well.
} else {
//User is most likely scrolling, so the best way to do things here is check if the new region is significantly (by whatever standard) away from the starting region
CLLocationDistance *distance = [mapView.centerCoordinate distanceFromLocation:originalCoordinate];
if(distance > 1000){
//The map region was shifted by 1000 meters
//Remove annotations outsides the view, or whatever
//Most likely, instead of checking for a distance change, you might want to check for a change relative to the view size
}
}
}