How can I create a custom "pin-drop" animation using MKAnnotationView?

Question

I have an instance of MKMapView and would like to use custom annotation icons instead of the standard pin icons supplied by MKPinAnnotationView. So, I've setup a subclass of MKAnnotationView called CustomMapAnnotation and am overriding -(void)drawRect: to draw a CGImage. This works.

The trouble comes when I try to replicate the .animatesDrop functionality supplied by MKPinAnnotationView; I would love for my icons to appear gradually, dropped from above and in left-to-right order, when the annotations are added to the MKMapView instance.

Here is -(void)drawRect: for CustomMapAnnotation, which works when you just draw the UIImage (which is what the 2nd line does):

- (void)drawRect:(CGRect)rect {
 [super drawRect:rect];
 [((Incident *)self.annotation).smallIcon drawInRect:rect];
 if (newAnnotation) {
  [self animateDrop];
  newAnnotation = NO;
 }
} 

The trouble comes when you add the animateDrop method:

-(void)animateDrop {
 CGContextRef myContext = UIGraphicsGetCurrentContext();

 CGPoint finalPos = self.center;
 CGPoint startPos = CGPointMake(self.center.x, self.center.y-480.0);
 self.layer.position = startPos;

 CABasicAnimation *theAnimation;
 theAnimation=[CABasicAnimation animationWithKeyPath:@"position"];
 theAnimation.fromValue=[NSValue valueWithCGPoint:startPos];
 theAnimation.toValue=[NSValue valueWithCGPoint:finalPos];
 theAnimation.removedOnCompletion = NO;
 theAnimation.fillMode = kCAFillModeForwards;
 theAnimation.delegate = self;
 theAnimation.beginTime = 5.0 * (self.center.x/320.0);
 theAnimation.duration = 1.0;
 [self.layer addAnimation:theAnimation forKey:@""];
}

It just doesn't work, and there could be a lot of reasons why. I won't get into all of them now. The main thing I am wanting to know is if the approach is sound at all, or if I should try something entirely different.

I tried also to package up the whole thing into an animation transaction so that the beginTime parameter might actually work; this seemed to not do anything at all. I don't know if this is because I am missing some key point or whether it's because MapKit is trashing my animations somehow.

  // Does nothing
  [CATransaction begin];
  [map addAnnotations:list];
  [CATransaction commit];

If anyone has any experience with animated MKMapAnnotations like this, I'd love some hints, otherwise if you can offer CAAnimation advice on the approach, that'd be great too.

Answer 1

One problem with the code by Paul Shapiro is that it doesn't deal with when you add annotations below where the user is looking at the moment. Those annotations will float in mid-air before dropping because they are moved into the user's visible map rect.

Another is that it also drops the user location blue dot. With this code below, you handle both user location and large amounts of map annotations off-screen. I've also added a nice bounce ;)

- (void)mapView:(MKMapView *)mapView didAddAnnotationViews:(NSArray *)views {
    MKAnnotationView *aV; 

    for (aV in views) {

        // Don't pin drop if annotation is user location
        if ([aV.annotation isKindOfClass:[MKUserLocation class]]) {
            continue;
        }

        // Check if current annotation is inside visible map rect, else go to next one
        MKMapPoint point =  MKMapPointForCoordinate(aV.annotation.coordinate);
        if (!MKMapRectContainsPoint(self.mapView.visibleMapRect, point)) {
            continue;
        }

        CGRect endFrame = aV.frame;

        // Move annotation out of view
        aV.frame = CGRectMake(aV.frame.origin.x, aV.frame.origin.y - self.view.frame.size.height, aV.frame.size.width, aV.frame.size.height);

        // Animate drop
        [UIView animateWithDuration:0.5 delay:0.04*[views indexOfObject:aV] options:UIViewAnimationCurveLinear animations:^{

            aV.frame = endFrame;

        // Animate squash
        }completion:^(BOOL finished){
            if (finished) {
                [UIView animateWithDuration:0.05 animations:^{
                    aV.transform = CGAffineTransformMakeScale(1.0, 0.8);

                }completion:^(BOOL finished){
                    [UIView animateWithDuration:0.1 animations:^{
                        aV.transform = CGAffineTransformIdentity;
                    }];
                }];
            }
        }];
    }
}