Callback after animating to a new MKMapCamera - ios

Question

I want to call a method after an MKMapView animates to a new MKMapCamera.
I started out by attaching the MKMapCamera using this method:
[self.map setCamera:cam animated:YES];
This method causes the animation but doesn't inform me when the animation finished.
I then tried implementing a callback method by using UIView animation blocks after seeing this SO post:
MKMapCamera *cam = [[MKMapCamera alloc] init];
cam.pitch = 75;
cam.altitude = 125;
[cam setCenterCoordinate:self.location.coordinate];
[UIView animateWithDuration:3.0f animations:^{
self.map.camera = cam;
} completion:^(BOOL finished) {
[self methodToImplement];
}];
The MKMapView still animates, however the methodToImplement is called at the same time.
Thanks!

Answer 1

It appears that the completion handler isn't working right for that case, so you'll need to use the MKMapViewDelegate method for region did change. See WWDC 2013 - Putting Map Kit in Perspective:
Okay now that I fired off this animation to go to the next camera I need to know when that animation completes so that I can then animate to the next camera in our stack.
Well you might think of using the completion handler here but it's going to trip you up.
I know it will.
Don't use that completion handler.
Instead you need to use MKMapViews delegate method which tells you when a region change is completed.
If you're not going to use a lot of different kind of animations, then you'll might be ok with simply using the mapView:regionDidChangeAnimated: method and checking the animated flag to call your 'methodToImplement' (the animated flag will only be true for region change that was due to animation calls, and not user input like dragging the map).
In my own project I have a more complex flow, so I needed a more flexible solution, so I opted to adding an NSMutableArray of NSBlockOperation objects as a property in my view controller containing the MKMapView. Each block operation corresponding to a would be completion handler that we can't use.
In mapView:regionDidChangeAnimated: I just pop the operations one by one and execute them:
- (void)mapView:(MKMapView *)mapView regionDidChangeAnimated:(BOOL)animated {
if (animated) {
dispatch_async(dispatch_get_main_queue(), ^{
while (self.mapRegionAnimationBlocks.count > 0) {
NSBlockOperation* op = [self.mapRegionAnimationBlocks firstObject];
[self.mapRegionAnimationBlocks removeObjectAtIndex:0];
[op start];
}
});
});
and where ever I want to use a completion handler for that block, I just add to that array before calling the animation code:
dispatch_async(dispatch_get_main_queue(), ^{
NSBlockOperation* op = [NSBlockOperation blockOperationWithBlock:^{
[self methodToImplement];
}];
[self.mapRegionAnimationBlocks addObject:op];
});
[UIView animateWithDuration:3.0f animations:^{
self.map.camera = cam;
} completion:NULL];
Note that it's important to use NSMutableArray only from a single thread (e.g. the main thread), because it's not thread-safe.
My solution is a bit of hack, and one which should probably be wrapped in a category or subclass of MKMapView, but I haven't gotten around to that yet.

Answer 2

If you set your map view's delegate, you can then write a mapViewDidFinishLoadingMap:, which "Tells the delegate that the specified map view successfully loaded the needed map data."
- (void)mapViewDidFinishLoadingMap:(MKMapView *)mapView
{
// do whatever you want
}
If you want to know not only when the map data is loaded, but also when the rendering of the map is complete (in iOS7+), you can use mapViewDidFinishRenderingMap, which "Tells the delegate that the map view has finished rendering all visible tiles."
- (void)mapViewDidFinishRenderingMap:(MKMapView *)mapView fullyRendered:(BOOL)fullyRendered
{
// do whatever you want
}
For more information, see MKMapViewDelegate Protocol Reference.