MKMapView crashes app when view controller popped

Question

I have a view controller with an MKMapView that calls

[self.mapView setRegion:region animated:YES]; 

which repositions the map from A to B.

The view controller which holds the MKMapView is set as the delegate and in

- (void)mapView:(MKMapView *)mapView regionDidChangeAnimated:(BOOL)animated

I have some code that will trigger another setRegion:animated: to the MKMapView so that the map will zoom in on the new position automatically.

Everything works fine if I popViewControllerAnimated: the view controller AFTER the MKMapView animation is done panning and zooming.

However, when I try to popViewControllerAnimated: the current view controller WHILE the MKMapView is running it's animation, the app crashes with "message sent to deallocated instance".

From the looks of the debugger, I think that MKMapView is trying to call a method from a popped and deallocated delegate.

So I tried

[self.mapView setDelegate:nil];
self.mapView = nil;

in viewDidUnload with no luck. The app still crashes consistently.

The only thing I could think of was to create a separate new delegate class and retain that class from the parent view controller so that the MKMapView would have a delegate to call even after the view controller that contains it is deallocated.

Why is this happening? Are there any other "clean" options?

Disburse

This is interesting. Our app is being crippled by baffling crashes that occur when an MKMapView calls the delegate to get a view for an annotation. The problem is that there IS no MKMapView in existence at that point; or there shouldn't be. The controller containing it has long since been popped. Wonder if it's the same problem. – Noumenon

Looks like the same problem as this: #2188598 – Noumenon

Answer 1

A friend helped me get this one.

I implemented my own method for popping the view controller instead of using the default navigation controller's back button. I just had to add [self.mapView setDelegate:nil]; before I popped the view controller.

- (void)goBack
{
    [self.mapView setDelegate:nil];
    [self.navigationController popViewControllerAnimated:YES];
}

Disburse

It wasn't possible to do this in viewWillDisappear? – Noumenon

@Oscar: I was just about to take Jiho's answer then saw your your suggestion. Should work if done in viewWillDisapear. – Math

Answer 2

OK, this is the real answer. It's from the Apple doc, but it's missing from MKMapView. It's only found under the documentation for its delegate protocol:

"Before releasing an MKMapView object for which you have set a delegate, remember to set that object’s delegate property to nil. One place you can do this is in the dealloc method where you dispose of the map view."

NOTE: This also applies to UIWebView.

I set the MapView's delegate pointer to nil in the delegate's dealloc method, and our crashes seem to have been eliminated.

Noumenon

This applies to any object which may live longer than its delegate. – Emergence

Answer 3

My problem was not solved by setting delegate of MKMapView to nil in my view Controller

[self.mapView setDelegate:nil];

I had to make a __strong reference of my UIViewController containing MKMapView in my RootViewController.

__strong <#UIViewController#> *vcNewLocation;

Sweyn

Answer 4

I had done Clustering and was marking the Annotation selected like so mapView.selectAnnotation(annotation, animated: true).

while popping, the deinit method used to crash.

So on press of back button I just add this line mapView.deselectAnnotation(selectedAnnotation, animated: false) and it solved the crash.

Fuselage

Answer 5

The following code is likely to asolve your problem:

-(void) viewWillDisappear:(BOOL)animated
{
    self.mapView.delegate = nil;
    mapView=Nil;
    NSLog(@"viewWillDisappear");

}

Krick

You forgot to call super method of viewWillDisappear:animated – Barrettbarrette