Knowing.NET

Xamarin: You must explicitly unsubscribe from NSNotifications if IDisposable

In Xamarin, if you observe / subscribe to a particularly-named NSNotification in an object that is IDisposable (this includes any class descended from NSObject!), you MUST explicitly unsubscribe from it in your Dispose handler, or you will get a segfault (the system will attempt to call a method at a memory location that is no longer valid). The pattern looks like this:

class MyClass : NSObject
{
// instance variable
private NSObject notificationObservationHandle;

      MyClass()
      { 
         notificationObservationHandle = NSNotificationCenter.DefaultCenter.AddObserver(notificationName, NotificationHandler);
      }

      void NotificationHandler(NSNotification notification)
      {
         // ... etc ...
      }

      private bool disposed = false;
      override protected void Dispose(bool disposing)
      {
         if (!disposed)
         {
               if (disposing)
               {
                  NSNotificationCenter.DefaultCenter.RemoveObserver(notificationObserverHandle);
               }
               disposed = true;
               base.Dispose();
         }
      }
}