ActiveMapViewChangedEvent

Question

Hi, I'm trying to detect when the current MapView changes, so I can then activate/deactivate a button on a toolbar based on layers in the active map. But when I click on (for example) the 'Catalog' tab, the ActiveMapViewChangedEvent fires and I get a NullReferenceException. As a workaround, I just catch the exception and disable the tool. Is there a better way to determine if the user is no longer on a 'MapView' tab?? ActiveMapViewChangedEvent.Subscribe((args) => { try { var lyr = MapView.Active.Map.FindLayers("SDEDB1.GISADMIN.ADDR_Durham").FirstOrDefault(); if (lyr == null) FrameworkApplication.State.Deactivate(StateID); else FrameworkApplication.State.Activate(StateID); } catch (NullReferenceException) { FrameworkApplication.State.Deactivate(StateID); } });‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

BrianBulla · Answer

Great....thanks Uma and Narelle for your help.  Both methods work as I need them to.

NarelleChedzey · Answer

Brian,

In addition you should never assume that there is always a mapview active.  What if your user has a layout active?   What if your user has no mapviews open.   In both of these scenarios, MapView.Active will be null  and MapView.Active.Map will throw a nullReferenceException as you are experiencing.

Rather than wrap in a try, catch.  you should add the following to your code

if (MapView.Active == null) return;

UmaHarano · Answer

Hi Brian When the ActiveMapViewChanged event fires, you can check the Event args to see if the "IncomingView" arg is null. Like this code snippet: ActiveMapViewChangedEvent.Subscribe(OnActiveMapViewChanged); private async void OnActiveMapViewChanged (ActiveMapViewChangedEventArgs activeMapViewChangedEventArgs) { if (activeMapViewChangedEventArgs.IncomingView == null) return; .... }‍‍‍‍‍‍‍‍‍