topic Re: ActiveMapViewChangedEvent in ArcGIS Pro SDK Questions

ActiveMapViewChangedEvent

BrianBulla — Sun, 12 Dec 2021 11:06:54 GMT

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);
                }                
            });‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

Re: ActiveMapViewChangedEvent

UmaHarano — Sun, 12 Dec 2021 11:06:56 GMT

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;
      ....
   }‍‍‍‍‍‍‍‍‍

Re: ActiveMapViewChangedEvent

NarelleChedzey — Thu, 12 Apr 2018 16:29:02 GMT

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;

Re: ActiveMapViewChangedEvent

BrianBulla — Thu, 12 Apr 2018 17:04:03 GMT

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