topic Re: Layers CollectionChanged Event in ArcGIS API for Silverlight Questions

Layers CollectionChanged Event

MatthewPilgrim — Mon, 08 Nov 2010 15:02:01 GMT

Hi,

The Map.Layers.CollectionChanged event is firing when I set the DrawMode on a Client.Draw object, is this correct?

I simply wanted to catch when new layers were added or removed but this event fires as the user starts drawing buffers. I looked at the event args and I can't distinguish between this event firing due to legitimate changes in hte number of layers.

Any ideas?

Matt

Re: Layers CollectionChanged Event

JenniferNery — Mon, 08 Nov 2010 17:16:31 GMT

This is correct, the Draw object, creates a new GraphicsLayer on top of your layers. Therefore Layers.CollectionChanged event will fire. You can probably ignore if the layer added has no ID to distinguish the layer you create and the layer the API creates dynamically.

Re: Layers CollectionChanged Event

MatthewPilgrim — Fri, 10 Dec 2021 22:58:18 GMT

Thank you for the response. I've added this code:

public void Layers_CollectionChanged(Object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
      {
          //this event if fired when this code is executed: MyDrawObject.DrawMode = DrawMode.... 
          //so we look for single layers being added/removed with null Ids
          //we supress the refresh in these circumstances

          bool DontFire = false;
         
          if (e.Action == System.Collections.Specialized.NotifyCollectionChangedAction.Add)
          {
              if (e.NewItems != null  && e.NewItems.Count == 1)
              {
                  if (((ESRI.ArcGIS.Client.Layer)e.NewItems[0]).ID == null)
                  {
                      DontFire = true;
                  }
              }
          }
          else if (e.Action == System.Collections.Specialized.NotifyCollectionChangedAction.Remove)
          {
              if (e.OldItems != null && e.OldItems.Count == 1)
              {
                  if (((ESRI.ArcGIS.Client.Layer)e.OldItems[0]).ID == null)
                  {
                      DontFire = true;
                  }
              }
          }

          if (DontFire == false)
          {
              Refresh();
          }
       }

Hopefully that will do the job.

Re: Layers CollectionChanged Event

JenniferNery — Tue, 09 Nov 2010 16:30:02 GMT

Yup I think that should work.

Another suggestion is that you can use

!string.IsNullOrEmpty(layer.ID)