topic Re: Preventing Duplicate Graphics in GraphicsLayer in ArcGIS API for Silverlight Questions

Preventing Duplicate Graphics in GraphicsLayer

JoeHamilton — Tue, 28 Dec 2010 20:25:54 GMT

Hi all...

When iterating query results, is there an easy way to detect if the feature already exists in the current graphicsLayer?

For Each feature As Graphic In e.FeatureSet.Features

                Dim graph As Graphic = feature
                Dim myAddedGraphic = (From a In graphicsLayer.Graphics Select a Where a.Equals(graph)).First()

                    If myAddedGraphic Is Nothing Then
                        graphicsLayer.Graphics.Insert(0, feature)
                    End If
                Next

This isn't working. I tried Where a IS graph, where a.Geometery.Equals(graph.Geometry) etc..

I just can't seem to use LINQ to find the item if it exists in the list. Any else get this working?

Re: Preventing Duplicate Graphics in GraphicsLayer

AliMirzabeigi — Fri, 10 Dec 2021 22:26:08 GMT

You cannot check existance of a feature on a layer against instances of the features returned by the query task, instead you should check for equality in their unique identifier attribute. Assuming you have an "ObjectID" field in your layer a sample C# code would be:

var graphic = from g in graphicsLayer.Graphics
                     where g.Attributes["ObjectID"].Equals(feature.Attributes["ObjectID"])
                     select g;
if (graphic.Count() == 0)
{
    // Code for adding the graphic here
}

Re: Preventing Duplicate Graphics in GraphicsLayer

JoeHamilton — Tue, 28 Dec 2010 22:21:19 GMT

ali5110
Thanks for the info. I'm going to have to add an attribute to the graphic that is the name of the layer I'm querying. Then I can check for uniqueness across table & objectID.

That should work great! Thanks.