ESRI Silverlight API: Defining Unique Value Renderer in XAML

I’ve been creating some proof of concept applications in Silverlight, and one thing I needed to do was apply a unique value renderer using PictureMarkerSymbols to some points on a FeatureLayer.

Initially I looked in the Samples and Reference sections of the ESRI Silverlight Resource Center. However, I was some what stymied. The Samples had a simple example of loading a feature layer, but it used the built-in clustering. I could find all sorts of details in the API Reference, but that does not help sort out how to setup a renderer in XAML.

Finally I stumbled into the Concepts section. I had figured that this section would be some very basic stuff – but there are a number of very useful code examples in there – specifically an example creating renderers in XAML. The example is for polygons, and is pretty comprehensive, but I thought I’d share a code sample for a unique value renderer using a PictureMarkerSymbol, as this is very much akin to slapping push-pins into other map canvasses like Google Maps or Virtual Earth.

The idea is pretty simple – in the Grid.Resources section of your XAML, define a bunch of PictureMarkerSymbols with names, then create a unique value renderer, and add in unique value items, which tie the attribute value to the specific marker symbol using data binding to the symbols we just defined. Follow that? It makes more sense in XAML…

<Grid.Resources>
    <esriSymbols:PictureMarkerSymbol x:Name="HelicopterSymbol" Height="40" Width="40" Source="Assets/images/i_helicopter.png" />
    <esriSymbols:PictureMarkerSymbol x:Name="DozerSymbol" Height="40" Width="40"  Source="Assets/images/i_truck.png" />
    <esriSymbols:PictureMarkerSymbol x:Name="PumperSymbol"  Height="40" Width="40" Source="Assets/images/i_firetruck.png"/>
    <esriSymbols:PictureMarkerSymbol x:Name="JumperSymbol"  Height="40" Width="40" Source="Assets/images/i_fireman.png"/>
    <esri:UniqueValueRenderer x:Name="FireResourcesRenderer" Attribute="Type" >
        <esri:UniqueValueRenderer.Infos>
            <esri:UniqueValueInfo Value="HELO" Symbol="{StaticResource HelicopterSymbol}" />
            <esri:UniqueValueInfo Value="DOZER" Symbol="{StaticResource DozerSymbol}" />
            <esri:UniqueValueInfo Value="PUMPER" Symbol="{StaticResource PumperSymbol}" />
            <esri:UniqueValueInfo Value="JUMPER" Symbol="{StaticResource JumperSymbol}" />
        </esri:UniqueValueRenderer.Infos>
    </esri:UniqueValueRenderer>
</Grid.Resources>

Then in the FeatureLayer definition we bind the renderer property to the renderer we defined in the Grid.Resources.

<esri:FeatureLayer
       ID=”FireResources”
       Url=”http://yourserver/ArcGIS/rest/services/yourmapeservice/MapServer/0″
       Where=”1=1″
       ClusterFeatures=”False”                     
       Renderer=”{StaticResource FireResourcesRenderer}”>
    <esri:FeatureLayer.OutFields>
        <sys:String>Type</sys:String>                               
    </esri:FeatureLayer.OutFields>
</esri:FeatureLayer>

And that’s it!