topic Re: Odd FeatureLayer Implementation Behavior in ArcGIS API for Silverlight Questions

Odd FeatureLayer Implementation Behavior

DonnieHolmes — Thu, 08 Jul 2010 13:11:11 GMT

I have a need to implement the FeatureLayer class so that i can add my own DependencyProperties, events, etc. I've finally been able to get this to work, but i've noticed some odd behavior. If you:

   1. Implement the FeatureLayer class as "MyFeatureLayer" (do nothing else in the class)
   2. Add your "MyFeatureLayer" class to the map as you would a regular FeatureLayer (make all the required settings so that data should load)
   3. Notice that when you load the app the FeatureLayer never completely loads

Somehow i stumbled upon the workaround that if you set the map extent explicitly on the map itself rather than letting it pick up from the first layer that loads, everything seems to work fine.

So, am i try to do something that's not really supported, or is this a bug? I haven't upgraded to the 2.0 RC as we haven't yet upgraded our ArcGIS Server to the 10.0 release version. (currently using beta versions of both)

Re: Odd FeatureLayer Implementation Behavior

dotMorten_esri — Thu, 08 Jul 2010 15:09:46 GMT

You can still use v2.0 with an ArcGIS 9.3.1 server.

If you want to create your own featurelayer, you should
1) Inherit from GraphicsLayer
2) Internally add a querytask that populates the Graphics collection with whatever comes back from the QueryTask.

In other words, all a featurelayer is (at least at v1.x) is just a graphicslayer with a built-in querytask.

Re: Odd FeatureLayer Implementation Behavior

DonnieHolmes — Thu, 08 Jul 2010 15:37:09 GMT

Thanks for the reply Morten. Sorry, i should have been more clear about the versions we are using. We currently are running ArcGIS Server 10 (just not the final release) and we are using the 2.0 WPF/Silverlight SDK (beta).

I would like to take advantage of the editing goodness and ondemand feature loading that comes with the 2.0 FeatureLayer - which is why i chose that route rather than GraphicsLayer. Are you saying that we shouldn't attempt to inherit from FeatureLayer at all?

Re: Odd FeatureLayer Implementation Behavior

dotMorten_esri — Thu, 08 Jul 2010 22:48:42 GMT

Sorry I misunderstood. Inheriting from FeatureLayer should be fine. But you could be overriding some methods incorrectly. Are you overriding anything? (if you are make sure you call the base method as well).

Re: Odd FeatureLayer Implementation Behavior

DonnieHolmes — Sat, 11 Dec 2021 20:47:22 GMT

I finally figured out what is wrong, and it doesn't appear related to implementing the FeatureLayer class. It seems that if there is only a FeatureLayer in the map, then it won't pay any attention to it unless you explicitly set the map extent. Using data from the ESRI sample services:

This loads as expected:

<esri:Map x:Name="MyMap">
            <esri:ArcGISTiledMapServiceLayer ID="StreetMapLayer"
                    Url="http://server.arcgisonline.com/ArcGIS/rest/services/ESRI_StreetMap_World_2D/MapServer"/>
            <esri:FeatureLayer ID="MyFeatureLayer"
                    Url="http://sampleserver1.arcgisonline.com/ArcGIS/rest/services/Specialty/ESRI_StatesCitiesRivers_USA/MapServer/0"/>
</esri:Map>

Nothing loads for this scenario:

<esri:Map x:Name="MyMap">            
            <esri:FeatureLayer ID="MyFeatureLayer"
                    Url="http://sampleserver1.arcgisonline.com/ArcGIS/rest/services/Specialty/ESRI_StatesCitiesRivers_USA/MapServer/0"/>
</esri:Map>

However, this does work (which does nothing more than set the map to the extent and spatial ref of the feature layer):

<esri:Map x:Name="MyMap">
            <esri:Map.Extent>
                <esri:Envelope XMin="-158.064605712891" YMin="19.6961498260498" XMax="-67.986768734036" YMax="64.8691042579708" >
                    <esri:Envelope.SpatialReference>
                        <esri:SpatialReference WKID="4326"/>
                    </esri:Envelope.SpatialReference>
                </esri:Envelope>
            </esri:Map.Extent>
            <esri:FeatureLayer ID="MyFeatureLayer"
                    Url="http://sampleserver1.arcgisonline.com/ArcGIS/rest/services/Specialty/ESRI_StatesCitiesRivers_USA/MapServer/0"/>
        </esri:Map>

This seems like a bug to me.

Re: Odd FeatureLayer Implementation Behavior

DominiqueBroux — Sat, 11 Dec 2021 20:47:25 GMT

You are right the map extent is not initialized from the feature layer.

You can initialize the map extent in the featurelayer initialized event:

 
private void FeatureLayer_Initialized(object sender, System.EventArgs e)
{
FeatureLayer featureLayer = sender as FeatureLayer;
MyMap.Extent = featureLayer.LayerInfo.Extent;
}

Re: Odd FeatureLayer Implementation Behavior

DonnieHolmes — Mon, 12 Jul 2010 14:25:13 GMT

Thanks Dominique. Is this behavior by design? I'm just curious as to why the map would ignore feature layers for its extent and spatial reference info.