Create Graphics Layer

Question

I am sorry for the stupid question...I am trying to get back to this and cant even remember how to create a nd populate a graphics layer.
I cant remember what to do in VB....do I need a Query?  Or can I simply assign the Grpahics layer to a MapService and index?

I trry the below adn I am getting a failed query...I knwo this is so easy...I am drawign a complete blank

XAML:
     <esri:GraphicsLayer ID="GraphicsLayer_TrafficCameras" MouseEnter="ReturnCamera"/>

VB:
    Private Sub ClickMe(ByVal sender As System.Object, ByVal e As ESRI.ArcGIS.Client.Map.MouseEventArgs)
        Dim queryTrafficCameras As New QueryTask("http://gis.org/arcgis/rest/services/Test/MapServer/20")
        AddHandler queryTrafficCameras.ExecuteCompleted, AddressOf QueryTaskTrafficCameras_Execute
        AddHandler queryTrafficCameras.Failed, AddressOf QueryTaskTrafficCameras_Failed
        Dim query As New ESRI.ArcGIS.Client.Tasks.Query()
        query.OutFields.Add("*")
        query.ReturnGeometry = True
        queryTrafficCameras.ExecuteAsync(query)
    End Sub

Private Sub QueryTaskTrafficCameras_Execute(ByVal sender As Object, ByVal args As ESRI.ArcGIS.Client.Tasks.QueryEventArgs)
        ' Set the Target Graphics Layer
        Dim l_Cameras As GraphicsLayer = TryCast(Me.MyMap.Layers("GraphicsLayer_TrafficCameras"), GraphicsLayer)
        ' Clear previous results
        l_Cameras.ClearGraphics()

' Check for new results 
        Dim featureSet As FeatureSet = args.FeatureSet

' Get a feature count retunred from the Query and shwo that in a messagebox
        Dim Test As String = featureSet.Features.Count

If featureSet.Features.Count > 0 Then
            ' Add results to map
            For Each resultFeature As Graphic In featureSet.Features
                resultFeature.Symbol = TryCast(LayoutRoot.Resources("StrobeMarkerSymbol_Red"), ESRI.ArcGIS.Client.Symbols.Symbol)
                l_Cameras.Graphics.Add(resultFeature)
            Next
        Else
            MessageBox.Show("No features found")
        End If
    End Sub

Private Sub QueryTaskTrafficCameras_Failed(ByVal sender As Object, ByVal args As TaskFailedEventArgs)
        MessageBox.Show("Query failed: " & Convert.ToString(args.[Error]))
    End Sub

JayKappy · Answer

THanks....tried that and still nothing so looked on and it turns out I needed the where clause and an output spatial reference.

query.Where = "1=1"
        query.OutSpatialReference = MyMap.SpatialReference

Everything works now....thanks....actually took a day or two to get back into this....have been away from it for a some time....

THANKS for your thoughts and help...very appreciated.

DominiqueBroux · Answer

I figure if I was missing a reference or an Import it would tell me...I dont even get into the "AddHandler queryTrafficCameras.ExecuteCompleted, AddressOf QueryTaskTrafficCameras_Execute" ?

You are not going into the 'ExecuteCompleted' handler since your query failed (i.e you are going to your QueryTaskTrafficCameras_Failed handler). That's normal.
 Error: Is now firing into the "QueryTaskTrafficCameras_Failed" giving this error
Query failed: ESRI.ArcGIS.Client.Tasks.ServiceException

So now the question is why does your query fail?
 
My feeling is that you need to add at least one search criteria else the rest end point doesn't accept the query.
You can try by adding a dummy where clause : query.Where="1=1";
 
If still not working, use fiddler to look at the requests sent to the server, that may give a clue.

JayKappy · Answer

Very confused...if I do it as a feature layer is draws fine....so I know I can get to the data, know that its a point, know that the FeatureSymbol works fine...

Why am I erroring out?  The query seems pretty straight forward...syntax?  I figure if I was missing a reference or an Import it would tell me...I dont even get into the "AddHandler queryTrafficCameras.ExecuteCompleted, AddressOf QueryTaskTrafficCameras_Execute" ?

Anyone have any ideas?