Sharepoint 2010 custom fields xml <PropertySchema>

Question

lately I have been trying to develop a custom field (cascading dropdown) for sharepoint 2010. I am using the sample from codeplex. the problem is that the sample is for sharepoint 2007 and uses the as follows in XML.

 <PropertySchema>
  <Fields>
    <Field Name="SiteUrl" Hidden="TRUE" DisplayName="SiteUrl" MaxLength="500" DisplaySize="100" Type="Text">
    </Field>

for some reason in Sharepoint 2010 this seems not to be working and is giving the following error:

System.InvalidCastException: Unable to cast object of type 'ASP._controltemplates_cascadingdropdowneditfieldcontrol_ascx' to type 'Microsoft.SharePoint.WebControls.IFieldEditor'.
at Microsoft.SharePoint.ApplicationPages.FieldCustomizationPage.CreateChildControls()
at Microsoft.SharePoint.ApplicationPages.FieldNewPage.CreateChildControls()
at System.Web.UI.Control.EnsureChildControls()
at Microsoft.SharePoint.ApplicationPages.FieldCustomizationPage.OnLoad(EventArgs e)
at Microsoft.SharePoint.ApplicationPages.FieldNewPage.OnLoad(EventArgs e)
at System.Web.UI.Control.LoadRecursive()
at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)

is there a way to add same things in CreateChildControl instead of PropertySchema?? or anyone has suggestions to solve this issue?

Answer 1

Found this site which did the cascading drop down very easily: please refer to http://www.sharepointkings.com/2010/09/sharepoint-cascading-drop-downs-using.html

Answer 2

This error may occure if your custom editor control 'ASP._controltemplates_cascadingdropdowneditfieldcontrol_ascx does not implement IFieldEditor interface or doing it wrong. MSDN recommends to use custom editor controls. Here is another greate example to start with. Hope it helps!