WebPart Connections on Sharepoint. - Which Type to use?

Question

I Wrote a sample webpart which takes the parameter passed from orher webpart and display its value on a label. Here is the code:

[Guid("11a885e9-13e1-4c6e-8045-e5575794ebd8")]
public class DisplayParameter : System.Web.UI.WebControls.WebParts.WebPart
{
 protected Label _label = new Label();
    private string _message; 

 [ConnectionConsumer("Parameter to show")]
 public void GetWPConnectedProviderInterface(IWebPartField connectProvider)
 {
  FieldCallback callback = FieldCallback;
  connectProvider.GetFieldValue(callback);
 }

 private void FieldCallback(object fieldValue)
 {
  _message = (string)fieldValue;
 }

 protected override void OnPreRender(EventArgs args)
 {
  if (string.IsNullOrEmpty(_message))
   _label.Text = "No Message.";
  else
   _label.Text = _message;
 }

    protected override void CreateChildControls()
    {
        base.CreateChildControls();
  Controls.Add(_label);
    }
}

Then I put the WP on a page and a DataView WP generated with SPD, in order to pass a file name from a Doc library to the WP.
It works ok the first time, but when I select another document, I get the following Exception:

Unable to cast object of type 'Test.Assembly.SharepointProject.DislayParameter' to type 'Microsoft.SharePoint.WebPartPages.WebPart'.

This makes me think ... Do I have to inherit from Microsoft.SharePoint.WebPartPages.WebPart instead of System.Web.UI.WebControls.WebParts.WebPart?, and if so, What are the drawbacks of this, since MSDN and bloggers suggest to use the latter class?

Answer 1

I've never really agreed with not using the SharePoint-specific subclass of webpart - The only reason against it would be allowing the web part to run in containers other than SharePoint - that's nice in theory, but I have never worked on a project where there was the slightest chance the web part would be used outside SharePoint.

The issue may also be a bit clouded by the existence of a different sort of web part in SharePoint 2003 which predates .NET 2.0 web parts - that's the one that definitely shouldn't be used.