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?

Tom Clarkson Tom Clarkson · Accepted Answer · 2009-05-15T04:30:28

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.

WebPart Connections on Sharepoint. - Which Type to use?

1 Answers