To set parameter value, use DefaultValue.
EDIT : I have noticed you are using e.Command.Parameters
which wouldn't help much. Try the following:
Purchase.aspx.vb
Imports System.Collections.Generic
Imports System.Data.Common
Imports System.Linq
Partial Public Class ManageFavoritesWithUserProperty
Inherits System.Web.UI.Page
Protected Sub SqlDataSource1_Selecting(sender As Object, e As System.Web.UI.WebControls.SqlDataSourceSelectingEventArgs)
Dim param = SqlDataSource1.SelectParameters
AssignUserName(param)
End Sub
Protected Sub SqlDataSource1_Inserting(sender As Object, e As System.Web.UI.WebControls.SqlDataSourceCommandEventArgs)
Dim param = SqlDataSource1.InsertParameters
AssignUserName(param)
End Sub
Protected Sub SqlDataSource1_Updating(sender As Object, e As System.Web.UI.WebControls.SqlDataSourceCommandEventArgs)
Dim param = SqlDataSource1.UpdateParameters
AssignUserName(param)
End Sub
Protected Sub SqlDataSource1_Deleting(sender As Object, e As System.Web.UI.WebControls.SqlDataSourceCommandEventArgs)
Dim param = SqlDataSource1.DeleteParameters
AssignUserName(param)
End Sub
Private Sub AssignUserName(parameters As ParameterCollection)
parameters("@UserName").DefaultValue = User.Identity.Name
End Sub
End Class
Partial Class Members_Default
Inherits System.Web.UI.Page
End Class