Accepting Nullable Dates

				The .NET datetime variable data type does not accept null as a value. If you are using SQL Server, you can get around this by making your field variables SqlDateTime data type. The SqlDateTime data type implements the nullable option. 
To illustrate how to use this, 
Create a web form (VB.NET) that contains two textboxes called "txtaltstartdate" and "txtaltenddate". They can be databound to the corresponding fields in the SQL Server database.
Also add a "Save" button.
View the code
At the top of your class, put
Imports System.Data.SqlTypes
In the code behind for the "Save" button, you would place the following code:
Dim objaltstartdate As TextBox
Dim objaltenddate As TextBox
Dim sqldatenull As SqlDateTime
sqldatenull = SqlDateTime.Null
objaltstartdate = CType(e.Item.FindControl("txtaltstartdate"), TextBox)
objaltenddate = CType(e.Item.FindControl("txtaltenddate"), TextBox)
' Then, open your database connection and 
' assuming you have a stored procedure to handle 
' updates it would be processed as follows, 
' passing the value:
Dim objSQLConnection As New SqlConnection
Dim objSQLCommand As New SqlCommand
Dim strConnectString As String
strConnectString = ConfigurationSettings.AppSettings("gstrConnection")
objSQLConnection = New SqlConnection(strConnectString)
objSQLConnection.Open()
objSQLCommand = New SqlCommand("sp_update", objSQLConnection)
objSQLCommand.CommandType = CommandType.StoredProcedure
' One tricky thing is you have to use the 
' SqlDateTime.Parse option to take the string 
' value in the text box and convert it to 
' sqlDatetime.
If objaltstartdate.Text <> "" Then
objSQLCommand.Parameters.Add(New SqlParameter("@pAlternateEventStartDate", SqlDbType.DateTime))
objSQLCommand.Parameters("@pAlternateEventStartDate").Value = SqlDateTime.Parse(objaltstartdate.Text)
else
objSQLCommand.Parameters.Add(New SqlParameter("@pAlternateEventStartDate", SqlDbType.DateTime))
objSQLCommand.Parameters("@pAlternateEventStartDate").Value = sqldatenull
endif
If objaltenddate.Text <> "" Then
 objSQLCommand.Parameters.Add(New SqlParameter("@pAlternateEventEndDate", SqlDbType.DateTime))
 objSQLCommand.Parameters("@pAlternateEventEndDate").Value = SqlDateTime.Parse(objaltenddate.Text)
else
 objSQLCommand.Parameters.Add(New SqlParameter("@pAlternateEventEndDate", SqlDbType.DateTime))
 objSQLCommand.Parameters("@pAlternateEventEndDate").Value = sqldatenull
endif
objSQLCommand.ExecuteNonQuery()
objSQLCommand.Dispose()
objSQLConnection.Close()
objSQLConnection.Dispose()
objSQLCommand = Nothing
objSQLConnection = Nothing