Object reference not set to an instance of an object.

[mcmahon]

I need help with an error I'm getting;
"Object reference not set to an instance of an object." The error occurs at the line :

Dim intselA As Integer = CInt(lstStudents.SelectedItem.ToString)

The items in lstStudents is text. StudentID is an autonumber.
What I'm trying to do is populate a the database with all the studentID's of the names in the list box. (i.e. every name in the list box has a corresponding studentID)

Your help would be really appreciated.

Thanks

                Dim intselA As Integer = CInt(lstStudents.SelectedItem.ToString)
                Dim BRow As DataRow = objDataSet.Tables("tblStudent").Rows.Find(intselA)
                If BRow IsNot Nothing Then
                    'use the data relationship to find all matching student rows
                    Dim studentRows() As DataRow = BRow.GetChildRows("tblStudent")
                    If studentRows.Length > 0 Then
                        For Each student As DataRow In studentRows
                            Dim strID As String = student("StudentID")
                            'add this item
                            objCurrentRow1.Item("StudentID") = strID
                        Next
                    End If
                End If

[Plater]

You are not verifying that lstStudents.SelectedItem is a valid object (in vb.net you would check if it equals Nothing)

The default selected index is -1 (invalid) to note that nothing is selected in the control. This comes up when applying a datasource to the control as well as when a user de-selects all the items