Getting the error "Expression does not produce a value

Question

I am relatively new to using visual basic and I am having a problem populating a list box from a database. The error that comes up is Expression does not produce a value.

Here is the code from My form:

Private Sub frmMain_Load(sender As Object, e As EventArgs) Handles MyBase.Load
    'Populate Blu Ray and DVD listboxes

    Dim objMovies As New clsMovies

    objMovies.Select_BR_List()
    objMovies.Select_Dvd_List()

    For Each strBluRay As String In objMovies.Select_BR_List
        lstBluRay.Items.Add(strBluRay)
    Next

    For Each strDVD As String In objMovies.Select_Dvd_List
        lstDvd.Items.Add(strDVD)
    Next
End Sub

And here's the code from the class:

Public Sub Select_Dvd_List()
    Dim objConnection As New SqlCeConnection(mstrCN)

    'Create SQL statement
    mstrSQL = "Select * from Dvd"
    'Instantiate command
    Dim objCommand As New SqlCeCommand(mstrSQL, objConnection)

    'open Database
    objCommand.Connection.Open()

    'Instantiate Data Reader
    Dim objDataReader As SqlCeDataReader

    'Execute SQL
    objDataReader = objCommand.ExecuteReader()

    'read Sql results
    Do While (objDataReader.Read)
        mlstDvd.Add(objDataReader.Item("dvdTitle").ToString)
    Loop

    'Close 
    objCommand.Dispose()
    objDataReader.Close()
    objDataReader.Dispose()
    objConnection.Close()
    objConnection.Dispose()
End Sub

Answer 1

The issue is that you're trying to enumerate a Sub. In VB.NET, methods can either a Sub, which doesn't return a value, or a Function, which does return a value. Your Select_Dvd_List method is a Sub, so it doesn't return a value. You have this code though:

For Each strDVD As String In objMovies.Select_Dvd_List

That is trying to loop through the result of Select_Dvd_List but, as we've already established, Select_Dvd_List has no result. In that method, you are adding items to mlstDvd so surely that loop should be:

For Each strDVD As String In objMovies.mlstDvd