Trying to speed up GUI response time - Combobox SelectIndexValue event slows down app
 

I realize that the response time of my GUI is extremely slow! I have three combo boxes - I want the user to select a template from one drop down list, which will populate the second drop down list with customers related to that template. When a customer is selected, the third drop down list is to be populated with items related to that customer.

Each code snippet that selects the next level (template -> customer; customer -> item) is stored in a separate procedure:

 Private Sub SelectTemplate()

        'User selects the template desired from the drop down list

        Try

            Select Case cboTemplate.Text

                Case Is = "South"

                    SQL_Text = "SELECT itemno, [item desc], barcode, cat, baseunit, stockunit FROM SBI_SOUTH_CUST_ITEMS"

            End Select

            RegionString = SQL_Text

        Catch ex As Exception

            MessageBox.Show("Error:" & ex.Message, "Error", MessageBoxButtons.OK, MessageBoxIcon.Error)

        End Try

    End Sub

 Private Sub PopulateCustList()

        'Shows list of customers in Customers drop down list

        Dim SelectCust As String

        Try

            SelectCust = "SELECT * FROM OTM_SOUTH_CUSTOMERS"

            Dim SQLCom As New SqlCommand(SelectCust, SQLCon)

            da = New SqlDataAdapter(SelectCust, SQLCon)

            da.Fill(Custds, "cust")



            CustomerLoading = True 'Set flag on

            cboCustomer.DataSource = Custds.Tables("cust")

            cboCustomer.DisplayMember = "name"

            CustomerLoading = False 'Set flag off



        Catch ex As Exception

            MessageBox.Show("Error:" & ex.Message, "Error", MessageBoxButtons.OK, MessageBoxIcon.Error)

        End Try

Private Sub ShowCustomerDetails()

        'Show items details for specific customers in Items drop down list

        Dim da As SqlDataAdapter

        Dim dt As New DataSet



        Try

            Dim SQLCom As New SqlCommand(SQL_Text, SQLCon)

            da = New SqlDataAdapter(SQL_Text, SQLCon)

            da.Fill(dt, "details")

            dgView.DataSource = dt.Tables("details")

            dgView.AutoResizeColumns()

            ItemLoading = True

            cboItem.DataSource = dt.Tables(0)

            cboItem.DisplayMember = "item desc"

            ItemLoading = False

        Catch ex As Exception

            MessageBox.Show("Error:" & ex.Message, "Error", MessageBoxButtons.OK, MessageBoxIcon.Error)

        End Try

    End Sub

Those procedures are called from the SelectIndexChanged events of cboTemplate and cboCustomer, respectfully.

I find that in my testing, these SelectIndexChanged events are fired numerous times - every time I add a DataSource, every time I add a DisplayMember.

I need to code this logic in such a way that the GUI does not hang for 5 seconds each time a user makes a change. What can I use other than SelectIndexChanged?

(One way I tried to get around this is the boolean CustomerLoading and ItemLoading. I change them to True when the datasource and displaymember are being loaded and false otherwise, and try to skip the myriad times the procedures are fired by testing for a False value in the SelectIndexChanged, but either I'm not doing it right, or I'm missing something.)

Please assist!