Event ของ Combobox ครับ.... ผมใช้ VS-2005 + Window Apps....

    Private Sub Customers_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        If F_Connection(conn) = False Then Exit Sub
        Call_province()
        call_amphur()
    End Sub
    Private Sub Call_province()
        If F_Connection(conn) = False Then Exit Sub
        ds.Tables.Clear()
        Try
            ls_sql = "SELECT provinceid,des FROM tblprovince "
            ls_sql &= "ORDER BY des"
            da = New SqlDataAdapter(ls_sql, conn)
            da.Fill(ds, "province")
            If ds.Tables("province").Rows.Count <> 0 Then
                With cb_province
                    .DataSource = ds.Tables("province")
                    .DisplayMember = "des"
                    .ValueMember = "provinceid"
                End With
            End If
        Catch ex As Exception
            MessageBox.Show(ex.Message, "", MessageBoxButtons.OK, MessageBoxIcon.Error)
        End Try

    End Sub

    Private Sub call_amphur()
        ds.Tables.Clear()
        Try
            ls_sql = "SELECT amphur_id,des FROM tblamphur "
            If cb_province.ValueMember = "" Then
                Exit Sub
            Else
                ls_sql &= "where province_id = '" & CStr(cb_province.SelectedValue) & "'"

                ls_sql &= "ORDER BY des"
                da = New SqlDataAdapter(ls_sql, conn)
                da.Fill(ds, "tblamphur")
                If ds.Tables("tblamphur").Rows.Count <> 0 Then
                    With cb_amphur
                        .DataSource = ds.Tables("tblamphur")
                        .DisplayMember = "des"
                        .ValueMember = "amphur_id"
                    End With
                End If
            End If
        Catch ex As Exception
            MessageBox.Show(ex.Message, "", MessageBoxButtons.OK, MessageBoxIcon.Error)
        End Try
    End Sub

    Private Sub cb_province_SelectedValueChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cb_province.SelectedValueChanged
        call_amphur()
    End Sub