Silverlight windows phone 7

See more:

.NET

Hi,

This application is related to sending group sms and at present Im saving it in the database. When I select the item in the combo box I will get the contacts related to it. Im selecting the contacts using checkbox, I should be able to send sms to the contacts that I check. Just go through the below code

<ListBox Height="326" HorizontalAlignment="Left"
                    Margin="6,101,0,0" Visibility="Visible"
                    Name="lbContacts" VerticalAlignment="Top" Width="300" ItemsSource="{Binding}" >
               <ListBox.ItemTemplate>
                   <DataTemplate>
                       <ListBoxItem>
                           <StackPanel Orientation="Vertical">
                               <CheckBox Name="chkContactName" Content="{Binding ContactName}" />
                               <TextBlock Name="tbMobileNo" Text="{Binding MobileNo}"/>

                           </StackPanel>
                       </ListBoxItem>
                   </DataTemplate>
               </ListBox.ItemTemplate>
           </ListBox>
           <TextBox Height="132" HorizontalAlignment="Left" Margin="-13,433,0,0" Name="txtMessage" VerticalAlignment="Top" Width="460" />
           <Button Content="Send" Height="72" HorizontalAlignment="Left" Margin="287,566,0,0" Name="btnSend" VerticalAlignment="Top" Width="160" Click="btnSend_Click" />

and the below code is to iterate through all the items in the listbox.
//Im getting the exception as invalid cast exception in the below foreach loop

private void btnSend_Click(object sender, RoutedEventArgs e)
       {
           List<string> lst = new List<string>();

           foreach(ListBoxItem li in lbContacts.Items)
           {
               CheckBox chk = (CheckBox)li.FindName("chkContactName");
               if (chk.IsChecked==true)
               {
                   TextBlock tbmob = (TextBlock)li.FindName("tbMobileNo");
                   lst.Add(tbmob.Text);
               }
           }
           for (int i = 0; i < lst.Count; i++)
           {
               SM objsms = new SM();
               objsms.FKUserId = fkuserid;
               objsms.FKContactId = ((Contact)lbContacts.SelectedItem).PKContactId;
               objsms.Message = txtMessage.Text;
               objsms.SentDate = System.DateTime.Now;
               try
               {
                   proxy.InsertSMSAsync(objsms);
                   MessageBox.Show("SMS sent successfully");
               }
               catch
               {
                   MessageBox.Show("SMS cannot be sent");
               }
           }
       }

can anyone help me to solve this problem