Created a UserControl in wpf with calendar & TextBox and need to Assign value for UserControl's TextBox, from a hosted wpf window and for dynamically added UserControl as well?

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WPF

This is the code

CdrControl.UserControl1 txtAttribute5 = new CdrControl.UserControl1();
txtAttribute5.Width = 100;
txtAttribute5.Height = Double.NaN;
txtAttribute5.IsEnabled = true;
txtAttribute5.Name = "CdrCalendar" + GenerateCode();

txtAttribute5.Margin = new Thickness(0, 0, 0, 15);
txtAttribute5.GotFocus += new RoutedEventHandler(txtAttribute5_GotFocus);
txtAttribute5.LostFocus += new RoutedEventHandler(txtAttribute5_LostFocus);
stackpanel.Children.Add(txtAttribute5);
(txtAttribute5.FindName("txtDate") as TextBox).Text = text;//Assigned a Value here

This is not working....