private void btnManageUsers_Click(object sender, System.Windows.RoutedEventArgs e)
        {
            if (_manageUsersWindow == null)
            {
                _manageUsersWindow = new ManageUsersWindow();
                _manageUsersWindow.Closed += Window_Closed;
            }

            _manageUsersWindow.Show();
            _manageUsersWindow.WindowState = WindowState.Normal;
        }
        void Window_Closed(object sender, EventArgs e)
        {
            if (sender is AgendaWindow)
            {
                _agendaWindow = null;
            }
            else if (sender is ManageUsersWindow)
            {
                _manageUsersWindow = null;
            }
            else if (sender is ManageRemindersWindow)
            {
                _manageRemindersWindow = null;
                RefreshRemindersStackPanel();
            }
            else if (sender is ManageMedicinesWindow)
            {
                _manageMedicinesWindow = null;
                RefreshMedicinesStackPanel();
            }
            else if (sender is ManageTreatmentsWindow)
            {
                _manageTreatmentsWindow = null;
            }
            else if (sender is ManageReceivedInvoicesWindow)
            {
                _manageReceivedInvoicesWindow = null;
            }
            else if (sender is ManageOutgoingInvoicesWindow)
            {
                _manageOutgoingInvoicesWindow = null;
            }
            else if (sender is TotalInvoicesWindow)
            {
                _totalInvoicesWindow = null;
            }
            else if (sender is ManageProvidersWindow)
            {
                _manageProvidersWindow = null;
            }
            else if (sender is ManageTechnicalsWindow)
            {
                _manageTechnicalsWindow = null;
            }
            else if (sender is ManageLaboratoryWorksWindow)
            {
                _manageLaboratoryWorksWindow = null;
            }
            else if (sender is MedicalProofDocument)
            {
                _medicalProofDocumentWindow = null;
            }
            else if (sender is ManageGeneralPaidsWindow)
            {
                _manageGeneralPaidsWindow = null;
            }
            else if (sender is ManageContactsWindow)
            {
                _manageContactsWindow = null;
            }
            else if (sender is ManageCleanedMaterialsWindow)
            {
                _manageCleanedMaterialsWindow = null;
            }
            else if (sender is SendEmailWindow)
            {
                _sendEmailWindow = null;
            }
            else if (sender is ConfigureEmailWindow)
            {
                _configureEmailWindow = null;
            }
            else if (sender is ManagePatientsWindow)
            {
                _managePatientsWindow = null;
            }
            else if (sender is ManageDotationsWindow)
            {
                _manageDotationsWindow = null;
                RefreshDotationsStackPanel();
            }
            else if (sender is ManageTreatmentPricesWindow)
            {
                _manageTreatmentPricesWindow = null;
            }
            else if (sender is ManageBudgetsWindow)
            {
                _manageBudgetsWindow = null;
            }
            else if (sender is ManageAmericanExpressPaidsWindow)
            {
                _manageAmericanExpressPaidsWindow = null;
            }
            else if (sender is ManageAuthorizationsWindow)
            {
                _manageAuthorizationsWindow = null;
            }
            else if (sender is ManageDentegraAuthorizationsWindow)
            {
                _manageElegibilitiesWindow = null;
            }
            else if (sender is ManageDrawersWindow)
            {
                _manageDrawersWindow = null;
            }
            else if (sender is CashRegisterWindow)
            {
                _cashRegisterWindow = null;
            }
            else if (sender is ManageBanksWindow)
            {
                _manageBanksWindow = null;
            }
            else if (sender is ViewPaymentsWindow)
            {
                _viewPaymentsWindow = null;
            }
            else if (sender is ViewPaymentFoliosWindow)
            {
                _viewPaymentFoliosWindow = null;
            }
            else if (sender is ViewEventsWindow)
            {
                _viewEventsWindow = null;
            }
            else if (sender is ViewPendingPaymentsWindow)
            {
                _viewPendingPaymentsWindow = null;
            }
            else if (sender is FinishedEventsReminderModal)
            {
                _finishedEventsReminderModal = null;

                List<DateTime> datesUpdated = (sender as FinishedEventsReminderModal).FinishedEvents
                                                .Where(fe => fe.IsCompleted || fe.IsCanceled)
                                                .Select(fe => (new DateTime(fe.StartEvent.Year, fe.StartEvent.Month, fe.StartEvent.Day)))
                                                .Distinct()
                                                .ToList();

                if (datesUpdated.Count > 0 && _agendaWindow != null)
                {
                    _agendaWindow.RepaintSchedulerIfDateModifiedIsSelected(datesUpdated);
                }
            }
        }