MVVM # Episode 3

using System;
using System.Windows.Input;
using System.Windows.Threading;
using Messengers;


namespace ViewModels
{
    /// <summary>
    /// This view model expects the user to be able to select from a list of 
    /// Customers, sending a message when one is selected.
    /// On selection, the Controller will be asked to show the details of the selected Customer
    /// </summary>
    public class CustomerSelectionViewModel : BaseViewModel
    {
        #region Private Fields
        DispatcherTimer stateFilterTimer;
        #endregion
        #region Properties

        /// <summary>
        /// Just to save us casting the base class's IController to ICustomerController all the time...
        /// </summary>
        private ICustomerController CustomerController
        {
            get
            {
                return (ICustomerController)Controller;
            }
        }

        #region Observable Properties

        private CustomerListItemViewData selectedItem;
        public CustomerListItemViewData SelectedItem
        {
            get
            {
                return selectedItem;
            }
            set
            {
                if (value != selectedItem)
                {
                    selectedItem = value;
                    RaisePropertyChanged("SelectedItem");
                }
            }
        }
        private string stateFilter;
        public string StateFilter
        {
            get
            {
                return stateFilter;
            }
            set
            {
                if (value != stateFilter)
                {
                    stateFilterTimer.Stop();
                    stateFilter = value;
                    RaisePropertyChanged("StateFilter");
                    stateFilterTimer.Start();
                }
            }
        }
        #endregion
        #endregion

        #region Commands
        #region Command Relays
        private RelayCommand userSelectedItemCommand;
        public ICommand UserSelectedItemCommand
        {
            get
            {
                return userSelectedItemCommand ?? (userSelectedItemCommand = new RelayCommand(() => ObeyUserSelectedItemCommand()));
            }
        }
        #endregion
        #region Command Handlers
        private void ObeyUserSelectedItemCommand()
        {
            CustomerController.CustomerSelectedForEdit(this.SelectedItem, this);
        }
        #endregion
        #endregion

        #region Constructors
        /// <summary>
        /// Required to allow our DesignTime version to be instantiated
        /// </summary>
        protected CustomerSelectionViewModel()
        {
        }

        public CustomerSelectionViewModel(ICustomerController controller, string stateFilter = "")
            : this(controller, null, stateFilter)
        {

        }

        /// <summary>
        /// Use the base class to store the controller and set the Data Context of the view (view)
        /// Initialise any data that needs initialising
        /// </summary>
        /// <param name="controller"></param>
        /// <param name="view"></param>
        public CustomerSelectionViewModel(ICustomerController controller, IView view, string stateFilter = "")
            : base(controller, view)
        {
            controller.Messenger.Register(MessageTypes.MSG_CUSTOMER_SAVED, new Action<Message>(RefreshList));
            // Leave it for half a second before filtering on State
            stateFilterTimer = new DispatcherTimer()
            {
                Interval = new TimeSpan(0, 0, 0, 0, 500)
            };
            stateFilterTimer.Tick += StateFilterTimerTick;
            StateFilter = stateFilter;
            RefreshList();
        }
        #endregion

        #region Private Methods
        /// <summary>
        /// Event handler for the timer used for 'filter as you type' on the State filter.
        /// When the timer triggers, filter the list with the existing filter.
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        void StateFilterTimerTick(object sender, EventArgs e)
        {
            stateFilterTimer.Stop();
            RefreshList();
        }

        private void RefreshList(Message message)
        {
            RefreshList();
            message.HandledStatus = MessageHandledStatus.HandledContinue;
        }

        /// <summary>
        /// Ask for an updated list of customers based on the filter
        /// </summary>
        private void RefreshList()
        {
            ViewData = CustomerController.GetCustomerSelectionViewData(StateFilter);
        }

        #endregion

    }
}