Building WPF Applications with Self-Tracking Entity Generator - Project Setup

using System.ComponentModel;
using System.Windows;
using System.Windows.Controls;

namespace SchoolSample
{
    public class ComboBoxEx : ComboBox
    {
        #region Fields
        private bool _suppressSelectionChangedUpdatesRebind;
        #endregion

        #region Properties

        public static readonly DependencyProperty SelectedValueProperProperty =
            DependencyProperty.Register(
                "SelectedValueProper",
                typeof(object),
                typeof(ComboBoxEx),
                new PropertyMetadata((o, dp) =>
                {
                    var comboBoxEx = o as ComboBoxEx;
                    if (comboBoxEx == null)
                        return;

                    comboBoxEx.SetSelectedValueSuppressingChangeEventProcessing(dp.NewValue);
                }));

        [Browsable(true), EditorBrowsable(EditorBrowsableState.Always)]
        public object SelectedValueProper
        {
            get { return GetValue(SelectedValueProperProperty); }
            set { SetValue(SelectedValueProperProperty, value); }
        }

        #endregion

        #region Constructor and Overrides

        public ComboBoxEx()
        {
            SelectionChanged += ComboBoxEx_SelectionChanged;
        }

        /// <summary>
        /// Updates the current selected item when the <see cref="P:System.Windows.Controls.ItemsControl.Items"/> collection has changed.
        /// </summary>
        /// <param name="e">Contains data about changes in the items collection.</param>
        protected override void OnItemsChanged(System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
        {
            // Must re-apply value here because the combobox has a bug that 
            // despite the fact that the binding still exists, it doesn't 
            // re-evaluate and subsequently drops the binding on the change event
            SetSelectedValueSuppressingChangeEventProcessing(SelectedValueProper);
        }

        #endregion

        #region Events

        private void ComboBoxEx_SelectionChanged(object sender, SelectionChangedEventArgs e)
        {
            // Avoid recursive stack overflow
            if (_suppressSelectionChangedUpdatesRebind)
                return;

            if (e.AddedItems != null && e.AddedItems.Count > 0)
            {
                SelectedValueProper = SelectedValue;
            }
            // Do not apply the value if no items are selected (ie. the else)
            // because that just passes on the null-value bug from the combobox
        }

        #endregion

        #region Helpers

        /// <summary>
        /// Sets the selected value suppressing change event processing.
        /// </summary>
        /// <param name="newSelectedValue">The new selected value.</param>
        private void SetSelectedValueSuppressingChangeEventProcessing(object newSelectedValue)
        {
            try
            {
                _suppressSelectionChangedUpdatesRebind = true;
                SelectedValue = newSelectedValue;
            }
            finally
            {
                _suppressSelectionChangedUpdatesRebind = false;
            }
        }

        #endregion
    }
}