changed to use OnListItemsChanged event

Sample Applications/ExpenseIt/ExpenseItDemo/CreateExpenseReportDialogBox.cs

@@ -19,10 +19,6 @@ public partial class CreateExpenseReportDialogBox : Window
         public CreateExpenseReportDialogBox()
         {
             InitializeComponent();
-
-            var app = Application.Current;
-            var expenseReport = (ExpenseReport) app.FindResource("ExpenseData");
-            expenseReport?.EnsureInitialized();
         }
 
         private void addExpenseButton_Click(object sender, RoutedEventArgs e)

Sample Applications/ExpenseIt/ExpenseItDemo/ExpenseReport.cs

@@ -17,27 +17,13 @@ public class ExpenseReport : INotifyPropertyChanged
         private string _costCenter;
         private string _employeeNumber;
         private int _totalExpenses;
-        private bool _initialized = false;
 
         public ExpenseReport()
         {
             LineItems = new LineItemCollection();
             LineItems.LineItemCostChanged += OnLineItemCostChanged;
         }
 
-        /*
-         * This method is needed because this app operates on a singleton ExpenseReport.
-         * It preloads that report with real LineItems directly from the markup. 
-         * Doing that, the markup call IList.Add avoiding the override created on the class.
-         * So, we need to ensure the List class subscribes to the Item's events after its creation.
-         * */
-        public void EnsureInitialized()
-        {
-            if (_initialized) return;
-            _initialized = true;
-            LineItems.InitializeItems();
-        }
-
         public string Alias
         {
             get { return _alias; }

Sample Applications/ExpenseIt/ExpenseItDemo/LineItemCollection.cs

@@ -2,7 +2,9 @@
 // // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
 using System;
+using System.Collections.Generic;
 using System.Collections.ObjectModel;
+using System.Collections.Specialized;
 using System.ComponentModel;
 
 namespace ExpenseItDemo
@@ -11,28 +13,28 @@ public class LineItemCollection : ObservableCollection<LineItem>
     {
         public event EventHandler LineItemCostChanged;
 
-        public void InitializeItems()
+        public LineItemCollection()
         {
-            for(int i = 0; i < Items.Count; i++)
-            {
-                Items[i].PropertyChanged += LineItemPropertyChanged;
-            }
+            CollectionChanged += OnListItemsChanged;
         }
 
-        public new void Add(LineItem item)
+        private void LineItemPropertyChanged(object sender, PropertyChangedEventArgs e)
         {
-            if (item != null)
+            if (e.PropertyName == "Cost")
             {
-                item.PropertyChanged += LineItemPropertyChanged;
+                OnLineItemCostChanged(this, new EventArgs());
             }
-            base.Add(item);
         }
 
-        private void LineItemPropertyChanged(object sender, PropertyChangedEventArgs e)
+        private void OnListItemsChanged(object sender, NotifyCollectionChangedEventArgs e)
         {
-            if (e.PropertyName == "Cost")
+            if(e.Action == NotifyCollectionChangedAction.Add)
             {
-                OnLineItemCostChanged(this, new EventArgs());
+                for(int i = 0; i < e.NewItems.Count; i++)
+                {
+                    LineItem item = e.NewItems[i] as LineItem;
+                    item.PropertyChanged += LineItemPropertyChanged;
+                }
             }
         }