/// <summary>
/// ItemsSourceChanged Behavior uses an Attached Dependency Property
/// to add and raise a rotued event whenever an ItemsControl's ItemsSource property
/// changes. Also looks for INotifyCollectionChanged on the ItemsSource and raises the
/// event on every collection changed event
/// </summary>
public static class ItemsSourceChangedBehavior
{
/// <summary>
/// ItemsSourceChanged Attached Dependency Property with Callback method
/// </summary>
public static readonly DependencyProperty ItemsSourceChangedProperty =
DependencyProperty.RegisterAttached("ItemsSourceChanged",
typeof(bool), typeof(ItemsSourceChangedBehavior),
new FrameworkPropertyMetadata(false, OnItemsSourceChanged));
/// <summary>
/// Static Get method allowing easy Xaml usage and to simplify the
/// GetValue process
/// </summary>
/// <param name="obj">The dependency obj.</param>
/// <returns>True or False</returns>
public static bool GetItemsSourceChanged(DependencyObject obj)
{
return (bool)obj.GetValue(ItemsSourceChangedProperty);
}
/// <summary>
/// Static Set method allowing easy Xaml usage and to simplify the
/// Setvalue process
/// </summary>
/// <param name="obj">The obj.</param>
/// <param name="value">if set to <c>true</c> [value].</param>
public static void SetItemsSourceChanged(DependencyObject obj, bool value)
{
obj.SetValue(ItemsSourceChangedProperty, value);
}
/// <summary>
/// Dependency Property Changed Call Back method. This will be called anytime
/// the ItemsSourceChangedProperty value changes on a Dependency Object
/// </summary>
/// <param name="obj">The obj.</param>
/// <param name="e">The <see cref="System.Windows.DependencyPropertyChangedEventArgs"/> instance containing the event data.</param>
private static void OnItemsSourceChanged(DependencyObject obj, DependencyPropertyChangedEventArgs e)
{
ItemsControl itemsControl = obj as ItemsControl;
if (itemsControl == null)
return;
bool oldValue = (bool)e.OldValue;
bool newValue = (bool)e.NewValue;
if (!oldValue && newValue) // If changed from false to true
{
// Create a binding to the ItemsSourceProperty on the ItemsControl
Binding b = new Binding
{
Source = itemsControl,
Path = new PropertyPath(ItemsControl.ItemsSourceProperty)
};
// Since the ItemsSourceListenerProperty is now bound to the
// ItemsSourceProperty on the ItemsControl, whenever the
// ItemsSourceProperty changes the ItemsSourceListenerProperty
// callback method will execute
itemsControl.SetBinding(ItemsSourceListenerProperty, b);
}
else if (oldValue && !newValue) // If changed from true to false
{
// Clear Binding on the ItemsSourceListenerProperty
BindingOperations.ClearBinding(itemsControl, ItemsSourceListenerProperty);
}
}
#endregion
#region Items Source Listener Property
/// <summary>
/// The ItemsSourceListener Attached Dependency Property is a private property
/// the ItemsSourceChangedBehavior will use silently to bind to the ItemsControl
/// ItemsSourceProperty.
/// Once bound, the callback method will execute anytime the ItemsSource property changes
/// </summary>
private static readonly DependencyProperty ItemsSourceListenerProperty =
DependencyProperty.RegisterAttached("ItemsSourceListener",
typeof(object), typeof(ItemsSourceChangedBehavior),
new FrameworkPropertyMetadata(null, OnItemsSourceListenerChanged));
/// <summary>
/// Dependency Property Changed Call Back method. This will be called anytime
/// the ItemsSourceListenerProperty value changes on a Dependency Object
/// </summary>
/// <param name="obj">The obj.</param>
/// <param name="e">The <see cref="System.Windows.DependencyPropertyChangedEventArgs"/> instance containing the event data.</param>
private static void OnItemsSourceListenerChanged(DependencyObject obj, DependencyPropertyChangedEventArgs e)
{
ItemsControl itemsControl = obj as ItemsControl;
if (itemsControl == null)
return;
INotifyCollectionChanged collection = e.NewValue as INotifyCollectionChanged;
if (collection != null)
{
collection.CollectionChanged += delegate
{
itemsControl.RaiseEvent(new RoutedEventArgs(ItemsSourceChangedEvent));
};
}
if (GetItemsSourceChanged(itemsControl))
itemsControl.RaiseEvent(new RoutedEventArgs(ItemsSourceChangedEvent));
}
#endregion
#region Items Source Changed Event
/// <summary>
/// Routed Event to raise whenever the ItemsSource changes on an ItemsControl
/// </summary>
public static readonly RoutedEvent ItemsSourceChangedEvent =
EventManager.RegisterRoutedEvent("ItemsSourceChanged",
RoutingStrategy.Bubble,
typeof(RoutedEventHandler),
typeof(ItemsControl));
#endregion
}
