Overcome missing TabControl SelectionChanging event with wpf in a MVVM manner

• Purpose: we want to be able to intervent before leaving a TabItem and for example to cancel before the new TabItem has been selected, if necessary.
• Problem: the wpf TabControl doesn't know SelectionChanging respectively PreviewSelectionChanged event (by the way Teleriks RadTabControl knows it).
• Prerequisites: wpf and catel framework.
• Solution:

<catel:datawindow ...loaded="DataWindow_Loaded">
...
	<tabcontrol x:name="TabCtrlMain" issynchronizedwithcurrentitem="True">
	<tabitem regions:regionmanager.regionname="{x: Static utils:RegionNames.MainContentRegion}">
	<tabitem regions:regionmanager.regionname="{x: Static utils:RegionNames.AuswertungRegion}">         	

#region Properties
...
/// 

/// We want the ViewModel know the TabItems collection of the TabControl so it can observe the navigation between the
/// TabItems in a manner where it is e.g. possible to prevent the navigation if a ViewModel is dirty.
/// 
/// 
/// credits:
/// http://joshsmithonwpf.wordpress.com/2009/09/04/how-to-prevent-a-tabitem-from-being-selected/
/// http://marlongrech.wordpress.com/2008/11/22/icollectionview-explained/
/// 
[ViewToViewModel]
public ICollectionView TabItemsCollection
{
	get { return ( ICollectionView)GetValue(TabItemsCollectionProperty); }
	set { SetValue(TabItemsCollectionProperty, value); }
}
// Using a DependencyProperty as the backing store for TabItemsCollection. This enables animation, styling, binding, etc...
public static readonly DependencyProperty TabItemsCollectionProperty =
    DependencyProperty.Register("TabItemsCollection" , typeof (ICollectionView ), typeof(ShellView ), new UIPropertyMetadata (null ));
#endregion
#region Methods
...
/// 

/// This method is called after the ViewModel is initialized. So we can initialize here the TabItemsCollection,
/// since we are not able to populate it when registering.
/// 
/// 
/// 
private void DataWindow_Loaded( object sender, RoutedEventArgs e)
{
if (TabItemsCollection == null)
	TabItemsCollection = CollectionViewSource.GetDefaultView(TabCtrlMain.Items);
}
#endregion

#region Constructor
public ShellViewModel()
{
	...
	TabItemsCollection.CurrentChanging += OnTabItemsCollectionCurrentChanging;
	...
}
#endregion
#region Properties
...
/// 

/// Gets or sets the TabItemsCollection property value which is populated from View.
/// 
public ICollectionView TabItemsCollection { get ; set ; }
#endregion
#region Methods
...
/// 

/// Observe the navigation between the TabItems, save BEFORE leaving the current TabItem.
/// For this to run the TabControl within the View needs to set IsSynchronizedWithCurrentItem="True".
/// 
/// 
/// 
private void OnTabItemsCollectionCurrentChanging(object sender, CurrentChangingEventArgs e)
{
	var collection = sender as ItemCollection;
	if (collection != null)
	{
	var itemCollection = collection;
	var currentTabItem = (TabItem)itemCollection.CurrentItem;
	...
	}
}
...
/// 

/// Unsubscribe.
/// 
protected override void Close()
{
	TabItemsCollection.CurrentChanging -= OnTabItemsCollectionCurrentChanging;
}