public class ListBoxHelper
{
#region SelectedItems
///
/// SelectedItems Attached Dependency Property
///
public static readonly DependencyProperty SelectedItemsProperty =
DependencyProperty.RegisterAttached("SelectedItems", typeof (IList),
typeof (ListBoxHelper),
new FrameworkPropertyMetadata((IList) null,
new PropertyChangedCallback(OnSelectedItemsChanged)));
/// <summary>
/// Gets the SelectedItems property.
/// </summary>
/// <param name="d"></param>
/// <returns></returns>
public static IList GetSelectedItems(DependencyObject d)
{
return (IList) d.GetValue(SelectedItemsProperty);
}
/// <summary>
/// Sets the SelectedItems property.
/// </summary>
/// <param name="d"></param>
/// <param name="value"></param>
public static void SetSelectedItems(DependencyObject d, IList value)
{
d.SetValue(SelectedItemsProperty, value);
}
/// <summary>
/// Called when SelectedItems is set
/// </summary>
/// <param name="d"></param>
/// <param name="e"></param>
private static void OnSelectedItemsChanged(DependencyObject d,
DependencyPropertyChangedEventArgs e)
{
var listBox = (ListBox) d;
SetInternalSelectedItemsToPublic(listBox);
IList selectedItems = GetSelectedItems(listBox);
if (selectedItems is ObservableCollection<object>)
{
// if the list is a observable collection binde to the changed event
// to update the internal collection
(selectedItems as ObservableCollection<object>).CollectionChanged += delegate
{
SetSelectedDataItemsToInternal(listBox);
};
}
listBox.SelectionChanged += delegate
{
SetInternalSelectedItemsToPublic(listBox);
};
}
#region Implementation
static bool _isChanging;
private static void SetSelectedDataItemsToInternal(ListBox listBox)
{
if (_isChanging)
return;
_isChanging = true;
var selectedDataItems = GetSelectedItems(listBox);
if (listBox.SelectedItems != null)
{
listBox.SelectedItems.Clear();
if (selectedDataItems == null)
{
_isChanging = false;
return;
}
foreach (var item in selectedDataItems)
listBox.SelectedItems.Add(item);
}
_isChanging = false;
}
private static void SetInternalSelectedItemsToPublic(ListBox listBox)
{
if (_isChanging)
return;
_isChanging = true;
var selectedDataItems = GetSelectedItems(listBox);
if (selectedDataItems == null)
{
// the bound data type is not of typ IList / IList<object> /
// IEnumerable / Ienumerable<object>
// in this case the bound property has to be initialized first by the caller
_isChanging = false;
return;
}
selectedDataItems.Clear();
if (listBox.SelectedItems != null)
{
foreach (var item in listBox.SelectedItems)
selectedDataItems.Add(item);
}
_isChanging = false;
}
#endregion
#endregion
}
And here is the XAML with the binding:
<ListBox ItemsSource="{Binding ListItems}"
c:ListBoxHelper.SelectedItems="{Binding SlectedListItems}"
SelectionMode="Multiple"/>
