Hello,

these are my 2 classes a Attachable Property SelectedItems:

code is from here: http://stackoverflow.com/questions/1297643/sync-selecteditems-in-a-muliselect-listbox-with-a-collection-in-viewmodel

The namespace TBM.Helper is for sure proper as it works for other classes too.

The namespace reference is also in the xaml file:

xmlns:Helper="clr_namespace:TBM.Helper"

But <ListBox Helper:SelectedItems.Items="{Binding SelectedItems}" ...

does not work because =>

The property 'SelectedItems.Items' does not exist in XML namespace 'clr_namespace:TBM.Helper'. The attachable property 'Items' was not found in type 'SelectedItems

What do I have to change ?

    using System;

using System.Collections.Generic; using System.Linq; using System.Text; using System.Windows.Controls; using System.Collections; using System.Windows;

namespace TBM.Helper { public static class SelectedItems : DependencyObject { private static readonly DependencyProperty SelectedItemsBehaviorProperty = DependencyProperty.RegisterAttached( "SelectedItemsBehavior", typeof(SelectedItemsBehavior), typeof(ListBox), null);

    public static readonly DependencyProperty ItemsProperty = DependencyProperty.RegisterAttached(
            "Items",
            typeof(IList),
            typeof(SelectedItems),
            new PropertyMetadata(null, ItemsPropertyChanged));

    public static void SetItems(ListBox listBox, IList list) { listBox.SetValue(ItemsProperty, list); }
    public static IList GetItems(ListBox listBox) { return listBox.GetValue(ItemsProperty) as IList; }

    private static void ItemsPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        var target = d as ListBox;
        if (target != null)
        {
            GetOrCreateBehavior(target, e.NewValue as IList);
        }
    }

    private static SelectedItemsBehavior GetOrCreateBehavior(ListBox target, IList list)
    {
        var behavior = target.GetValue(SelectedItemsBehaviorProperty) as SelectedItemsBehavior;
        if (behavior == null)
        {
            behavior = new SelectedItemsBehavior(target, list);
            target.SetValue(SelectedItemsBehaviorProperty, behavior);
        }

        return behavior;
    }
}

}

using System.Windows;

using System.Windows.Controls; using System.Collections;

namespace TBM.Helper { public class SelectedItemsBehavior { private readonly ListBox _listBox; private readonly IList _boundList;

    public SelectedItemsBehavior(ListBox listBox, IList boundList)
    {
        _boundList = boundList;
        _listBox = listBox;

        SetSelectedItems();

        _listBox.SelectionChanged += OnSelectionChanged;
        _listBox.DataContextChanged += OnDataContextChanged;
    }

    private void SetSelectedItems()
    {
        _listBox.SelectedItems.Clear();

        foreach (object item in _boundList)
        {
            // References in _boundList might not be the same as in _listBox.Items
            int i = _listBox.Items.IndexOf(item);
            if (i >= 0)
                _listBox.SelectedItems.Add(_listBox.Items[i]);
        }
    }

    private void OnDataContextChanged(object sender, DependencyPropertyChangedEventArgs e)
    {
        SetSelectedItems();
    }

    private void OnSelectionChanged(object sender, SelectionChangedEventArgs e)
    {
        _boundList.Clear();

        foreach (var item in _listBox.SelectedItems)          
            _boundList.Add(item);           
    }
}

}