Dan Soltesz -blog .NET geek in disguise

Sometimes your list boxes can have a lot of items in them.  Even though you may order the list it still can be difficult for the user to find and item.  I like to give the user the abiltiy to search for an item in the listbox.  To keep this clean with MVVM, I created a behavior that can autoscroll for your via databinding.

Here is the behavior

/// <summary>
    /// Auto scroll listbox to item that is bound to the FoundItem property
    /// </summary>
    public class ListBoxItemAutoScrollBehavior : Behavior<ListBox>
    {
        #region Properties
        /// <summary>
        /// Item that is bound to listbox that you want to autoscroll to
        /// </summary>
        public object FoundItem
        {
            get { return GetValue(FoundItemProperty); }
            set { SetValue(FoundItemProperty, value); }
        }
 
        public static readonly DependencyProperty FoundItemProperty = DependencyProperty.Register("FoundItem", typeof(object), typeof(ListBoxItemAutoScrollBehavior), new PropertyMetadata(FoundItemChanged));
 
        private static void FoundItemChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            ((ListBoxItemAutoScrollBehavior)d).AssociatedObject.ScrollIntoView(e.NewValue);
        }
        #endregion
    }

Make sure you add a reference to System.Windows.Interactivity.

To use the behavior I do something like this.

<ListBox ItemsSource="{Binding MyItems}"  DisplayMemberPath="ItemName"  SelectionMode="Multiple">
                        <i:Interaction.Behaviors>
                            <behaviors:ListBoxItemAutoScrollBehavior FoundItem="{Binding FoundItem}"/>
                        </i:Interaction.Behaviors>
                    </ListBox>

<TextBox Text="{Binding ItemToFind, Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}" BorderThickness="1" />

Now in your view model just define your properties to bind to.

public ObservableCollection<Item> MyItems
        {
            get { return _myItems; }
            set
            {
 
                if (_myItems == value) return;
                _myItems = value;
                OnPropertyChanged(() => MyItems);
            }
        }
 
        public string ItemToFind
        {
            get { return _itemToFind; }
            set
            {
                if (_itemToFind == value) return;
                _itemToFind = value;
                 FoundItem = MyItems.FirstOrDefault(o => o.ItemName.StartsWith(_itemToFind, StringComparison.CurrentCultureIgnoreCase));
                OnPropertyChanged(() => ItemToFind);
                OnPropertyChanged(() => FoundItem);
            }
        }
         public Item FoundItem { get; set; }

 Now when the user types in something into the textbox, it will autoscroll to the item that is found