Customizing the TreeView to allow multi select

The built-in WPF TreeView control does not allow for multi selection, like a ListBox does. How can I customize the TreeView to allow for multi selection without rewriting it.

I have a variation on SoMoS implementation that uses an attached property declared on a derivation of the base TreeView control to track the selection state of the TreeViewItems. This keeps the selection tracking on the TreeViewItem element itself, and off of the model object being presented by the tree-view.

This is the new TreeView class derivation.

using System.Linq;
using System.Windows;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Shapes;
using System.Windows.Controls;
using System.Collections;
using System.Collections.Generic;

namespace MultiSelectTreeViewDemo
{
    public sealed class MultiSelectTreeView : TreeView
    {
        #region Fields

        // Used in shift selections
        private TreeViewItem _lastItemSelected;

        #endregion Fields
        #region Dependency Properties

        public static readonly DependencyProperty IsItemSelectedProperty =
            DependencyProperty.RegisterAttached("IsItemSelected", typeof(bool), typeof(MultiSelectTreeView));

        public static void SetIsItemSelected(UIElement element, bool value)
        {
            element.SetValue(IsItemSelectedProperty, value);
        }
        public static bool GetIsItemSelected(UIElement element)
        {
            return (bool)element.GetValue(IsItemSelectedProperty);
        }

        #endregion Dependency Properties
        #region Properties

        private static bool IsCtrlPressed
        {
            get { return Keyboard.IsKeyDown(Key.LeftCtrl) || Keyboard.IsKeyDown(Key.RightCtrl); }
        }
        private static bool IsShiftPressed
        {
            get { return Keyboard.IsKeyDown(Key.LeftShift) || Keyboard.IsKeyDown(Key.RightShift); }
        }
    
        public IList SelectedItems
        {
            get
            {
                var selectedTreeViewItems = GetTreeViewItems(this, true).Where(GetIsItemSelected);
                var selectedModelItems = selectedTreeViewItems.Select(treeViewItem => treeViewItem.Header);

                return selectedModelItems.ToList();
            }
        }

        #endregion Properties
        #region Event Handlers

        protected override void OnPreviewMouseDown(MouseButtonEventArgs e)
        {
            base.OnPreviewMouseDown(e);

            // If clicking on a tree branch expander...
            if (e.OriginalSource is Shape || e.OriginalSource is Grid || e.OriginalSource is Border)
                return;

            var item = GetTreeViewItemClicked((FrameworkElement)e.OriginalSource);
            if (item != null) SelectedItemChangedInternal(item);
        }

        #endregion Event Handlers
        #region Utility Methods

        private void SelectedItemChangedInternal(TreeViewItem tvItem)
        {
            // Clear all previous selected item states if ctrl is NOT being held down
            if (!IsCtrlPressed)
            {
                var items = GetTreeViewItems(this, true);
                foreach (var treeViewItem in items)
                    SetIsItemSelected(treeViewItem, false);
            }

            // Is this an item range selection?
            if (IsShiftPressed && _lastItemSelected != null)
            {
                var items = GetTreeViewItemRange(_lastItemSelected, tvItem);
                if (items.Count > 0)
                {
                    foreach (var treeViewItem in items)
                        SetIsItemSelected(treeViewItem, true);

                    _lastItemSelected = items.Last();
                }
            }
            // Otherwise, individual selection
            else
            {
                SetIsItemSelected(tvItem, true);
                _lastItemSelected = tvItem;
            }
        }
        private static TreeViewItem GetTreeViewItemClicked(DependencyObject sender)
        {
            while (sender != null && !(sender is TreeViewItem))
                sender = VisualTreeHelper.GetParent(sender);
            return sender as TreeViewItem;
        }
        private static List<TreeViewItem> GetTreeViewItems(ItemsControl parentItem, bool includeCollapsedItems, List<TreeViewItem> itemList = null)
        {
            if (itemList == null)
                itemList = new List<TreeViewItem>();

            for (var index = 0; index < parentItem.Items.Count; index++)
            {
                var tvItem = parentItem.ItemContainerGenerator.ContainerFromIndex(index) as TreeViewItem;
                if (tvItem == null) continue;

                itemList.Add(tvItem);
                if (includeCollapsedItems || tvItem.IsExpanded)
                    GetTreeViewItems(tvItem, includeCollapsedItems, itemList);
            }
            return itemList;
        }
        private List<TreeViewItem> GetTreeViewItemRange(TreeViewItem start, TreeViewItem end)
        {
            var items = GetTreeViewItems(this, false);

            var startIndex = items.IndexOf(start);
            var endIndex = items.IndexOf(end);
            var rangeStart = startIndex > endIndex || startIndex == -1 ? endIndex : startIndex;
            var rangeCount = startIndex > endIndex ? startIndex - endIndex + 1 : endIndex - startIndex + 1;

            if (startIndex == -1 && endIndex == -1)
                rangeCount = 0;

            else if (startIndex == -1 || endIndex == -1)
                rangeCount = 1;

            return rangeCount > 0 ? items.GetRange(rangeStart, rangeCount) : new List<TreeViewItem>();
        }

        #endregion Utility Methods
    }
}

And here's the XAML. Make note that the salient part is the replacement of the two triggers that use the singular 'IsSelected' property with the new 'IsItemSelected' attached property in the MultiSelectTreeViewItemStyle to achieve the visual state.

Also note I'm not aggregating the new TreeView control into a UserControl.

<Window 
    x:Class="MultiSelectTreeViewDemo.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:MultiSelectTreeViewDemo"
    Title="MultiSelect TreeView Demo" Height="350" Width="525">

    <Window.Resources>
        <local:DemoViewModel x:Key="ViewModel"/>
        <Style x:Key="TreeViewItemFocusVisual">
            <Setter Property="Control.Template">
                <Setter.Value>
                    <ControlTemplate>
                        <Rectangle/>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>
        <SolidColorBrush x:Key="TreeViewItem.TreeArrow.Static.Checked.Fill" Color="#FF595959"/>
        <SolidColorBrush x:Key="TreeViewItem.TreeArrow.Static.Checked.Stroke" Color="#FF262626"/>
        <SolidColorBrush x:Key="TreeViewItem.TreeArrow.MouseOver.Stroke" Color="#FF1BBBFA"/>
        <SolidColorBrush x:Key="TreeViewItem.TreeArrow.MouseOver.Fill" Color="Transparent"/>
        <SolidColorBrush x:Key="TreeViewItem.TreeArrow.MouseOver.Checked.Stroke" Color="#FF262626"/>
        <SolidColorBrush x:Key="TreeViewItem.TreeArrow.MouseOver.Checked.Fill" Color="#FF595959"/>
        <PathGeometry x:Key="TreeArrow" Figures="M0,0 L0,6 L6,0 z"/>
        <SolidColorBrush x:Key="TreeViewItem.TreeArrow.Static.Fill" Color="Transparent"/>
        <SolidColorBrush x:Key="TreeViewItem.TreeArrow.Static.Stroke" Color="#FF989898"/>
        <Style x:Key="ExpandCollapseToggleStyle" TargetType="{x:Type ToggleButton}">
            <Setter Property="Focusable" Value="False"/>
            <Setter Property="Width" Value="16"/>
            <Setter Property="Height" Value="16"/>
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="{x:Type ToggleButton}">
                        <Border Background="Transparent" Height="16" Padding="5,5,5,5" Width="16">
                            <Path x:Name="ExpandPath" Data="{StaticResource TreeArrow}" Fill="{StaticResource TreeViewItem.TreeArrow.Static.Fill}" Stroke="{StaticResource TreeViewItem.TreeArrow.Static.Stroke}">
                                <Path.RenderTransform>
                                    <RotateTransform Angle="135" CenterY="3" CenterX="3"/>
                                </Path.RenderTransform>
                            </Path>
                        </Border>
                        <ControlTemplate.Triggers>
                            <Trigger Property="IsChecked" Value="True">
                                <Setter Property="RenderTransform" TargetName="ExpandPath">
                                    <Setter.Value>
                                        <RotateTransform Angle="180" CenterY="3" CenterX="3"/>
                                    </Setter.Value>
                                </Setter>
                                <Setter Property="Fill" TargetName="ExpandPath" Value="{StaticResource TreeViewItem.TreeArrow.Static.Checked.Fill}"/>
                                <Setter Property="Stroke" TargetName="ExpandPath" Value="{StaticResource TreeViewItem.TreeArrow.Static.Checked.Stroke}"/>
                            </Trigger>
                            <Trigger Property="IsMouseOver" Value="True">
                                <Setter Property="Stroke" TargetName="ExpandPath" Value="{StaticResource TreeViewItem.TreeArrow.MouseOver.Stroke}"/>
                                <Setter Property="Fill" TargetName="ExpandPath" Value="{StaticResource TreeViewItem.TreeArrow.MouseOver.Fill}"/>
                            </Trigger>
                            <MultiTrigger>
                                <MultiTrigger.Conditions>
                                    <Condition Property="IsMouseOver" Value="True"/>
                                    <Condition Property="IsChecked" Value="True"/>
                                </MultiTrigger.Conditions>
                                <Setter Property="Stroke" TargetName="ExpandPath" Value="{StaticResource TreeViewItem.TreeArrow.MouseOver.Checked.Stroke}"/>
                                <Setter Property="Fill" TargetName="ExpandPath" Value="{StaticResource TreeViewItem.TreeArrow.MouseOver.Checked.Fill}"/>
                            </MultiTrigger>
                        </ControlTemplate.Triggers>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>
        <Style x:Key="MultiSelectTreeViewItemStyle" TargetType="{x:Type TreeViewItem}">
            <Setter Property="Background" Value="Transparent"/>
            <Setter Property="HorizontalContentAlignment" Value="{Binding HorizontalContentAlignment, RelativeSource={RelativeSource AncestorType={x:Type ItemsControl}}}"/>
            <Setter Property="VerticalContentAlignment" Value="{Binding VerticalContentAlignment, RelativeSource={RelativeSource AncestorType={x:Type ItemsControl}}}"/>
            <Setter Property="Padding" Value="1,0,0,0"/>
            <Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.ControlTextBrushKey}}"/>
            <Setter Property="FocusVisualStyle" Value="{StaticResource TreeViewItemFocusVisual}"/>
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="{x:Type TreeViewItem}">
                        <Grid>
                            <Grid.ColumnDefinitions>
                                <ColumnDefinition MinWidth="19" Width="Auto"/>
                                <ColumnDefinition Width="Auto"/>
                                <ColumnDefinition Width="*"/>
                            </Grid.ColumnDefinitions>
                            <Grid.RowDefinitions>
                                <RowDefinition Height="Auto"/>
                                <RowDefinition/>
                            </Grid.RowDefinitions>
                            <ToggleButton 
                                x:Name="Expander" 
                                ClickMode="Press" 
                                IsChecked="{Binding IsExpanded, RelativeSource={RelativeSource TemplatedParent}}" 
                                Style="{StaticResource ExpandCollapseToggleStyle}"/>
                            <Border 
                                x:Name="Bd" 
                                BorderBrush="{TemplateBinding BorderBrush}" 
                                BorderThickness="{TemplateBinding BorderThickness}" 
                                Background="{TemplateBinding Background}" 
                                Grid.Column="1" 
                                Padding="{TemplateBinding Padding}" 
                                SnapsToDevicePixels="true">
                                <ContentPresenter 
                                    x:Name="PART_Header" 
                                    ContentSource="Header" 
                                    HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" 
                                    SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"/>
                            </Border>
                            <ItemsPresenter 
                                x:Name="ItemsHost" 
                                Grid.ColumnSpan="2" 
                                Grid.Column="1" 
                                Grid.Row="1"/>
                        </Grid>
                        <ControlTemplate.Triggers>
                            <Trigger Property="IsExpanded" Value="false">
                                <Setter Property="Visibility" TargetName="ItemsHost" Value="Collapsed"/>
                            </Trigger>
                            <Trigger Property="HasItems" Value="false">
                                <Setter Property="Visibility" TargetName="Expander" Value="Hidden"/>
                            </Trigger>
                            <!--Trigger Property="IsSelected" Value="true"-->
                            <Trigger Property="local:MultiSelectTreeView.IsItemSelected" Value="true">
                                <Setter Property="Background" TargetName="Bd" Value="{DynamicResource {x:Static SystemColors.HighlightBrushKey}}"/>
                                <Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.HighlightTextBrushKey}}"/>
                            </Trigger>
                            <MultiTrigger>
                                <MultiTrigger.Conditions>
                                    <!--Condition Property="IsSelected" Value="true"/-->
                                    <Condition Property="local:MultiSelectTreeView.IsItemSelected" Value="true"/>
                                    <Condition Property="IsSelectionActive" Value="false"/>
                                </MultiTrigger.Conditions>
                                <Setter Property="Background" TargetName="Bd" Value="{DynamicResource {x:Static SystemColors.InactiveSelectionHighlightBrushKey}}"/>
                                <Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.InactiveSelectionHighlightTextBrushKey}}"/>
                            </MultiTrigger>
                            <Trigger Property="IsEnabled" Value="false">
                                <Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.GrayTextBrushKey}}"/>
                            </Trigger>
                        </ControlTemplate.Triggers>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
            <Style.Triggers>
                <Trigger Property="VirtualizingPanel.IsVirtualizing" Value="true">
                    <Setter Property="ItemsPanel">
                        <Setter.Value>
                            <ItemsPanelTemplate>
                                <VirtualizingStackPanel/>
                            </ItemsPanelTemplate>
                        </Setter.Value>
                    </Setter>
                </Trigger>
            </Style.Triggers>
        </Style>
    </Window.Resources>

    <Grid
        Background="WhiteSmoke"
        DataContext="{DynamicResource ViewModel}">
        <Grid.RowDefinitions>
            <RowDefinition/>
            <RowDefinition Height="Auto"/>
        </Grid.RowDefinitions>
        <local:MultiSelectTreeView
            x:Name="multiSelectTreeView"
            ItemContainerStyle="{StaticResource MultiSelectTreeViewItemStyle}"
            ItemsSource="{Binding FoodGroups}">
            <local:MultiSelectTreeView.ItemTemplate>
                <HierarchicalDataTemplate ItemsSource="{Binding Children}">
                    <Grid>
                        <TextBlock FontSize="14" Text="{Binding Name}"/>
                    </Grid>
                </HierarchicalDataTemplate>
            </local:MultiSelectTreeView.ItemTemplate>
        </local:MultiSelectTreeView>
        <Button 
            Grid.Row="1" 
            Margin="0,10" 
            Padding="20,2"
            HorizontalAlignment="Center"
            Content="Get Selections" 
            Click="GetSelectionsButton_OnClick"/>
    </Grid>
</Window>

And here's a cheesy view-model to drive it (for demo purposes).

using System.Collections.ObjectModel;

namespace MultiSelectTreeViewDemo
{
    public sealed class DemoViewModel
    {
        public ObservableCollection<FoodItem> FoodGroups { get; set; }

        public DemoViewModel()
        {
            var redMeat = new FoodItem { Name = "Reds" };
            redMeat.Add(new FoodItem { Name = "Beef" });
            redMeat.Add(new FoodItem { Name = "Buffalo" });
            redMeat.Add(new FoodItem { Name = "Lamb" });
        
            var whiteMeat = new FoodItem { Name = "Whites" };
            whiteMeat.Add(new FoodItem { Name = "Chicken" });
            whiteMeat.Add(new FoodItem { Name = "Duck" });
            whiteMeat.Add(new FoodItem { Name = "Pork" });
            var meats = new FoodItem { Name = "Meats", Children = { redMeat, whiteMeat } };

            var veggies = new FoodItem { Name = "Vegetables" };
            veggies.Add(new FoodItem { Name = "Potato" });
            veggies.Add(new FoodItem { Name = "Corn" });
            veggies.Add(new FoodItem { Name = "Spinach" });

            var fruits = new FoodItem { Name = "Fruits" };
            fruits.Add(new FoodItem { Name = "Apple" });
            fruits.Add(new FoodItem { Name = "Orange" });
            fruits.Add(new FoodItem { Name = "Pear" });

            FoodGroups = new ObservableCollection<FoodItem> { meats, veggies, fruits };
        }
    }
    public sealed class FoodItem
    {
        public string Name { get; set; }
        public ObservableCollection<FoodItem> Children { get; set; }

        public FoodItem()
        {
            Children = new ObservableCollection<FoodItem>();
        }
        public void Add(FoodItem item)
        {
            Children.Add(item);
        }
    }
}

And here's the button click-handler on the MainWindow code-behind that shows the selections in a MessageBox.

    private void GetSelectionsButton_OnClick(object sender, RoutedEventArgs e)
    {
        var selectedMesg = "";
        var selectedItems = multiSelectTreeView.SelectedItems;

        if (selectedItems.Count > 0)
        {
            selectedMesg = selectedItems.Cast<FoodItem>()
                .Where(modelItem => modelItem != null)
                .Aggregate(selectedMesg, (current, modelItem) => current + modelItem.Name + Environment.NewLine);
        }
        else
            selectedMesg = "No selected items!";

        MessageBox.Show(selectedMesg, "MultiSelect TreeView Demo", MessageBoxButton.OK);
    }

Hope this helps.

When I consider overriding the fundamental behavior of a control, like a treeview, I always like to consider the usability and effort associated with my decision.

In the specific case of a treeview I find that switching to a listview in combination with zero, one, or more controls makes for a more usable solution that often is easier to implement.

As an example, consider the common Open dialog, or Windows Explorer application.

I've simplified this task adding a checkbox before the text for each treeviewitem.

So, I've created a dockpanel with 2 items inside: checkbox + textblock.

So...

XAML

<TreeView x:Name="treeViewProcesso" Margin="1,30.351,1,5"  BorderBrush="{x:Null}" MinHeight="250" VerticalContentAlignment="Top" BorderThickness="0" >
  <TreeViewItem Header="Documents" x:Name="treeView" IsExpanded="True" DisplayMemberPath="DocumentsId" >			
  </TreeViewItem>
</TreeView>

CS

TreeViewItem treeViewItem = new TreeViewItem();
DockPanel dp = new DockPanel();
CheckBox cb = new CheckBox();
TextBlock tb = new TextBlock();
tb.Text = "Item";
dp.Children.Add(cb);
dp.Children.Add(tb);
treeViewItem.Header = dp;
treeViewItem.Selected += new RoutedEventHandler(item_Selected);
treeView.Items.Add(treeViewItem);

And then you can access checkbox value:

void item_Selected(object sender, RoutedEventArgs e)
{
  selectedTVI = ((TreeViewItem)sender);

  CheckBox cb = (Checkbox)((DockPanel)selectedTVI.Header).Children[0];
}

This is a simple way to do if you don't need anything complex.

I finally ended coding my own CustomControl containing a TreeView inside. Based on the work of others the key of the functionality resides on making all the items of the Model of the TreeView inherit the interface ISelectable:

public interface ISelectable
{
    public bool IsSelected {get; set}
}

This way we will have a new 'IsSelected' property that has nothing to do with the TreeViewItem IsSelected. We just need to style our tree so it handles the model IsSelected property. Here the code (it's using the Drag & drop libraries available at http://code.google.com/p/gong-wpf-dragdrop/):

XAML

<UserControl x:Class="Picis.Wpf.Framework.ExtendedControls.TreeViewEx.TreeViewEx"
         
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:DragAndDrop="clr-namespace:Picis.Wpf.Framework.DragAndDrop">

<TreeView ItemsSource="{Binding ItemsSource, RelativeSource={RelativeSource AncestorType=UserControl}}" 
          ItemTemplate="{Binding ItemTemplate, RelativeSource={RelativeSource AncestorType=UserControl}}" 
          ItemContainerStyle="{Binding ItemContainerStyle, RelativeSource={RelativeSource AncestorType=UserControl}}" 
          DragAndDrop:DragDrop.DropHandler ="{Binding DropHandler, RelativeSource={RelativeSource AncestorType=UserControl}}" 
          PreviewMouseDown="TreeViewOnPreviewMouseDown" 
		  PreviewMouseUp="TreeViewOnPreviewMouseUp"
          x:FieldModifier="private" x:Name="InnerTreeView" >
    <TreeView.Resources>
        <Style TargetType="TreeViewItem">
            <Style.Resources>
                <SolidColorBrush x:Key="{x:Static SystemColors.HighlightBrushKey}" Color="White" />
                <SolidColorBrush x:Key="{x:Static SystemColors.HighlightTextBrushKey}" Color="Black" />
                <SolidColorBrush x:Key="{x:Static SystemColors.ControlBrushKey}" Color="White" />
            </Style.Resources>
        </Style>
    </TreeView.Resources>
</TreeView>

C#:

using System.Collections.Generic;
using System.Linq;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Shapes;
using GongSolutions.Wpf.DragDrop;
using DragDrop = GongSolutions.Wpf.DragDrop;

namespace <yournamespace>.TreeViewEx
{
public partial class TreeViewEx : UserControl
{
	#region Attributes

	private TreeViewItem _lastItemSelected; // Used in shift selections
	private TreeViewItem _itemToCheck; // Used when clicking on a selected item to check if we want to deselect it or to drag the current selection
	private bool _isDragEnabled;
	private bool _isDropEnabled;

	#endregion

	#region Dependency Properties

	public static readonly DependencyProperty ItemsSourceProperty = DependencyProperty.Register("ItemsSource", typeof(IEnumerable<ISelectable>), typeof(TreeViewEx));

	public IEnumerable<ISelectable> ItemsSource
	{
		get
		{
			return (IEnumerable<ISelectable>)this.GetValue(TreeViewEx.ItemsSourceProperty);
		}
		set
		{
			this.SetValue(TreeViewEx.ItemsSourceProperty, value);
		}
	}

	public static readonly DependencyProperty ItemTemplateProperty = DependencyProperty.Register("ItemTemplate", typeof(DataTemplate), typeof(TreeViewEx));

	public DataTemplate ItemTemplate
	{
		get
		{
			return (DataTemplate)GetValue(TreeViewEx.ItemTemplateProperty);
		}
		set
		{
			SetValue(TreeViewEx.ItemTemplateProperty, value);
		}
	}

	public static readonly DependencyProperty ItemContainerStyleProperty = DependencyProperty.Register("ItemContainerStyle", typeof(Style), typeof(TreeViewEx));

	public Style ItemContainerStyle
	{
		get
		{
			return (Style)GetValue(TreeViewEx.ItemContainerStyleProperty);
		}
		set
		{
			SetValue(TreeViewEx.ItemContainerStyleProperty, value);
		}
	}

	public static readonly DependencyProperty DropHandlerProperty = DependencyProperty.Register("DropHandler", typeof(IDropTarget), typeof(TreeViewEx));

	public IDropTarget DropHandler
	{
		get
		{
			return (IDropTarget)GetValue(TreeViewEx.DropHandlerProperty);
		}
		set
		{
			SetValue(TreeViewEx.DropHandlerProperty, value);
		}
	}

	#endregion

	#region Properties

	public bool IsDragEnabled
	{
		get
		{
			return _isDragEnabled;
		}
		set
		{
			if (_isDragEnabled != value)
			{
				_isDragEnabled = value;
				DragDrop.SetIsDragSource(this.InnerTreeView, _isDragEnabled);
			}
		}
	}

	public bool IsDropEnabled
	{
		get
		{
			return _isDropEnabled;
		}
		set
		{
			if (_isDropEnabled != value)
			{
				_isDropEnabled = value;
				DragDrop.SetIsDropTarget(this.InnerTreeView, _isDropEnabled);
			}
		}
	}

	#endregion

	#region Public Methods

	public TreeViewEx()
	{
		InitializeComponent();
	}

	#endregion

	#region Event Handlers

	private void TreeViewOnPreviewMouseDown(object sender, MouseButtonEventArgs e)
	{
		if (e.OriginalSource is Shape || e.OriginalSource is Grid || e.OriginalSource is Border) // If clicking on the + of the tree
			return;

		TreeViewItem item = this.GetTreeViewItemClicked((FrameworkElement)e.OriginalSource);

		if (item != null && item.Header != null)
		{
			this.SelectedItemChangedHandler(item);
		}
	}

	// Check done to avoid deselecting everything when clicking to drag
	private void TreeViewOnPreviewMouseUp(object sender, MouseButtonEventArgs e)
	{
		if (_itemToCheck != null)
		{
			TreeViewItem item = this.GetTreeViewItemClicked((FrameworkElement)e.OriginalSource);

			if (item != null && item.Header != null)
			{
				if (!TreeViewEx.IsCtrlPressed)
				{
					GetTreeViewItems(true).Select(t => t.Header).Cast<ISelectable>().ToList().ForEach(f => f.IsSelected = false);
					((ISelectable)_itemToCheck.Header).IsSelected = true;
					_lastItemSelected = _itemToCheck;
				}
				else
				{
					((ISelectable)_itemToCheck.Header).IsSelected = false;
					_lastItemSelected = null;
				}
			}
		}
	}

	#endregion

	#region Private Methods

	private void SelectedItemChangedHandler(TreeViewItem item)
	{
		ISelectable content = (ISelectable)item.Header;

		_itemToCheck = null;

		if (content.IsSelected)
		{
			// Check it at the mouse up event to avoid deselecting everything when clicking to drag
			_itemToCheck = item;
		}
		else
		{
			if (!TreeViewEx.IsCtrlPressed)
			{
				GetTreeViewItems(true).Select(t => t.Header).Cast<ISelectable>().ToList().ForEach(f => f.IsSelected = false);
			}

			if (TreeViewEx.IsShiftPressed && _lastItemSelected != null)
			{
				foreach (TreeViewItem tempItem in GetTreeViewItemsBetween(_lastItemSelected, item))
				{
					((ISelectable)tempItem.Header).IsSelected = true;
					_lastItemSelected = tempItem;
				}
			}
			else
			{
				content.IsSelected = true;
				_lastItemSelected = item;
			}
		}
	}

	private static bool IsCtrlPressed
	{
		get
		{
			return Keyboard.IsKeyDown(Key.LeftCtrl) || Keyboard.IsKeyDown(Key.RightCtrl);
		}
	}

	private static bool IsShiftPressed
	{
		get
		{
			return Keyboard.IsKeyDown(Key.LeftShift) || Keyboard.IsKeyDown(Key.RightShift);
		}
	}

	private TreeViewItem GetTreeViewItemClicked(UIElement sender)
	{
		Point point = sender.TranslatePoint(new Point(0, 0), this.InnerTreeView);
		DependencyObject visualItem = this.InnerTreeView.InputHitTest(point) as DependencyObject;
		while (visualItem != null && !(visualItem is TreeViewItem))
		{
			visualItem = VisualTreeHelper.GetParent(visualItem);
		}

		return visualItem as TreeViewItem;
	}

	private IEnumerable<TreeViewItem> GetTreeViewItemsBetween(TreeViewItem start, TreeViewItem end)
	{
		List<TreeViewItem> items = this.GetTreeViewItems(false);

		int startIndex = items.IndexOf(start);
		int endIndex = items.IndexOf(end);

		// It's possible that the start element has been removed after it was selected,
		// I don't find a way to happen on the end but I add the code to handle the situation just in case
		if (startIndex == -1 && endIndex == -1)
		{
			return new List<TreeViewItem>();
		}
		else if (startIndex == -1)
		{
			return new List<TreeViewItem>() {end};
		}
		else if (endIndex == -1)
		{
			return new List<TreeViewItem>() { start };
		}
		else
		{
			return startIndex > endIndex ? items.GetRange(endIndex, startIndex - endIndex + 1) : items.GetRange(startIndex, endIndex - startIndex + 1);	
		}
	}

	private List<TreeViewItem> GetTreeViewItems(bool includeCollapsedItems)
	{
		List<TreeViewItem> returnItems = new List<TreeViewItem>();

		for (int index = 0; index < this.InnerTreeView.Items.Count; index++)
		{
			TreeViewItem item = (TreeViewItem)this.InnerTreeView.ItemContainerGenerator.ContainerFromIndex(index);
			returnItems.Add(item);
			if (includeCollapsedItems || item.IsExpanded)
			{
				returnItems.AddRange(GetTreeViewItemItems(item, includeCollapsedItems));					
			}
		}

		return returnItems;
	}

	private static IEnumerable<TreeViewItem> GetTreeViewItemItems(TreeViewItem treeViewItem, bool includeCollapsedItems)
	{
		List<TreeViewItem> returnItems = new List<TreeViewItem>();

		for (int index = 0; index < treeViewItem.Items.Count; index++)
		{
			TreeViewItem item = (TreeViewItem)treeViewItem.ItemContainerGenerator.ContainerFromIndex(index);
			if (item != null)
			{
				returnItems.Add(item);
				if (includeCollapsedItems || item.IsExpanded)
				{
					returnItems.AddRange(GetTreeViewItemItems(item, includeCollapsedItems));
				}
			}
		}

		return returnItems;
	}

	#endregion
}
}