RadTreeView provides check boxes displayed next to each item. In order to enable this behavior you need to set the IsOptionElementsEnabled property of the RadTreeView to True.

For example, add the following attribute to the treeview declaration in XAML:

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<telerik:RadTreeView x:Name="radTreeView" IsOptionElementsEnabled="True">

Here is a snapshot of the result.

You might want to enable check boxes in the code-behind. In order to do this, set the IsOptionElementsEnabled property of an instance of the RadTreeView class to True.

CopyC#

private void EnableCheckBoxes()
{
    radTreeView.IsOptionElementsEnabled = true;
}

CopyVB.NET

Private Sub EnableCheckBoxes()
    radTreeView.IsOptionElementsEnabled = True
End Sub

If you want your treeview to have check boxes with three states, then you need to set the IsTriStateMode property of the RadTreeView to True. When this mode is activated the CheckState property of each item depends on the CheckState property of its child items. In this mode the item will be checked only if all of its child items are checked too.

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<telerik:RadTreeView x:Name="radTreeView" IsOptionElementsEnabled="True" IsTriStateMode="True">

The result can be seen on the next figure:

The "Tri-state" behavior can be activated in the code-behind too. To do so, set the IsTriStateMode property of an instance of the RadTreeView class to True.

CopyC#

radTreeView.IsTriStateMode = true;

CopyVB.NET

radTreeView.IsTriStateMode = True

Important
Please keep in mind that the RadTreeView 'tri-state' check boxes logic is desined to work in declaratively populated RadTreeView control. This is why if your applicaiton implements an MVVM approach and the RadTreeView is databound, it's best to define custom 'tri-state' logic in your ViewModels following this tutorial.

To see the Item check state in the code-behind you should use the CheckState property of the RadTreeViewItem class. The CheckState property is a ToggleState enumeration and has the following values:

• On - the treeview item is checked.

• Off - the treeview item is not checked.

• Indeterminate - the treeview item has items that are checked and items that are not checked. This state is available only when the RadTreeViewIsTriStateMode property is set to True.

Note
The ToggleState enumeration is a part of the System.Windows.Automation namespace.

In order to access the initially checked item when the RadTreeViewIsTriStateMode property is set to True you should use the IsUserInitiated property of the RadTreeViewCheckEventArgs class. The IsUserInitiated property is a Boolean property that indicates whether the item is the initially checked one.

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private void RadTreeViewItem_Checked(object sender, Telerik.Windows.RadRoutedEventArgs e)
{
 bool isInitiallyChecked = (e as RadTreeViewCheckEventArgs).IsUserInitiated;
}

The RadTreeView and RadTreeViewItem classesoffer you four events for managing the changes of the item check state. These events are available both on the RadTreeView and on the RadTreeViewItem classes.

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<telerik:RadTreeView Margin="8" x:Name="radTreeView" IsOptionElementsEnabled="True"
        PreviewChecked="radTreeView_PreviewChecked"
        Checked="radTreeView_Checked"
        PreviewUnchecked="radTreeView_PreviewUnchecked"
        Unchecked="radTreeView_Unchecked">

The PreviewChecked event occurs when the treeview item is about to be checked. The Checked event is fired when the treeview item is already checked. The type of the passed event arguments for both of the events is RadRoutedEventArgs. In the event handlers you can place some code. For example, the following lines of code will set the foreground of the checked node green:

CopyC#

private void radTreeView_Checked( object sender, RadRoutedEventArgs e )
{
    ( e.Source as RadTreeViewItem ).Foreground = new SolidColorBrush( Colors.Green );
}

CopyVB.NET

Private Sub radTreeView_Checked(ByVal sender As Object, ByVal e As RadRoutedEventArgs)
    TryCast(e.Source, RadTreeViewItem).Foreground = New SolidColorBrush(Colors.Green)
End Sub

And here is the result:

The PreviewUnchecked event is fired when the treeview item is about to be unchecked. The Unchecked event occurs when the treeview item is unchecked. The type of the passed event arguments for both of the events is RadRoutedEventArgs.

Note
The RadRoutedEventArgs class is part of the Telerik.Windows namespace.

For a full list of the exposed by the RadTreeView event, please refer to the Events - Overview topic.