I had tried that approach to no avail. However, I did figure out order of events and was able to add code to the code behind to get it to work. Hopefully this will help someone else out as i saw this question posted several times without concrete solution.
I changed my bindings to the CheckState property (as opposed to isChecked property). Final XAML below:
<UserControl.Resources>
<!-- Page Converters -->
<converters:BooleanToToggleStateConverter x:Key="Bool2ToggleConverter" />
<telerik:ContainerBindingCollection x:Key="TreeBindings">
<telerik:ContainerBinding PropertyName="CheckState" Binding="{Binding IsChecked, Mode=TwoWay, Converter={StaticResource Bool2ToggleConverter}}" />
<telerik:ContainerBinding PropertyName="IsExpanded" Binding="{Binding IsExpanded, Mode=TwoWay}" />
</telerik:ContainerBindingCollection>
<telerik:HierarchicalDataTemplate x:Key="TreeItemTemplate" ItemsSource="{Binding Children}" telerik:ContainerBinding.ContainerBindings="{StaticResource TreeBindings}">
<StackPanel Orientation="Horizontal">
<TextBlock Text="{Binding DisplayName}" />
</StackPanel>
</telerik:HierarchicalDataTemplate>
</UserControl.Resources>
<Grid x:Name="LayoutRoot" Margin="10">
<Grid.RowDefinitions>
<RowDefinition Height="Auto"/>
<RowDefinition />
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="*"/>
</Grid.ColumnDefinitions>
<telerik:RadTreeView SelectionMode="Single" Grid.Row="1"
ItemTemplate="{StaticResource TreeItemTemplate}"
ItemsSource="{Binding ProcessTreeRoot}"
ItemPrepared="processSelectTree_ItemPrepared"
IsLoadOnDemandEnabled="True" LoadOnDemand="processSelectTree_LoadOnDemand"
ItemsOptionListType="CheckList"
IsOptionElementsEnabled="True"
PreviewUnchecked="processSelectTree_PreviewUnchecked"
IsExpandOnSingleClickEnabled="True"
telerik:ContainerBinding.ContainerBindings="{StaticResource TreeBindings}"
Checked="processSelectTree_Checked" Unchecked="processSelectTree_Checked"
Margin="0"
x:Name="processSelectTree"
IsTriStateMode="True" />
</Grid>
</UserControl>
The magic happens in my code behind. I set a flag to detect when a node is being expanded and not yet loaded. Since this event happens before the unwanted Unchecked event, I am able to use the PreviewUnchecked event to see if Im in this unwanted state. If I am, I simply throw that event away:
{
private bool bExpandingCheckedUnloadedItem_TelerikHack = false;
public DocumentAssignmentByProcess()
{
InitializeComponent();
}
private void processSelectTree_LoadOnDemand(object sender, Telerik.Windows.RadRoutedEventArgs e)
{
RadTreeViewItem treeitem = e.OriginalSource as RadTreeViewItem;
(DataContext as DocumentAssignmentByProcessViewModel).LoadChildrenOnDemandCommand.Execute(treeitem.Item as PlantConfigTreeItem);
// telerik tree hack. apparently if a node is checked (and not yet loaded), it will get unchecked when expanded
if (treeitem.CheckState == System.Windows.Automation.ToggleState.On)
{
treeitem.IsChecked = true;
bExpandingCheckedUnloadedItem_TelerikHack = true;
}
}
private void processSelectTree_ItemPrepared(object sender, Telerik.Windows.Controls.RadTreeViewItemPreparedEventArgs e)
{
RadTreeViewItem treeitem = (RadTreeViewItem)e.PreparedItem;
treeitem.IsLoadOnDemandEnabled = (treeitem.Item as PlantConfigTreeItem).HasChildren;
}
private void processSelectTree_PreviewUnchecked(object sender, Telerik.Windows.RadRoutedEventArgs e)
{
// more of the hack.. after the tree node is expanded, the tree control for some reason unselects the parent node
// this code checks for situatio where node was originally checked (indicated by bExpandingCheckedUnloadedItem)
// and will check it and cancel uncheck event
if (bExpandingCheckedUnloadedItem_TelerikHack)
{
bExpandingCheckedUnloadedItem_TelerikHack = false;
e.Handled = true;
RadTreeViewItem treeitem = e.OriginalSource as RadTreeViewItem;
treeitem.IsSelected = true;
}
}