or
<DataTemplate x:Key="ComboBoxEditor"> <telerik:RadComboBox SelectedValue="{Binding Value, Mode=TwoWay, FallbackValue=null}" MinWidth="100" /></DataTemplate><telerik:RadPropertyGrid Name="_rpgTranslation" Grid.Row="1" AutoGenerateBindingPaths="True" telerik:StyleManager.Theme="Expression_Dark"/><telerik:RadGridView Name="gdTestRecords" DockPanel.Dock="Bottom" AutoGenerateColumns="False" ClipboardCopyMode ="All" MouseDoubleClick="gdTestRecords_MouseDoubleClick" SelectionMode="Extended" SelectionUnit="FullRow" MaxHeight="600" ScrollViewer.VerticalScrollBarVisibility="Visible"><UserControl x:Class="Company.KendoJavaScriptExtension.MyControl" xmlns:telerik="http://schemas.telerik.com/2008/xaml/presentation" xmlns:local="clr-namespace:Company.KendoJavaScriptExtension" mc:Ignorable="d" d:DesignHeight="300" d:DesignWidth="300" Name="MyToolWindow" Loaded="MyToolWindow_Loaded"> <Grid x:Name="LayoutRoot"> <Grid.Resources> <DataTemplate x:Key="comboboxTemplate"> <telerik:RadComboBox /> </DataTemplate> </Grid.Resources> <telerik:RadPropertyGrid x:Name="propertyGrid" Loaded="propertyGrid_Loaded" /> </Grid></UserControl>this.propertyGrid.PropertyDefinitions[5].EditorTemplate = LayoutRoot.Resources["comboboxTemplate"] as DataTemplate;