MainWindow.xaml

<Window
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:dxmvvm="http://schemas.devexpress.com/winfx/2008/xaml/mvvm"
        xmlns:dxdiag="http://schemas.devexpress.com/winfx/2008/xaml/diagram" x:Class="CustomToolboxExample.MainWindow"
        mc:Ignorable="d"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition/>
            <ColumnDefinition Width="Auto"/>
        </Grid.ColumnDefinitions>
        <dxdiag:DiagramControl Grid.Row="0" Name="diagram"/>
        <ListBox x:Name="ShapeListBox" Tag="{Binding ElementName=diagram}" Grid.Column="1">
            <ListBox.ItemContainerStyle>
                <Style TargetType="ListBoxItem">
                    <Setter Property="FocusVisualStyle" Value="{x:Null}"/>
                    <Setter Property="dxmvvm:Interaction.BehaviorsTemplate">
                        <Setter.Value>
                            <DataTemplate>
                                <ItemsControl>
                                    <dxdiag:DiagramToolBehavior DiagramTool="{Binding}" Diagram="{Binding RelativeSource={RelativeSource AncestorType=ListBox}, Path=Tag}" />
                                </ItemsControl>
                            </DataTemplate>
                        </Setter.Value>
                    </Setter>
                </Style>
            </ListBox.ItemContainerStyle>
            <ListBox.ItemTemplate>
                <DataTemplate>
                    <dxdiag:ShapeToolboxPreview IsCompact="True"  ViewMode="IconsOnly" Diagram="{Binding ElementName=diagram}" ItemTool="{Binding}" Theme="{Binding ElementName=diagram, Path=Theme}"/>
                </DataTemplate>
            </ListBox.ItemTemplate>
        </ListBox>
    </Grid>
</Window>