WPF：如何在DockingManager中获取当前选项卡

Question

我在xaml中定义了一个动态DockingManager，当我打开多个标签时如何获取当前标签？

这是我定义DockingManager的方式：

    <xcad:DockingManager Name="DockingManager" 
                         DockPanel.Dock="Bottom"
                         AllowMixedOrientation="True"
                         BorderBrush="White"
                         BorderThickness="1" Grid.RowSpan="2">
        <xcad:DockingManager.Theme>
            <xcad:GenericTheme />
        </xcad:DockingManager.Theme>
        <xcad:DockingManager.DocumentHeaderTemplate>
            <DataTemplate>
                <StackPanel Orientation="Horizontal" ScrollViewer.HorizontalScrollBarVisibility="Auto">
                    <Image Source="{Binding IconSource}" Margin="0,0,4,0"/>
                    <TextBlock Text="{Binding Title}" />
                </StackPanel>
            </DataTemplate>
        </xcad:DockingManager.DocumentHeaderTemplate>
        <xcad:LayoutRoot x:Name="_layoutRoot">
            <xcad:LayoutPanel x:Name="tabs">
                <xcad:LayoutDocumentPaneGroup x:Name="tabGroup">
                    <xcad:LayoutDocumentPane x:Name="CanvasTabs" >

                    </xcad:LayoutDocumentPane>
                </xcad:LayoutDocumentPaneGroup>
            </xcad:LayoutPanel>
        </xcad:LayoutRoot>
    </xcad:DockingManager>