为什么不能操作ControlTemplate

后代码：

var roomTable = from desks in context.RoomToStandartDesks
            where desks.id_room == room.id
            select desks.Desk;
var tabItem = new TabItem
          {
          DataContext = roomTable,
          Header = headerText,
          };
if (controlTemplate == null)
    tabItem.Content = (object)roomTable;
else
    tabItem.Content = new ContentControl { Template = controlTemplate };
tabItems.Add(tabItem);

((ContentControl)(tabItem.Content)).Content==空

((ContentControl)(((ContentControl)(tabItem)).Content)).ContentTemplate==空

和xaml控制模板：

<ControlTemplate x:Key="MyTabItemContentTemplate">
<StackPanel>
    <TextBlock Text="{Binding Path=x}"/>
    <ItemsControl ItemsSource="{Binding DataContext, Converter={StaticResource KeySimplyConvert}}">
        <ItemsControl.ItemsPanel>
        <ItemsPanelTemplate>
            <Canvas Margin="10" Background="AliceBlue"  HorizontalAlignment="Stretch" VerticalAlignment="Stretch"/>
        </ItemsPanelTemplate>
        </ItemsControl.ItemsPanel>
        <ItemsControl.ItemTemplate>
        <DataTemplate>
            <Border>
            <Border.RenderTransform>
                <TranslateTransform X="{Binding x, Mode=TwoWay}" Y="{Binding y, Mode=TwoWay}"/>
            </Border.RenderTransform>
            <Managerer:TablePanel DataContext="{Binding}" />
            </Border>
        </DataTemplate>
        </ItemsControl.ItemTemplate>
    </ItemsControl>
</StackPanel>
</ControlTemplate>

为什么？A使用Silverlight 4。