wpf combobox with custom itemtemplate text

Question

I have ComboBox with custom ItemTemplate .

<ComboBox Height="20" Width="200" 
          SelectedItem="{Binding Path=SelectedDesign}"
          ItemsSource="{Binding Path=Designs}" HorizontalAlignment="Left" 
          ScrollViewer.CanContentScroll="False">

    <ComboBox.ItemTemplate>
        <DataTemplate DataType="{x:Type formdesign:FormDesignContainer}">
            <Rectangle Width="200" Height="100">
                <Rectangle.Fill>
                    <ImageBrush ImageSource="{Binding Path=ImageThumb}" Stretch="Uniform" />
                </Rectangle.Fill>
            </Rectangle>
        </DataTemplate>
    </ComboBox.ItemTemplate>

</ComboBox>

This works well. However WPF tries to draw rectangle as Combobox Text. How can I set "text" for this template. By "text" I mean string or control which represent selected item and write into combobox when item is selected

In other words I'd like to do this:

But now I got this

Answer 1

Try setting SelectionBoxItemTemplate with a TextBlock. Appears that SelectionBoxItemTemplate is read-only. So another approach is to override ItemContainerStyle.Template. Example

Answer 2

I found this solution by Ray Burns a good approach. You can define two DataTemplate one for Items in the drop down list and the other for the selected item which should be shown in the Combobox . The using a trigger and checking the visual tree it decide which one to use.

<Window.Resources>    
  <DataTemplate x:Key="NormalItemTemplate" ...>
    ...
  </DataTemplate>

  <DataTemplate x:Key="SelectionBoxTemplate" ...>
    ...
  </DataTemplate>

  <DataTemplate x:Key="CombinedTemplate">
    <ContentPresenter x:Name="Presenter"
       Content="{Binding}"
       ContentTemplate="{StaticResource NormalItemTemplate}" />
    <DataTemplate.Triggers>
      <DataTrigger
        Binding="{Binding RelativeSource={RelativeSource FindAncestor,ComboBoxItem,1}}"
        Value="{x:Null}">
        <Setter TargetName="Presenter" Property="ContentTemplate"
                Value="{StaticResource SelectionBoxTemplate}" />
      </DataTrigger>
    </DataTemplate.Triggers>
  </DataTemplate>

</Window.Resources>

...

<ComboBox
  ItemTemplate="{StaticResource CombinedTemplate}"
  ItemsSource="..."/>

Answer 3

将Textblock添加到datatemplate并绑定它或在矩形上添加Contentpersenter编辑：看起来我没有得到你要完成的任务，