有两个循环的树枝（非symfony）(Twig with two loops (non-symfony))

 你可以用触发器来做到这一点： 
 
<ComboBox.ItemTemplate>
  <DataTemplate>
    <StackPanel Orientation="Horizontal">
      <TextBlock Text="{Binding Piece.NoPiece}" Width="50" x:Name="Column1" />
      <TextBlock Text="{Binding Piece.Description}" Width="170" />
      <TextBlock Text="{Binding Piece.Categorie.NomCategorie}" x:Name="Column3" />
    </StackPanel>
    <DataTemplate.Triggers>
      <!-- This trigger fires for the selected item in the drop-down list -->
      <DataTrigger Binding="{Binding 
                       RelativeSource={RelativeSource Mode=FindAncestor, 
                                                      AncestorType=ComboBoxItem},
                       Path=IsSelected}" 
        Value="True">
        <Setter TargetName="Column1" Property="Visibility" Value="Hidden" />
        <Setter TargetName="Column3" Property="Visibility" Value="Hidden" />
      </DataTrigger>

      <!-- This trigger fires for the selected item (ie the one that's
           visible when the popup is closed -->
      <DataTrigger Binding="{Binding 
                       RelativeSource={RelativeSource Mode=FindAncestor, 
                                                      AncestorType=ComboBoxItem}}"
                   Value="{x:Null}">
        <Setter TargetName="Column1" Property="Visibility" Value="Hidden" />
        <Setter TargetName="Column3" Property="Visibility" Value="Hidden" />
      </DataTrigger>
    </DataTemplate.Triggers>
  </DataTemplate>
</ComboBox.ItemTemplate>
 
 编辑 
 
 我更新了XAML以展示如何在弹出窗口被折叠时将替代格式应用于所选项目（我不确定该区域被称为什么）。 
 
 诀窍是下拉区域中的项目包含在逻辑树中的ComboBoxItem对象中。 RelativeSource绑定查找该类型的对象作为祖先。 
 
 
 
 如果它发现它，它假定该项目在树中（并检查它是否被选中） 
 
 
 如果找不到（ null ）则它假定该项目位于组合框区域而不是弹出窗口 
 
 
 如果你以某种方式在另一个组合框的项模板中有一个组合框，这将会崩溃。 我不认为我想使用那个UI！ 

You can do it with triggers:
 
<ComboBox.ItemTemplate>
  <DataTemplate>
    <StackPanel Orientation="Horizontal">
      <TextBlock Text="{Binding Piece.NoPiece}" Width="50" x:Name="Column1" />
      <TextBlock Text="{Binding Piece.Description}" Width="170" />
      <TextBlock Text="{Binding Piece.Categorie.NomCategorie}" x:Name="Column3" />
    </StackPanel>
    <DataTemplate.Triggers>
      <!-- This trigger fires for the selected item in the drop-down list -->
      <DataTrigger Binding="{Binding 
                       RelativeSource={RelativeSource Mode=FindAncestor, 
                                                      AncestorType=ComboBoxItem},
                       Path=IsSelected}" 
        Value="True">
        <Setter TargetName="Column1" Property="Visibility" Value="Hidden" />
        <Setter TargetName="Column3" Property="Visibility" Value="Hidden" />
      </DataTrigger>

      <!-- This trigger fires for the selected item (ie the one that's
           visible when the popup is closed -->
      <DataTrigger Binding="{Binding 
                       RelativeSource={RelativeSource Mode=FindAncestor, 
                                                      AncestorType=ComboBoxItem}}"
                   Value="{x:Null}">
        <Setter TargetName="Column1" Property="Visibility" Value="Hidden" />
        <Setter TargetName="Column3" Property="Visibility" Value="Hidden" />
      </DataTrigger>
    </DataTemplate.Triggers>
  </DataTemplate>
</ComboBox.ItemTemplate>
 
EDIT
 
I've updated the XAML to show how to apply the alternative formatting to the selected item when the popup is collapsed (I'm not sure what that area is called.)
 
The trick is that items in the drop-down area are contained within ComboBoxItem objects in the logical tree. The RelativeSource binding looks for an object of that type as an ancestor.
 
 
 
If it finds it, it assumes that the item is in the tree (and checks whether it's selected)
 
 
If it's not found (null) then it assumes the item is in the combo box area rather than the popup
 
 
This would fall apart if you, somehow, had a combo box within the item template of another combo box. I don't think I'd like to use that UI though!