Question

I have a DataTemplate which contains a CheckBox and ListBox. When the CheckBox is checked, I want to change the ItemTemplate property on the ListBox to change the appearance of each item.

Right now, it looks like this:

<DataTemplate DataType={x:Type MyViewModel}>
   <DockPanel>       
      <CheckBox DockPanel.Dock="Bottom"
                Content="Show Details"
                HorizontalAlignment="Right"
                IsChecked="{Binding ShowDetails}" 
                Margin="0 5 10 5" />

      <ListBox ItemsSource="{Binding Items}"
               ItemTemplate="{StaticResource SimpleItemTemplate}"
               Margin="10 0 10 5">
         <ListBox.Triggers>
            <DataTrigger Binding="{Binding ShowDetails}" Value="True">
               <Setter Property="ItemTemplate"
                       Value="{StaticResource DetailedItemTemplate}" />
            </DataTrigger>
         </ListBox.Triggers>
      </ListBox>
   </DockPanel>
</DataTemplate>

However, when I try to compile, I get the following error messages:

Value ‘ItemTemplate’ cannot be assigned to property ‘Property’. Invalid PropertyDescriptor value.

and

Cannot find the static member ‘ItemTemplateProperty’ on the type ‘ContentPresenter’.

I’m still fairly new to WPF, so perhaps there is something I’m not quite understanding?

Answer 1

You need to do this through the ListBox Style rather than directly through its Triggers collection. A FrameworkElement’s Triggers collection can only contain EventTriggers (so I’m surprised your sample got as far as complaining about the properties!). Here’s what you need to do:

<ListBox ItemsSource="{Binding Items}">
  <ListBox.Style>
    <Style TargetType="ListBox">
      <Setter Property="ItemTemplate" Value="{StaticResource SimpleItemTemplate}" />
      <Style.Triggers>
        <DataTrigger Binding="{Binding ShowDetails}" Value="True">
           <Setter Property="ItemTemplate"
                   Value="{StaticResource DetailedItemTemplate}" />
        </DataTrigger>
     </Style.Triggers>
   </Style>
  </ListBox.Style>
</ListBox>