WPF: Dynamically change ListBox's ItemTemplate based on ListBox Items Size

I need to change the DataTemplate of my ListBox, based on the ListBox items count. I have come up with the following XAML:

<Window.Resources>
  <DataTemplate x:Key="DefaultTemplate">
    <StackPanel Orientation="Horizontal">
   <TextBlock Text="{Binding Path=Text}"/>
   <TextBlock Text="default template" />
    </StackPanel>
  </DataTemplate>
  <DataTemplate x:Key="OtherTemplate">
    <StackPanel Orientation="Horizontal">
   <TextBlock Text="{Binding Path=Text}"/>
   <TextBlock Text="other template" />
    </StackPanel>
  </DataTemplate>      
</Window.Resources>
<ListBox Name="listBox1" ItemsSource="{Binding Path=Items}">
  <ListBox.Style>
    <Style TargetType="{x:Type ListBox}">
      <Setter Property="ItemTemplate" Value="{StaticResource DefaultTemplate}" />
        <Style.Triggers>
          <DataTrigger Binding="{Binding Path=Items.Count}" Value="1">
             <Setter Property="ItemTemplate" Value="{StaticResource OtherTemplate}"/>
          </DataTrigger>
        </Style.Triggers>
     </Style>
  </ListBox.Style>     
</ListBox>

With the above XAML, once I added two or more items to the bound list, the data template changed as expected (from other to default). However, if I remove the first item in the list with more than two items, the entire listbox just becomes empty (I verified that the bound list is non-empty). Removing the second item in a two items list works fine though (i.e. template changed from default to other).

Any ideas why this is happening? Or perhaps I went about the wrong way to solve this problem?开发者_JAVA百科

you could use data triggers, or you could use a DataTemplateSelector Here is an article that shows the basics. and here is the MSDN on applying it to the items control (also, a listbox)

I can't speak for the exact problem or the cause, but it is because a DataTrigger is setting a template when the count is 1 and only 1.

You can do 1 of 3 things to solve this problem, but only 1 I would recommend.

a) Implement your own DataTrigger by deriving from System.Windows.TriggerBase

b) Use an implementation of System.Windows.Data.IValueConverter that will convert from ItemsControl.Items.Count into a DataTemplate. Retrieve the templates by placing an element in scope of your resources as Binding.ConverterParameter, casting them to FrameWorkElement and call FrameWorkElement.FindResource().

C) This is my recommendation, write your own DataTemplateSelector to do the grunt work. This mechanism is specifically targeted at the functionality you with you achieve. I recently wrote one that will pick a DataTemplate based on the type of the source object without requiring a DataTemplate with no x:Key set. Using Properties on the template selector, you can pass DataTemplates into the DataTemplateSelector using XAML, removing that FindResource code 'todo' list.