ItemsControl with two DataTemplates using AlternationIndex trigger, XAML - wpf

Question

I have a user control with a items control and I would like it to have 2 completely different item template styles depending on the alternation index. I've seen lots of tutorials on how to change the background colour based on the index but not changing the style on each index. Here's what I have so far.
Defined templates:
<UserControl.Resources>
<DataTemplate x:Key="ItemLeft" >
<Border Background="Blue" Height="10">
<!-- Define Left Style -->
</Border>
</DataTemplate>
<DataTemplate x:Key="ItemRight">
<Border Background="Red" Height="10">
<!-- Define Right Style -->
</Border>
</DataTemplate>
</UserControl.Resources>
I've removed the data template code to make it easier to read. It's a lot more than border colours.
Items Control:
<ItemsControl Name="ItemControl" AlternationCount="2">
<ItemsControl.ItemsPanel>
<ItemsPanelTemplate>
<VirtualizingStackPanel IsItemsHost="True"/>
</ItemsPanelTemplate>
</ItemsControl.ItemsPanel>
<ItemsControl.Style>
<Style>
<Style.Triggers>
<Trigger Property="ItemsControl.AlternationIndex" Value="0">
<Setter Property="ItemsControl.ItemTemplate" Value="{StaticResource ItemRight}"/>
</Trigger>
<Trigger Property="ItemsControl.AlternationIndex" Value="1">
<Setter Property="ItemsControl.ItemTemplate" Value="{StaticResource ItemLeft}"/>
</Trigger>
</Style.Triggers>
</Style>
</ItemsControl.Style>
</ItemsControl>
I'm pretty sure I shouldn't be doing this type of trigger in the style but I'm not sure how else to do it. I'm new to using WPF, I've found most of it pretty intuitive but I'm lost here. I would like to try and contain this to just XAML code.
Thanks

Answer 1

ItemTemplate applies to all items. What you can do is use ContentControl as ItemTemplate with custom style that chooses ContentTemplate based on ItemsControl.AlternationIndex
<ItemsControl Name="ItemControl" AlternationCount="2">
<ItemsControl.ItemsPanel>
<ItemsPanelTemplate>
<VirtualizingStackPanel IsItemsHost="True"/>
</ItemsPanelTemplate>
</ItemsControl.ItemsPanel>
<ItemsControl.ItemTemplate>
<DataTemplate>
<ContentControl Content="{Binding}">
<ContentControl.Style>
<Style TargetType="{x:Type ContentControl}">
<Setter Property="ContentTemplate" Value="{StaticResource ItemLeft}"/>
<Style.Triggers>
<DataTrigger Binding="{Binding RelativeSource={RelativeSource Mode=FindAncestor,AncestorType={x:Type ContentPresenter}}, Path=(ItemsControl.AlternationIndex)}" Value="1">
<Setter Property="ContentTemplate" Value="{StaticResource ItemRight}"/>
</DataTrigger>
</Style.Triggers>
</Style>
</ContentControl.Style>
</ContentControl>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>

Answer 2

A simpler solution would be to set the ItemContainerStyle, and use a Trigger instead of a DataTrigger for the AlternationIndex:
<ItemsControl ... AlternationCount="2">
<ItemsControl.ItemContainerStyle>
<Style TargetType="ContentPresenter">
<Setter Property="ContentTemplate" Value="{StaticResource ItemLeft}"/>
<Style.Triggers>
<Trigger Property="ItemsControl.AlternationIndex" Value="1">
<Setter Property="ContentTemplate"
Value="{StaticResource ItemRight}"/>
</Trigger>
</Style.Triggers>
</Style>
</ItemsControl.ItemContainerStyle>
...
</ItemsControl>