Style Nth item in ItemsControl - wpf

Question

I have an ItemsControl with an associated DataTemplate as below. My question is how can I style the Nth item in the ItemsControl differently? I am trying to place borders on certain items only.
<DataTemplate x:Key="CTemplate">
<Grid HorizontalAlignment="Left" Width="200" Height="Auto" Margin="0,0,30,30">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="Auto"/>
<ColumnDefinition Width="10"/>
<ColumnDefinition Width="*"/>
</Grid.ColumnDefinitions>
<StackPanel Orientation="Vertical" Grid.Column="0">
<TextBlock Text="Device Name:" Style="{StaticResource i2_TB}"/>
<TextBlock Text="Device ID:" Style="{StaticResource i2_TB}" />
</StackPanel>
<StackPanel Orientation="Vertical" Grid.Column="2">
<TextBlock Text="{Binding DeviceName}" Style="{StaticResource i2_TB}" TextTrimming="CharacterEllipsis" />
<TextBlock Text="{Binding DeviceID}" Style="{StaticResource i2_TB}" TextTrimming="CharacterEllipsis" />
</StackPanel>
</Grid>
</DataTemplate>

Answer 1

I figured it out and its pretty simple
Firstly set an AlternationCount that matches your N. In my case I had 3 items per row and I wanted the 3rd one to be different.
<ItemsControl ItemTemplate="{StaticResource CTemplate}" AlternationCount="3">
Secondly set up your data triggers in the template itself, using the AlternationIndex as the data trigger
<DataTemplate.Triggers>
<Trigger Property="ItemsControl.AlternationIndex" Value="2">
<Setter Property="BorderThickness" Value="0,0,0,1" TargetName="controlHost"/>
</Trigger>
</DataTemplate.Triggers>
Win

Answer 2

I can think of 3 ways of doing this.
1st way
Have a simple property on the things you want to Template, then have a TemplateSelector that will pick correct template based on that property
2nd way
Or you could use a combination of TemplateSelector and ItemContainerGenerator.IndexFromContainer where you use the container and item in TemplateSelector to get index and return correct DataTemplate
3rd way
Or another idea may lie in the use of a ValueConverter/MarkupExtension.
You may need to have a MultiValueConverter setup something like this
Item[0] : DataTemplate standard resource
Item[1] : Alternative DataTemplate resource
Item[2] : The listbox (relative source lookup)
Item[3] : The listboxitem (relative source lookup)
Then you can use the ItemContainerGenerator.IndexFromContainer, and then just return the DataTemplate that matches the index.
I did something like this once. I think it was in this code :
http://www.codeproject.com/Articles/30021/WPF-Sticky-Notes-ListBox

Answer 3

If your items are of different types, then it could be as easy as providing a DataTemplate with no x:Key value set on them for each of the different types:
<DataTemplate DataType="{x:Type DataTypes:ThisType}">
...
</DataTemplate>
<DataTemplate DataType="{x:Type DataTypes:ThatType}">
...
</DataTemplate>
However, if your items are all of the same type then the standard way to do this is to create a named DataTemplate for each of the different looks that you want and to use a DataTemplateSelector. In the DataTemplateSelector.SelectTemplate method, you can decide which DataTemplate to display for each item:
public class TaskListDataTemplateSelector : DataTemplateSelector
{
public override DataTemplate SelectTemplate(object item, DependencyObject container)
{
FrameworkElement element = container as FrameworkElement;
if (element != null && item != null && item is Task)
{
Task taskitem = item as Task;
if (taskitem.Priority == 1) return element.FindResource(
"importantTaskTemplate") as DataTemplate;
else return element.FindResource("myTaskTemplate") as DataTemplate;
}
return null;
}
}
Example taken from the linked page (below) on MSDN
You can find out more from the DataTemplateSelector Class page on MSDN.