How to use the same DataTrigger for multiple DataTemplate?

Question

I want to set a DataTrigger for multiple DataTemplate but I am not sure if there is way to do that? I have view structured like below

<ItemsControl ItemsSource="{Binding Collection}"
              AlternationCount="2"
              ItemTemplateSelector="{StaticResource RowSelector}" >
<local:HeaderTemplateSelector x:Key="RowSelector"
            NormalTemplate="{StaticResource NormalTemplate}"
            ExpanderTemplate1="{StaticResource ExpanderTemplate1}"
            ExpanderTemplate2="{StaticResource ExpanderTemplate2}"
            ExpanderTemplate3="{StaticResource ExpanderTemplate3}"  />
<DataTemplate x:Key="NormalTemplate" ...>
    <stackpanel  x:Name="main"
<DataTemplate x:Key="ExpanderTemplate1" ...>
    <Grid  x:Name="main" ..>
<DataTemplate x:Key="ExpanderTemplate2" ...>
    <Expander  x:Name="main"
<DataTemplate x:Key="ExpanderTemplate3" ...>
    <Textblock  x:Name="main" ...>

I want this data trigger which provides alternative background for rows, the trigger defined below

<DataTemplate.Triggers>
    <Trigger Property="ItemsControl.AlternationIndex" Value="0">
        <Setter Property="Background" Value="Blue" TargetName="main"/>
    </Trigger>
    <Trigger Property="ItemsControl.AlternationIndex" Value="1">
        <Setter Property="Background" Value="black"  TargetName="main"/>
    </Trigger>
</DataTemplate.Triggers>

I can add this to the end of each DataTemplate and it works fine but it mean that I have to duplicate the some code 4 times, is there any way to avoid that? (I know I can use datagrid but it is overkill for this simple structure)

Maybe a dup of this: http://stackoverflow.com/questions/4443600/is-there-a-way-to-use-data-template-inheritance-in-wpf — Vlad, Oct 16 '12 at 16:11
maybe you can add the triggers to a style, not to a template? you can reuse the style or base a new style off the base one. — Vlad, Oct 16 '12 at 16:14
I don’t know any way to apply style here, because the trigger is based on “ItemsControl.AlternationIndex” which sets background so where can I apply Style in this case?! — Fred Jand, Oct 16 '12 at 16:46

score 3 · Accepted Answer · edited May 23 '17 at 12:04

You can try to set the trigger with the style:

<Style TargetType="Panel" x:Key="AlternatelyPainted">
    <Style.Triggers>
        <DataTrigger Binding="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type ContentPresenter}}, Path=(ItemsControl.AlternationIndex)}" Value="0">
            <Setter Property="Background" Value="Red"/>
        </DataTrigger>
        <DataTrigger Binding="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type ContentPresenter}}, Path=(ItemsControl.AlternationIndex)}" Value="1">
            <Setter Property="Background" Value="Blue"/>
        </DataTrigger>
    </Style.Triggers>
</Style>

(code thankfully stolen from this answer) and use it in your templates:

<DataTemplate x:Key="NormalTemplate" ...>
    <StackPanel Style="{StaticResource AlternatelyPainted}">
        ...
    </StackPanel>
</DataTemplate>

etc.

Edit: if you want the style to be universal, not Panel-specific, you can try the following trick:

<Style x:Key="AlternatelyPainted">
    <Style.Triggers>
        <DataTrigger Binding="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type ContentPresenter}}, Path=(ItemsControl.AlternationIndex)}" Value="0">
            <Setter Property="Panel.Background" Value="Red"/>
            <Setter Property="Control.Background" Value="Red"/>
            <Setter Property="TextBlock.Background" Value="Red"/>
        </DataTrigger>
        <DataTrigger Binding="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type ContentPresenter}}, Path=(ItemsControl.AlternationIndex)}" Value="1">
            <Setter Property="Panel.Background" Value="Blue"/>
            <Setter Property="Control.Background" Value="Blue"/>
            <Setter Property="TextBlock.Background" Value="Blue"/>
        </DataTrigger>
    </Style.Triggers>
</Style>

(removed the TargetType and added explicit types to the property names). Note that TextBlock doesn't inherit its Background, so we need an additional line for it.

It is ok for stackpanel and grid and other panel type elements. But this one has on problem, the type should be always Panel which is not true in my case, I have different types including controls like "Expander and "Textblock"! but I can wrap them in a panel at least as temporary a solution, it's better than duplication anyway, thanks. — Fred Jand, Oct 16 '12 at 18:39
this helps my special case, but I wonder why it is not possible to set triggers properties like style? — Fred Jand, Oct 21 '12 at 02:49

How to use the same DataTrigger for multiple DataTemplate?

1 Answers1