Question

I have a ListView declared as:

<ListView x:Name="Tree"
      ItemsSource="{Binding ElementName=This, Path=Some.Path.Values}"
      AlternationCount="2"
      ScrollViewer.CanContentScroll="False">

and a style defined as

<UserControl.Resources>
<Style TargetType="ListViewItem">
    <Style.Resources>
        <SolidColorBrush x:Key="{x:Static SystemColors.HighlightBrushKey}" Color="SteelBlue"/>
        <SolidColorBrush x:Key="{x:Static SystemColors.ControlBrushKey}" Color="Gray"/>
    </Style.Resources>
    <Style.Triggers>
        <Trigger Property="ItemsControl.AlternationIndex" Value="0">
            <Setter Property="Background" Value="White" />
        </Trigger>
        <Trigger Property="ItemsControl.AlternationIndex" Value="1">
            <Setter Property="Background" Value="GhostWhite" />
        </Trigger>
    </Style.Triggers>
    <Setter Property="HorizontalContentAlignment" Value="Stretch" />
    <Setter Property="VerticalContentAlignment" Value="Top" />
    <EventSetter Event="Loaded" Handler="ContinueLoading" />
</Style>

This combination produced the original desired behaviour, which is that of alternating background highlights. The new desired behaviour was to change that background color depending on the value of a property of a given ListView item; as such the Style.Triggers was changed to

<Style.Triggers>
    <Trigger Property="ItemsControl.AlternationIndex" Value="0">
        <Setter Property="Background" Value="White" />
    </Trigger>
    <Trigger Property="ItemsControl.AlternationIndex" Value="1">
        <Setter Property="Background" Value="GhostWhite" />
    </Trigger>
    <MultiDataTrigger>
        <MultiDataTrigger.Conditions>
            <Condition Binding="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type ContentPresenter}}, Path=(ItemsControl.AlternationIndex)}" Value="0"/>
            <Condition Binding="{Binding Converter={x:Static controls:Converters.ObjectType}}" Value="{x:Type client:DocumentEntryTypeA}" />
        </MultiDataTrigger.Conditions>
        <Setter Property="Background" Value="{Binding Converter={x:Static controls:Converters.LightColor}, UpdateSourceTrigger=PropertyChanged, Path=Status}" />
    </MultiDataTrigger>
    <MultiDataTrigger>
        <MultiDataTrigger.Conditions>
            <Condition Binding="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type ContentPresenter}}, Path=(ItemsControl.AlternationIndex)}" Value="1"/>
            <Condition Binding="{Binding Converter={x:Static controls:Converters.ObjectType}}" Value="{x:Type client:DocumentEntryTypeA}" />
        </MultiDataTrigger.Conditions>
        <Setter Property="Background" Value="{Binding Converter={x:Static controls:Converters.DarkColor}, UpdateSourceTrigger=PropertyChanged, Path=Status}" />
    </MultiDataTrigger>
</Style.Triggers>
</UserControl.Resources>

The ObjectType Converter checks that an element is of a given class; the LightColor and DarkColor Converters produce the selected background values depending on the value of the Status property.

The issue with this code is that the binding I use seems to always produce an AlternationIndex value of ‘0’, i.e. the Converter LightColor is used for every entry. In addition to the code above, I have also tried the following bindings with the same result:

<Condition Binding="{Binding RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=ItemsControl}, Path=AlternationIndex}" Value="0"/>
<Condition Binding="{Binding RelativeSource={RelativeSource AncestorType={x:Type ListView}}, Path=(ItemsControl.AlternationIndex)}" Value="0"/>

Based on the examples I’ve seen most of the solutions don’t separate the style from the object; in my case the style is defined separately within UserControl.Resources. However, since using a Trigger works fine, I’m not sure why a DataTrigger does not, or what would be required to get it working.

Answer 1

The first condition in your MultiDataTrigger finds the most recent ContentPresenter, and tries to bind to ContentPresenter.ItemsControl.AlternationIndex, and ItemsControl.AlternationIndex is not a valid property for ContentPresenter.

Try changing that to RelativeSource={RelativeSource Self} so you will be binding to the ItemsControl.AlternationIndex of the current object