#1,002 – Using Larger Values for AlternationCount in an ItemsControl

The AlternationCount and AlternationIndex properties of controls inheriting from ItemsControl allow setting property values that alternate across the collection of items.

An alternation count of two allows you to apply a style that affects every other item in a list.  Higher values allow a longer sequence of items before a particular pattern repeats.

In the example below, we set the Background color of each item differently.  The pattern repeats after every fourth item because the AlternationCount is set to 4.

    <Window.Resources>
        <AlternationConverter x:Key="altconvBackground">
            <SolidColorBrush Color="Azure"/>
            <SolidColorBrush Color="LightGreen"/>
            <SolidColorBrush Color="LightPink"/>
            <SolidColorBrush Color="Thistle"/>
        </AlternationConverter>
    </Window.Resources>

    <Grid Margin="10" >
        <ListBox ItemsSource="{Binding ActorList}" Width="200"
                 AlternationCount="4">
            <ListBox.ItemContainerStyle>
                <Style TargetType="{x:Type ListBoxItem}">
                    <Setter Property="Background"
                            Value="{Binding RelativeSource={RelativeSource Self}, Path=(ItemsControl.AlternationIndex), Converter={StaticResource altconvBackground}}"/>
                </Style>
            </ListBox.ItemContainerStyle>
        </ListBox>
    </Grid>

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