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

February 5, 2014 Leave a comment

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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#1,001 – Setting an Alternating Background Color in an ItemsControl

February 4, 2014 1 Comment

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

The AlternationCount property dictates how many unique styles you alternate between.  The most common value is 2, indicating that every other item has a particular style.  In the example below, we use these properties to set up an alternating background color.

    <Window.Resources>
        <AlternationConverter x:Key="altconvBackground">
            <SolidColorBrush Color="AliceBlue"/>
            <SolidColorBrush Color="White"/>
        </AlternationConverter>
    </Window.Resources>

    <Grid Margin="10" >
        <ListBox ItemsSource="{Binding ActorList}" Width="200"
                 AlternationCount="2">
            <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>

We set an ItemContainerStyle because we want to set a property for a given ListBoxItem.  We then set the Background of each item to derive its value from the AlternationIndex property of the item.  The AlternationConverter is used to convert this index, 0 or 1, into a SolidColorBrush.

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