Alternating ListBox item background colours in WP7

I had a requirement today to implement alternating row colours in a Windows Phone 7 ListBox. After a bit of frustration with searching and only finding answers tht said “You can’t do it”, or that you need to add a property on the model to bind the background to, I eventually hit upon a nugget of common sense on this page.

Basically you need to create a converter class that will handle the alternation of backgrounds for you. It is ridiculously simple once you see it in action.

Step 1 : Create the converter.

public class AlternateRowColour : IValueConverter
{
bool isAlternate;
SolidColorBrush even = new SolidColorBrush(Colors.Transparent); // Set these two brushes to your alternating background colours.
SolidColorBrush odd = new SolidColorBrush(Color.FromArgb(255, 241, 241, 241));

public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
isAlternate = !isAlternate;
return isAlternate ? even : odd ;
}

public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
throw new NotImplementedException();
}
}

Step 2 : Add the converter to the page

<UserControl
 	...snip...
 	xmlns:conv="clr-namespace:MyApplication.Converters"
 	...snip...
 	>
	<UserControl.Resources>
		<conv:AlternateRowColour x:Key="RowColour" />
	</UserControl.Resources>
	...snip...
</UserControl>

Step 3 : Bind to the ListBox

<ListBox ItemsSource="{Binding}">
  <ListBox.ItemTemplate>
    <DataTemplate>
      <Grid Background="{Binding Converter={StaticResource RowColour}}">
        <!-- layout XAML -->
      </Grid>
    </DataTemplate>
  </ListBox.ItemTemplate>
</ListBox>

And you’re done.