How do I obtain the Index of a ListViewItem? - wpf

Question

I have a list view that uses a collectionsource and wish to set the background colour of the ListViewItems depending upon whether their index in the list matches a value held in the view model. To do this I am binding the background of the listVeiwItem to the value in the ViewModel, and using a converter to determine the background colour. To make this determination the converter needs to be passed the ListViewItem's index. How do I obtain the index using XAML?
Here is the XAML for the data template used by the ListView:
<DataTemplate x:Key="ILMemberTemplate">
<StackPanel Orientation="Horizontal" Background="{Binding Path=ListIndex, Mode=OneWay, Converter={StaticResource ParticipantBackground}, ConverterParameter={???}}">
<TextBlock
Width="200"
TextAlignment="Left"
Foreground="{Binding Path=IsPC, Mode=OneWay, Converter={StaticResource ParticipantColour}}"
Text="{Binding Path=Name, Mode=OneWay}"/>
<TextBlock
Width="40"
TextAlignment="Center"
Foreground="{Binding Path=IsPC, Mode=OneWay, Converter={StaticResource ParticipantColour}}"
Text="{Binding Path=Initiative, Mode=OneWay}"/>
</StackPanel>
</DataTemplate>

Answer 1

You can't obtain the index in XAML and pass it as a ConverterParameter. This is not possible. But you can use a multi converter and bind to both the ListIndex and the parent ListViewItem container, e.g.:
class MultiConverter : IMultiValueConverter
{
public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
{
var listIndex = values[0];
//...
ListViewItem item = value as ListViewItem;
ListView lv = FindParent<ListView>(item);
ICollectionView view = lv.ItemsSource as ICollectionView;
IEnumerator e = view.GetEnumerator();
int index = 0;
while (e.MoveNext())
{
if (Equals(item.DataContext, e.Current))
return index;
else
index++;
}
//return some brush based on the indexes..
}
public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture)
{
throw new NotSupportedException();
}
private static T FindParent<T>(DependencyObject dependencyObject) where T : DependencyObject
{
var parent = VisualTreeHelper.GetParent(dependencyObject);
if (parent == null) return null;
var parentT = parent as T;
return parentT ?? FindParent<T>(parent);
}
}
XAML:
<DataTemplate x:Key="ILMemberTemplate">
<StackPanel Orientation="Horizontal">
<StackPanel.Background>
<MultiBinding Converter="{StaticResource multiConverter}">
<Binding Path="ListIndex" />
<Binding Path="." RelativeSource="{RelativeSource AncestorType=ListViewItem}" />
</MultiBinding>
</StackPanel.Background>
<!-- ... -->
</StackPanel>
</DataTemplate>