Binding Converter doesn't apply on root TreeViewItem element (WPF)

Question

I'm creating a file explorer app using the TreeView control provided by WPF. I've customized it such that it displays a file icon next to the path. I'm using a IValueConverter to convert the path to the required image, which I based off this page: http://www.codeproject.com/Articles/21248/A-Simple-WPF-Explorer-Tree

It mostly works! Except that the root TreeViewItems don't display icons for some reason. I placed a breakpoint on the IValueConverter::Convert() function and confirmed that it doesn't get executed for the root nodes, but do for all children nodes after that.

The VS output window shows no binding errors, so I'm at a loss at how this could happening. Any ideas?

Converter Code:

[ValueConversion(typeof(string), typeof(bool))]
public class HeaderToImageConverter : IValueConverter
{
    public static HeaderToImageConverter Instance = new HeaderToImageConverter();

    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        if ((value as string).Contains(@"\"))
        {
            Uri uri = new Uri("pack://application:,,,/Images/diskdrive.png");
            BitmapImage source = new BitmapImage(uri);
            return source;
        }
        else
        {
            Uri uri = new Uri("pack://application:,,,/Images/folder.png");
            BitmapImage source = new BitmapImage(uri);
            return source;
        }
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        throw new NotSupportedException("Cannot convert back");
    }
}

TreeView XAML:

<TreeView Grid.Column="0" Name="fileExplorer" Margin="8,8,8,8">
    <TreeView.Resources>
        <Style TargetType="{x:Type TreeViewItem}">
            <Setter Property="HeaderTemplate">
                <Setter.Value>
                    <DataTemplate>
                        <StackPanel Orientation="Horizontal">
                            <Image Width="20" Height="20" Stretch="Fill" Source="{Binding Converter={x:Static local:HeaderToImageConverter.Instance}}" />
                            <TextBlock Text="{Binding}" Margin="5,0" VerticalAlignment="Center"/>
                        </StackPanel>
                    </DataTemplate>
                </Setter.Value>
            </Setter>
        </Style>
    </TreeView.Resources>

Answer 1

I ran into a similar problem. But besides the TreeView.Resources I had the TreeView.ItemContainerStyle element as well. Moving the Style element to there actually styled only the root, but not the children. Therefore, a solution would be to put the element in both places.

TreeView XAML:

<TreeView Grid.Column="0" Name="fileExplorer" Margin="8,8,8,8">
    <TreeView.ItemContainerStyle>
        <Style TargetType="{x:Type TreeViewItem}">
            <Setter Property="HeaderTemplate">
                <Setter.Value>
                    <DataTemplate>
                        <StackPanel Orientation="Horizontal">
                            <Image Width="20" Height="20" Stretch="Fill" Source="{Binding Converter={x:Static local:HeaderToImageConverter.Instance}}" />
                            <TextBlock Text="{Binding}" Margin="5,0" VerticalAlignment="Center"/>
                        </StackPanel>
                    </DataTemplate>
                </Setter.Value>
            </Setter>
        </Style>
    </TreeView.ItemContainerStyle>
    <TreeView.Resources>
        <Style TargetType="{x:Type TreeViewItem}">
            <Setter Property="HeaderTemplate">
                <Setter.Value>
                    <DataTemplate>
                        <StackPanel Orientation="Horizontal">
                            <Image Width="20" Height="20" Stretch="Fill" Source="{Binding Converter={x:Static local:HeaderToImageConverter.Instance}}" />
                            <TextBlock Text="{Binding}" Margin="5,0" VerticalAlignment="Center"/>
                        </StackPanel>
                    </DataTemplate>
                </Setter.Value>
            </Setter>
        </Style>
    </TreeView.Resources>

Now, it would be nicer not to have to reuse this HeaderTemplate Setter. But I have not found a way to do this.