Using the Treeview HierarchicalDataTemplate.Triggers to change folder icon

Question

I'm pretty fresh to WPF and this is the closest I have come to achieving what I set out to do after reviewing many of the previously asked questions posted here. The XAML code:

<TreeView x:Name="folderView" Grid.Column="0" Grid.Row="1" BorderThickness="0">
    <TreeViewItem Header="Folders" ItemsSource="{Binding SubFolders, Source={StaticResource RootFolderDataProvider}}" Margin="5"/>

    <TreeView.Resources>
        <HierarchicalDataTemplate DataType="{x:Type my:FolderView}" ItemsSource="{Binding SubFolders}">
            <StackPanel Orientation="Horizontal" Name="myPanel">
                <Image x:Name="img" Width="16" Height="16" Source="Images/FolderClosed.png" />
                <TextBlock Text="{Binding Name}" />
            </StackPanel>

            <HierarchicalDataTemplate.Triggers>
                <DataTrigger Binding="{Binding IsExpanded}" Value="True">
                    <Setter TargetName="img" Property="Source" Value="Images/FolderOpen.png"/>
                </DataTrigger>
            </HierarchicalDataTemplate.Triggers>
        </HierarchicalDataTemplate>    
    </TreeView.Resources>
</TreeView>

This displays the FolderClosed image on all my subfolders except the very top root folder. The HierachicalDataTemplate trigger also fails to fire when expanded. Any help would be appreciated.

Answer 1

If you are binding to the TreeViewItem IsExpanded property, then you will have to update your binding like:

<DataTrigger Binding="{Binding IsExpanded, RelativeSource={RelativeSource AncestorType={x:Type TreeViewItem}}}" Value="True">
   <Setter TargetName="img" Property="Source" Value="Images/FolderOpen.png"/>
</DataTrigger>

Answer 2

I cannot pin point the issues. But as a first step you should check if the binding is working or not. you can add debugging for binding as mentioned in here

eg :

<Window 
    xmlns:diag="clr-namespace:System.Diagnostics;assembly=WindowsBase"
    xmlns:local="clr-namespace:DebugDataBindings"
    x:Class="DebugDataBindings.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="MainWindow" Height="350" Width="525">
    <Grid x:Name="layoutRoot">
        <Grid.Resources>
            <local:DebugConverter x:Key="debugConverter" /> 
        </Grid.Resources>
        <TextBox 
            Text="{Binding Path=Customer.FirstName, diag:PresentationTraceSources.TraceLevel=High}"   
            Height="23" HorizontalAlignment="Left" Margin="90,18,0,0" VerticalAlignment="Top" Width="120"/>
    </Grid>
</Window>