[WPF] Hide items with trigger in treeview

Question

Hi,

I've got a treeview, in which I use a HierarchicalDataTemplate. With this, I color my different items (all of the same type).

With a click on a checkbox in the Page, I want to hide some of the items (with a certain Property). I've tested many code, but nothing works properly. I'm looking for answers ...

Here's a sample of my code :

public partial class Window1 : Window
{
    public Window1()
    {
        InitializeComponent();

        TreeElements tRoot = new TreeElements("Root", false);
        TreeElements t1 = new TreeElements("Node 1", false);
        TreeElements t11 = new TreeElements("Node 1-1", true);
        t1.Children.Add(t11);
        TreeElements t12 = new TreeElements("Node 1-2", false);
        t1.Children.Add(t12);
        tRoot.Children.Add(t1);
        TreeElements t2 = new TreeElements("Node 2", false);
        TreeElements t21= new TreeElements("Node 2-1", false);
        TreeElements t211 = new TreeElements("Node 2-1-1", false);
        t21.Children.Add(t211);
        t2.Children.Add(t21);
        tRoot.Children.Add(t2);
        trv.Items.Add(tRoot);
    }
}

public class TreeElements
{
    public string Description { get; set; }
    public List<TreeElements> Children { get; set; }

    public TreeElements(string description, bool error)
    {
        Description = description;
        _error = error;
        Children = new List<TreeElements>();
    }

    private bool _error;

    public bool Error
    {
        get
        {
            bool bValue = _error;
            foreach (TreeElements child in Children)
                bValue = bValue || child.Error;
            return bValue;
        }
    }
}

And the XAML :

<Window x:Class="WpfApplication2.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Window1" Height="300" Width="300">

    <Window.Resources>
        <HierarchicalDataTemplate x:Key="HDT_items" ItemsSource="{Binding Path=Children}">
            <TextBlock Text="{Binding Path=Description}" x:Name="txt" />
            <HierarchicalDataTemplate.Triggers>
                <DataTrigger Binding="{Binding Path=Error}" Value="true">
                    <Setter TargetName="txt" Property="Foreground" Value="Red" />
                </DataTrigger>
            </HierarchicalDataTemplate.Triggers>
        </HierarchicalDataTemplate>    
    </Window.Resources>

    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto" />
            <RowDefinition Height="*" />
        </Grid.RowDefinitions>

        <CheckBox x:Name="chk">Mask some items</CheckBox>

        <TreeView Grid.Row="1" x:Name="trv" ItemTemplate="{StaticResource HDT_items}" />
    </Grid>
</Window>

I want, when the checkbox is checked, to not display the nodes who are with Error=false, but without changing the data source. Is it possible, and how ?

Answer 1

Hi Gulix.

Change type of TreeElement.Children from List to ObservableCollecton. And instead of hiding items in the view, simply remove tme from underlying collection in the ViewModel.