Hide the ToggleButton on WPF Expander via Binding

Question

I am trying to dynamically hide the Toggle Button on an Expander using a Property on my ViewModel set to the Visibility property. At least that is my thought. Is there a way to just alter that one setting on the ToggleButton control without having to do the ENTIRE template of the Toggle Button in my xaml?

Answer 1

You could use the Loaded event for the Expander and set up the Binding in the event handler or if you want a reusable way without code behind you could use an attached behavior.

The attached behavior finds the ToggleButton inside the Template and sets up the Binding to the attached property ToggleButtonVisibility.

Uploaded a sample app here: ExpanderToggleButtonVisibilityTest.zip

Use it like this

<Expander Name="expander"
          behaviors:ExpanderBehavior.BindToggleButtonVisibility="True"
          behaviors:ExpanderBehavior.ToggleButtonVisibility="{Binding YourVisibilityProperty}"
          .../>

ExpanderBehavior

public class ExpanderBehavior
{
    public static DependencyProperty BindToggleButtonVisibilityProperty =
        DependencyProperty.RegisterAttached("BindToggleButtonVisibility",
                                            typeof(bool),
                                            typeof(ExpanderBehavior),
                                            new PropertyMetadata(false, OnBindToggleButtonVisibilityChanged));

    public static bool GetBindToggleButtonVisibility(Expander expander)
    {
        return (bool)expander.GetValue(BindToggleButtonVisibilityProperty);
    }
    public static void SetBindToggleButtonVisibility(Expander expander, bool value)
    {
        expander.SetValue(BindToggleButtonVisibilityProperty, value);
    }

    private static void OnBindToggleButtonVisibilityChanged(DependencyObject target, DependencyPropertyChangedEventArgs e)
    {
        Expander expander = target as Expander;
        if (expander.IsLoaded == true)
        {
            BindToggleButtonVisibility(expander);
        }
        else
        {
            RoutedEventHandler loadedEventHandler = null;
            loadedEventHandler = new RoutedEventHandler(delegate
            {
                BindToggleButtonVisibility(expander);
                expander.Loaded -= loadedEventHandler;
            });
            expander.Loaded += loadedEventHandler;
        }
    }

    private static void BindToggleButtonVisibility(Expander expander)
    {
        ToggleButton headerSite = expander.Template.FindName("HeaderSite", expander) as ToggleButton;
        if (headerSite != null)
        {
            Binding visibilityBinding = new Binding
            {
                Source = expander,
                Path = new PropertyPath(ToggleButtonVisibilityProperty)
            };
            headerSite.SetBinding(ToggleButton.VisibilityProperty, visibilityBinding);
        }
    }

    #region ToggleButtonVisibilityProperty

    public static DependencyProperty ToggleButtonVisibilityProperty = 
        DependencyProperty.RegisterAttached("ToggleButtonVisibility",
                                            typeof(Visibility),
                                            typeof(ExpanderBehavior),
                                            new PropertyMetadata(Visibility.Visible));

    public static Visibility GetToggleButtonVisibility(Expander expander)
    {
        return (Visibility)expander.GetValue(ToggleButtonVisibilityProperty);
    }
    public static void SetToggleButtonVisibility(Expander expander, Visibility value)
    {
        expander.SetValue(ToggleButtonVisibilityProperty, value);
    }

    #endregion // ToggleButtonVisibilityProperty
}