List of Expanders selectedItem issue

Question

Hi,
In my wpf application, I have a listbox containing expanders. To implement a scenario that only one expander can be expanded at a time, I have done below binding
<Style x:Key="LeftPanelExpanderStyle" TargetType="{x:Type Expander}">
<Setter
Property="IsExpanded"
Value="{Binding Path=IsSelected, RelativeSource={RelativeSource AncestorType={x:Type ListBoxItem}}}"/>
Suppose we have two expanders E1 and E2 in the listbox. When I expand E1, corresponding listboxitem is selected. When I expand E2 corresponding listboxitem is selected. But if I again click on E2, the listboxitem is unselected and now ListBox has no
selection.
Is there any way to keep the selection if the same expander is expanded and collapsed?
I want to switch the selection only when any other expander is clicked.
Regards,
Sharda.

Answer 1

>>But if I again click on E2, the listboxitem is unselected and now ListBox has no selection.
Since you bind the IsExpanded property of the IsSelected property of the ListBoxItem, the IsSelected property will be set to false whenever the IsExpanded property gets set to false. This is how it works so you cannot simply use a two-way binding here.
You could however write some code to get the desired behaviour. You could for example handle the Selected event of the ListBoxItem and the Expanded event of the Expander and set the IsSelected property and the IsExpanded property as appropriate. Here is
an example that uses two helper methods to find the elements in the visual tree:
<ListBox x:Name="lb">
<ListBox.ItemContainerStyle>
<Style TargetType="ListBoxItem">
<EventSetter Event="Selected" Handler="lbi_Selected"/>
</Style>
</ListBox.ItemContainerStyle>
<ListBox.ItemTemplate>
<DataTemplate>
<Expander x:Name="exp" Header="...">
<Expander.Style>
<Style TargetType="{x:Type Expander}">
<EventSetter Event="Expanded" Handler="exp_Expanded"/>
</Style>
</Expander.Style>
<TextBlock Text="{Binding}"/>
</Expander>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
List<Expander> expanders = new List<Expander>();
private void exp_Expanded(object sender, RoutedEventArgs e)
Expander expander = sender as Expander;
if (!expanders.Contains(expander))
expanders.Add(expander);
//select ListBoxItem
ListBoxItem lbi = FindParent<ListBoxItem>(expander);
lbi.IsSelected = true;
expanders.ForEach(exp => { if (exp != expander) exp.IsExpanded = false; });
void lbi_Selected(object sender, RoutedEventArgs e)
//expand expander:
Expander expander = FindChild<Expander>(sender as DependencyObject);
expander.IsExpanded = true;
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);
private T FindChild<T>(DependencyObject depencencyObject) where T : DependencyObject
if (depencencyObject != null)
for (int i = 0; i < VisualTreeHelper.GetChildrenCount(depencencyObject); ++i)
DependencyObject child = VisualTreeHelper.GetChild(depencencyObject, i);
T result = (child as T) ?? FindChild<T>(child);
if (result != null)
return result;
return null;
You should generally not try to implement some kind of logic or behaviour in the XAML markup, that's not what it is for. You may define your bindings in the XAML markup but when you want to customize things you should implement the behaviour programmatically.
Hope that helps.
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