Collapse opened expanders in `Datatemplate`, when we open new one

Question

My view works like this. I have an Observable Collection, which contains objects put on the list. By clicking on any item, I can open an expander related to that item. Here is the question: How can I collapse (close) the previously opened expander when I open another one? I don't want to have a situation where multiple expanders are opened at the same time.

My WPF code looks like this:

 <Grid x:Name="ContentPanel" Grid.Row="1" Margin="12,0,12,0">
        <controls:Pivot>
            <controls:PivotItem>
                <ListBox x:Name="PizzaList" SelectionChanged="PizzaList_SelectionChanged" IsSynchronizedWithCurrentItem="false" >
                    <ListBox.ItemTemplate>
                        <DataTemplate x:Name="template">

                            <toolkit:ExpanderView Header="{Binding Name}" x:Name="expander" Style="{StaticResource ExpanderViewStyle}">
                                <toolkit:ExpanderView.Items>
                                   <!--first stack panel would contain all elements which would be showed 
                                    after clicking on listbox item-->
                                    <StackPanel Margin="20,0,0,0" Orientation="Vertical">
                  <!-- here is content of expander-->                    
                                    </StackPanel>
                                </toolkit:ExpanderView.Items>
                                <toolkit:ExpanderView.Expander>
                                    <TextBlock Text="{Binding Name_of_ingredients}" Width="500"></TextBlock>
                                </toolkit:ExpanderView.Expander>
                            </toolkit:ExpanderView>


                        </DataTemplate>
                    </ListBox.ItemTemplate>
                </ListBox>
            </controls:PivotItem>
        </controls:Pivot>
    </Grid>

I could have a static number of expanders if I were working with a fixed dataset, but when the expander is in a data template, the number of items could change. I'm not sure how to solve this.

Answer 1

I think this can help:

private void PizzaListSelectionChanged(object sender, SelectionChangedEventArgs e)
{
    foreach (var item in PizzaList.Items)
    {
        var listBoxItem =
            PizzaList.ItemContainerGenerator.ContainerFromItem(item) as ListBoxItem;
        var itemExpander = (Expander) GetExpander(listBoxItem);
        if (itemExpander != null)
            itemExpander.IsExpanded = false;
    }
}

and search of Expander

private static DependencyObject GetExpander(DependencyObject container)
{
    if (container is Expander) return container;

    for (var i = 0; i < VisualTreeHelper.GetChildrenCount(container); i++)
    {
        var child = VisualTreeHelper.GetChild(container, i);

        var result = GetExpander(child);
        if (result != null)
        {
            return result;
        }
    }

    return null;
}

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