HierarchicalDataTemplate TreeView-ContainerFromItem仅返回第一个Item的TreeViewItem

Question

I have a TreeView as follows:

<TreeView
    Loaded="tv_Loaded_1"
    DockPanel.Dock="Bottom"
    Name="tv"
    ItemsSource="{Binding XPath=*}">
    <TreeView.ItemTemplate>
        <HierarchicalDataTemplate
            ItemsSource="{Binding XPath=*}">
            <StackPanel
                Orientation="Horizontal">
                <TextBlock
                    Text="{Binding Name}"></TextBlock>
            </StackPanel>
        </HierarchicalDataTemplate>
    </TreeView.ItemTemplate>
</TreeView>

In code behind, I am using the following xml as DataContext:

XmlDocument doc = new XmlDocument();
doc.LoadXml(@"<a><b><c></c><d></d></b><e><f></f><g></g></e></a>");
DataContext = doc;

TreeView is generating fine, but while enumerating the Items, I get TreeViewItem only for the first XmlNode(root node ie <a> ) and the remaining XmlNodes down in the hierarchy do not have any corresponding TreeViewItems present.

private IEnumerable<TreeViewItem> Enumerate(ItemCollection items)
{
    foreach (XmlElement element in items)
    {
        TreeViewItem item = tv.ItemContainerGenerator.ContainerFromItem(element) as TreeViewItem;
        if (item != null) //When second call with <a>.Items, item is null
        {
            yield return item;
        }
        //Enumerate is called again with <a>.Items 
        //Exception in second call, because item is null
        foreach (TreeViewItem i in Enumerate(item.Items))
        {
            yield return i;
        }
    }
}

private void tv_Loaded_1(object sender, RoutedEventArgs e)
{
   var list = Enumerate(tv.Items).ToList();
}

Why the rest of the XmlNodes in the Tree do not have any TreeViewItem present?

Any help is greatly appreciated.

Answer 1

It's because the other items aren't in tv, they are in the 'a' TreeViewItem. But, they really are not in 'a' yet either because the TreeViewItem isn't expanded and the layout hasn't been updated.

You can make it work by passing in the ItemsControl (either tv or the parent TreeViewItem) and using it to get the ContainerFromItem. But, you will have to expand the item and update it's layout before you will get a container.

Here is some code to do the above. A side effect will be that the tree is fully expanded.

private IEnumerable<TreeViewItem> Enumerate(ItemsControl itemsControl, ItemCollection items)
{
    foreach (XmlElement element in items)
    {
        TreeViewItem item = itemsControl.ItemContainerGenerator.ContainerFromItem(element) as TreeViewItem;
        if (item != null) //When second call with <a>.Items, item is null
        {
            item.IsExpanded = true;
            item.UpdateLayout();

            yield return item;
        }
        //Enumerate is called again with <a>.Items 
        //Exception in second call, because item is null
        foreach (TreeViewItem i in Enumerate(item, item.Items))
        {
            yield return i;
        }
    }
}

private void tv_Loaded_1(object sender, RoutedEventArgs e)
{
    var list = Enumerate(tv, tv.Items).ToList();
}

Actually, you only really need to pass in the ItemsControl. Also, I put some code in to close the tree back up.

private IEnumerable<TreeViewItem> Enumerate(ItemsControl itemsControl)
{
    foreach (XmlElement element in itemsControl.Items)
    {
        TreeViewItem item = itemsControl.ItemContainerGenerator.ContainerFromItem(element) as TreeViewItem;
        if (item != null) //When second call with <a>.Items, item is null
        {
            item.IsExpanded = true;
            item.UpdateLayout();

            yield return item;
        }
        //Enumerate is called again with <a>.Items 
        //Exception in second call, because item is null
        foreach (TreeViewItem i in Enumerate(item))
        {
            yield return i;
        }
    }
}

private void tv_Loaded_1(object sender, RoutedEventArgs e)
{
    var list = Enumerate(tv).ToList();
    // Unexpand all the items
    list.ForEach(tvi => tvi.IsExpanded = false);
}