Question

There has to be a better way then the following for getting “childItem”

    TaskItem task = (sender as Canvas).DataContext as TaskItem;
    TaskItem child = Tasks.CreateTask("New task", task);
    TreeViewItem item = treeView.ItemContainerGenerator.ContainerFromItem(task) as TreeViewItem;            

    item.UpdateLayout();
    TreeViewItem childItem = null;
    foreach (var i in item.GetDescendantContainers())
    {
        if (i.GetItem() == child)
            childItem = i;
    }

For some reason item.ItemGenerator.ContainerFromItem(child) does not work (must be due to the item having just been created)

Answer 1

Item container generation is asynchronous, so you cannot assume the container will exist as soon as the item was added. You will need to attach a handler to the ItemContainerGenerator.StatusChanged event so your code will be informed when container generation is complete.

Dr. WPF’s blog entry “ItemsControl: ‘G’ is for Generator” has a good description of the problem and provides an example of using StatusChanged:

private void AddScooby()
{
    _scooby = new Character("Scooby Doo");
    Characters.Add(_scooby);
    CharacterListBox.ItemContainerGenerator.StatusChanged
        += OnStatusChanged;
}

private void OnStatusChanged(object sender, EventArgs e)
{
    if (CharacterListBox.ItemContainerGenerator.Status
        == GeneratorStatus.ContainersGenerated)
    {
        CharacterListBox.ItemContainerGenerator.StatusChanged
            -= OnStatusChanged;
        ListBoxItem lbi = CharacterListBox.ItemContainerGenerator
            .ContainerFromItem(_scooby) as ListBoxItem;
        if (lbi != null)
        {
            lbi.IsSelected = true;
        }
    }
}