How does ItemContainerGenerator.ContainerFromItem work with a grouped list?

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You have to listen and react to the ItemsGenerator.StatusChanged Event and wait until the ItemContainers are generated before you can access them with ContainerFromElement.

Searching further, I’ve found a thread in the MSDN forum from someone who has the same problem. This seems to be a bug in WPF, when one has a GroupStyle set. The solution is to punt the access of the ItemGenerator after the rendering process. Below is the code for your question. I tried this, and it works:

    void ItemContainerGenerator_StatusChanged(object sender, EventArgs e)
    {
        if (listBox1.ItemContainerGenerator.Status
            == System.Windows.Controls.Primitives.GeneratorStatus.ContainersGenerated)
        {
            listBox1.ItemContainerGenerator.StatusChanged
                -= ItemContainerGenerator_StatusChanged;
            Dispatcher.BeginInvoke(System.Windows.Threading.DispatcherPriority.Input,
                new Action(DelayedAction));
        }
    }

    void DelayedAction()
    {
        var i = listBox1.ItemContainerGenerator.ContainerFromIndex(1) as ListBoxItem;

        // select and keyboard-focus the second item
        i.IsSelected = true;
        i.Focus();
    }

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