将焦点设置在作为ListBoxItem内容的UserControl上的TextBox

private void ListBoxItem_Click(object sender, RoutedEventArgs e)
{
    ListBoxItem clickedItem = sender as ListBoxItem;
    if (clickedItem != null)
    {
        UserControl itemContent = clickedItem.Content as UserControl;
        if (itemContent != null)
        {
            TextBox textBox = FindVisualChild<TextBox>(itemContent);
            if (textBox != null)
            {
                textBox.Focus();
            }
        }
    }
}

private T FindVisualChild<T>(DependencyObject parent) where T : DependencyObject
{
    for (int i = 0; i < VisualTreeHelper.GetChildrenCount(parent); i++)
    {
        DependencyObject child = VisualTreeHelper.GetChild(parent, i);
        if (child != null && child is T)
        {
            return (T)child;
        }
        else
        {
            T childItem = FindVisualChild<T>(child);
            if (childItem != null)
                return childItem;
        }
    }
    return null;
}