Windows Phone 7: Iterate over ListBoxItems in a list box to focus on a control

I am developing a small Windows Phone 7 application and I ran into a wall. I am updating items within a ListBox and I need to set focus on a control after the update. It turns out that it is not a trivial task -- I need to iterate over the entire list box to get to the control and then set focus on it.

Here is the XAML of my list box:

I was using the VisualTreeHelper class to iterate over the ListBox, but I was not getting to the ListBoxItems. I was getting ListBox, ScrollViewer, Border, Grid, ContentPresenter, ItemsPresenter, VirtualizingStackPanel, and other controls, but no ListBoxItems. After reading this, the problem was fixed by calling the

UpdateLayout

method. The rest was simple. Here is my code.

void SetFocusOnTextBox(DependencyObject element, int primaryKey)
        {
            for (int i = 0; i < VisualTreeHelper.GetChildrenCount(element); i++)
            {
                if (foundItem == false) //global flag that stops processing once the control is found
                {
                    DependencyObject child = VisualTreeHelper.GetChild(element, i);
                    StackPanel s = child as StackPanel;
                    if (s != null)
                        FindAllChildrenOfAStackPanel(child, primaryKey);
                    if (foundItem == false)
                        SetFocusOnTextBox(child, primaryKey);
                    else
                        break;
                }
            }
            foundItem = false;
        }

        void FindAllChildrenOfAStackPanel(DependencyObject element, int primaryKey)
        {
            StackPanel s = element as StackPanel;
            if (s != null)
            {
                for (int i = 0; i < VisualTreeHelper.GetChildrenCount(element); i++)
                {
                    TextBox t = VisualTreeHelper.GetChild(element, i) as TextBox;
                    if (t != null)
                        if (t.Name == primaryKey)
                        {
                            t.Focus();
                            foundItem = true;
                            break;
                        }
                }
            }
        }