Is there a way to iterate in a ListBox Items templates?

Question

I have a list box that contains items that are represented by a single textbox.

When the user clicks a button, I want to iterate thru all these text boxes and check if their binding expressions are clean of errors; Should be something like:

    Dim errCount = 0
    For Each item In MyListBox.ListBoxItems 'There is no such thing ListBoxItems which is actually what I am looking for.
        Dim tb As TextBox = item '.........Dig in item to extract the textbox from the visual tree.
        errCount += tb.GetBindingExpression(TextBox.TextProperty).HasError
    Next
    If errCount Then
        'Errors found!
    End If

Any discussion would be really appreciated. Thanks.

Answer 1

There may be an easier way to do this, but here is one option that will work:

1) Iterate through the list of items.

Because you are using items source, ListBox.Items will refer to the data items in the ItemsSource.

for (int i = 0; i < ListBox.Items.Count; i++)
{
    // do work as follows below...
}

2) Get the containers for these items.

DependencyObject obj = ListBox.ItemContainerGenerator.ContainerFromIndex(i);

3) Use VisualTreeHelper to search for a TextBox child of the container visual.

TextBox box = FindVisualChild<TextBox>(obj);

Use this function to search for a visual child of the correct type:

public static childItem FindVisualChild<childItem>(DependencyObject obj)
    where childItem : DependencyObject
{
    // Search immediate children
    for (int i = 0; i < VisualTreeHelper.GetChildrenCount(obj); i++)
    {
        DependencyObject child = VisualTreeHelper.GetChild(obj, i);

        if (child is childItem)
            return (childItem)child;

        else
        {
            childItem childOfChild = FindVisualChild<childItem>(child);

            if (childOfChild != null)
                return childOfChild;
        }
    }

    return null;
}

4) Finally, examine the binding on the TextBox.

All put together, something like this:

private bool ValidateList(ListBox lb)
{
    for (int i = 0; i < lb.Items.Count; i++)
    {
        DependencyObject obj = lb.ItemContainerGenerator.ContainerFromIndex(i);
        TextBox box = FindVisualChild<TextBox>(obj);
        if (!TestBinding(box))
            return false;
    }

    return true;
}