ObservableCollection and ListBoxItem DataTemplate generation problem

Question

Something strange is going on with ObservableCollection.

I have the following code:

private readonly ObservableCollection _displa         


        

Answer 1

The wpf layout engine won't have been through the layout and arrange pass so your listboxitems won't have been given a size yet. Sticking in the message box will allow the background threads that do this run. Try forcing a call to Measure() on your items before looking at their size.

Answer 2

SOLVED

This creates somewhat flickering effect for a fraction of second (as if loading items one by one), but actually suits my needs.

The point is to refresh the UI for an item before retrieving its height.

I have created an extension method:

    public static void RefreshUI(this DependencyObject obj)
    {
        obj.Dispatcher.Invoke(System.Windows.Threading.DispatcherPriority.Loaded, (Action)delegate { });
    }

And then before retrieving the height, I refresh the UI.

private double CalculateItemsHeight(int index)
    {
        ListBoxItem lbi = _box.ItemContainerGenerator.ContainerFromIndex(index) as ListBoxItem;
        if (lbi != null) {
            lbi.RefreshUI();
            return lbi.ActualHeight;
        }
        return 0;
    }

Answer 3

Actually, I was trying to get this to work and I found the ".UpdateLayout()" function, which works perfectly for me. I realize that you're doing vertical and I'm doing horizontal, but here's my code, it's pretty simple:

for (int i = 0; i < listOfItems.ItemsIn.Count; ++i)
    {
        //CalculateItemsHeight(i);

        ListBoxItem abc = (lb.ItemContainerGenerator.ContainerFromItem(lb.Items[i]) as ListBoxItem);
        abc.UpdateLayout();
        totalWidth += abc.ActualWidth;
    }

Hopefully this helps!