Question

How can I make a silverlight listbox have all items be the same size and have them take up 100% of the listbox height. I.e. 1 item would be the height of the listbox, 2 items would each be 50% of the height of the list box, etc…

Edit – Here is the code

public class UniformPanel : Panel
{
    protected override Size MeasureOverride(Size availableSize)
    {
        Size panelDesiredSize = new Size();

        for (int i = 0; i < Children.Count; i++)
        {
            UIElement child = Children[i];
            child.Measure(availableSize);
            var childDesiredSize = child.DesiredSize;
            panelDesiredSize.Height += childDesiredSize.Height;
            if (panelDesiredSize.Width < childDesiredSize.Width)
            {
                panelDesiredSize.Width = childDesiredSize.Width;
            }
        }

        return panelDesiredSize;
    }
    protected override Size ArrangeOverride(Size finalSize)
    {
        double height = finalSize.Height/Children.Count;
        for (int i = 0; i < Children.Count; i++)
        {
            UIElement child = Children[i];
            Size size = new Size(finalSize.Width, height);
            child.Arrange(new Rect(new Point(0, i * height), size));
        }
        return finalSize; // Returns the final Arranged size
    }
}

Answer 1

I see, your requirement is just to make each item get TotalHeight/itemsCount right.. In that case you can do the trick with UniformGrid(which is already there as part of the platform) by making Columns=1
Use the following XAML

        <ListBox VerticalContentAlignment="Stretch"  HorizontalContentAlignment="Stretch">
        <ListBox.ItemsPanel>
            <ItemsPanelTemplate>
                <UniformGrid IsItemsHost="True" Columns="1"/>
            </ItemsPanelTemplate>
        </ListBox.ItemsPanel>
          <Button />
          <Button />
          <Button />
    </ListBox>

UPDATE : silverlight doesnt have a UniformGrid, but you can get one I ported from WPF to Silverlight here