#1,192 – Calling Arrange on Child Elements

When you author a custom control that contains child elements, you should call the Arrange method of each child object within your ArrangeOverride method.

Below is an example, from a custom element with one child.  The parent control has a dependency property, ChildProperty, representing the single child element.

        protected override Size ArrangeOverride(Size finalSize)
        {
            UIElement childElement = (UIElement)GetValue(ChildProperty);
            if (childElement != null)
                childElement.Arrange(new Rect(new Point(0.0, 0.0), finalSize));

            return finalSize;
        }

Below is a second example, from a custom panel that renders a treemap-like element.  The ChildrenTreemapOrder method returns an enumerable of ChildAndRect objects.

protected override Size ArrangeOverride(Size finalSize)
{
    foreach (ChildAndRect child in ChildrenTreemapOrder(InternalChildren.Cast<UIElement>(), finalSize))
        child.Element.Arrange(child.Rectangle);

    return finalSize;
}