MeasureOverride ArrangeOverride

		protected override Size MeasureOverride(Size constraint)
		{
			if (constraint.Width == double.PositiveInfinity || constraint.Height == double.PositiveInfinity)
				return Size.Empty;

			UpdateScrollInfo(constraint);

			foreach (UIElement child in InternalChildren)
			{
				child.Measure(ChildSize);
			}

			return constraint;
		}

		protected override Size ArrangeOverride(Size finalSize)
		{
			UpdateScrollInfo(finalSize);
			for (int i = 0; i < InternalChildren.Count; i++)
			{
				InternalChildren[i].Arrange(new Rect(new Point(i*ChildSize.Width, 0), ChildSize));
			}
			return finalSize;
		}

层层传递的作用，本自定义容器类定义这两个函数提供给它的上层容器调用，上层容器负责给下层的内容分配空间大小，以此来确定整个界面的布局。