public class CustomControl1 : Panel
    {
        /// <summary>
        /// 先測(cè)量需要多大尺寸，做個(gè)申報(bào)準(zhǔn)備
        /// </summary>
        /// <param name="constraint">限定的尺寸，比如，規(guī)定了width和height</param>
        /// <returns></returns>
        protected override Size MeasureOverride(Size constraint)
        {
            //定義預(yù)期的寬度和高度
            double height = 0, width = 0;
            UIElement element;
            //遍歷每個(gè)元素，計(jì)算所需的總尺寸
            for (int i = 0; i < Children.Count; i++)
            {
                element = Children[i];
                //按照限定的尺寸測(cè)量一下自己，拿鏡子找著自己
                element.Measure(constraint);
                if (height < element.DesiredSize.Height)
                    height = element.DesiredSize.Height;
                width += element.DesiredSize.Width;
            }
            //申報(bào)，我需要這個(gè)尺寸
            return new Size(width, height);
        }
       
        /// <summary>
        /// 排列每個(gè)元素
        /// </summary>
        /// <param name="arrangeBounds">測(cè)量的尺寸</param>
        /// <returns></returns>
        protected override Size ArrangeOverride(Size arrangeBounds)
        {
            double currentX = 100;
            UIElement element;
            for (int i = 0; i < Children.Count; i++)
            {
                element = Children[i];
                //排列每個(gè)元素
                Children[i].Arrange(new Rect(currentX, 0, element.DesiredSize.Width, element.DesiredSize.Height));
                currentX += element.DesiredSize.Width;
            }
            return arrangeBounds;
        }
    }

 <local:CustomControl1  Width="300" Background="Gray" HorizontalAlignment="Right" Margin="0,20,151,280">
            <Rectangle Width="100" Height="50" Fill="Red" Margin="10,10,0,0" />
            <Rectangle Width="100" Height="50" Fill="Yellow" Margin="10,10,0,0" />
            <Rectangle Width="100" Height="50" Fill="Green" Margin="10,10,0,0" />
        </local:CustomControl1>