1. Measure Arrange这两个方法是UIElement的方法

    MeasureOverride ArrangeOverride这两个方法是FrameworkElement的方法，FrameworkElement是UIElement的子类

    MeasureOverride传入父容器分配的可用空间，返回该容器根据其子元素大小计算确定的在布局过程中所需的大小。

    ArrangeOverride传入父容易最终分配的控件大小，返回使用的实际大小

2. MeasureOverride 用于计算本身及其子控件的大小

    ArrangeOverride用于布局本身及其子控件的位置和大小

3. WPF布局系统大概分为两步：Measure和Arrange

    Measure方法自顶而下，递归调用各子控件的Measure方法，Measure方法会把该控件所需的大小控件存在desired size属性中，控件根据各子控件的desired size 属性确定自身空间大小，并返回自己的desired size 

   Arrange方法发生在Measure中，传入Measure方法计算到的大小，利用控件的位置设置分配子控件的位置

简单来说，这两个方法一个管大小，一个管布局，都需要调用子类的Measure和Arrage

 

public class DiagnolPanel:Panel    {        protected override Size MeasureOverride(Size availableSize)        {            var mySize = new Size();            foreach (UIElement child in this.InternalChildren)            {                child.Measure(availableSize);                mySize.Width += child.DesiredSize.Width;                mySize.Height += child.DesiredSize.Height;            }            return mySize;        }            protected override Size ArrangeOverride(Size finalSize)        {            var location = new Point();            int childNumber = 0;            int middleChild = GetTheMiddleChild(this.InternalChildren.Count);            foreach (UIElement child in this.InternalChildren)            {                               if (childNumber < middleChild)                {                    child.Arrange(new Rect(location, child.DesiredSize));                    location.X += child.DesiredSize.Width;                    location.Y += child.DesiredSize.Height;                }                else                {                    //The x location will always keep increasing, there is no need to take care of it                    location.X = GetXLocationAfterMiddleChild(childNumber);                    //If the UIElements are odd in number                    if (this.InternalChildren.Count % 2 != 0)                    {                         //We need to get the Y location of the child before middle location,                         //to have the same Y location for the child after middle child                                              int relativeChildBeforeMiddle = middleChild - (childNumber - middleChild);                        location.Y = GetYLocationAfterMiddleChild(relativeChildBeforeMiddle);                    }                    else                    {                       ///TODO: Do the design for the even number of children                    }                    child.Arrange(new Rect(location, child.DesiredSize));                }                childNumber++;            }            return finalSize;        }        private double GetXLocationAfterMiddleChild(int childNUmber)        {            double xLocation = 0;            for (int i = 0; i < childNUmber; i++)            {                xLocation += this.InternalChildren[i].DesiredSize.Width;            }            return xLocation;        }        private double GetYLocationAfterMiddleChild(int relativeChildNumber)        {                        UIElement correspondingChild = this.InternalChildren[relativeChildNumber - 2];            Point pointCoordinates =             correspondingChild.TransformToAncestor((Visual)this.Parent).Transform(new Point(0, 0));            return pointCoordinates.Y;        }        private int GetTheMiddleChild(int count)        {            int middleChild;            if (count % 2 == 0)            {                middleChild = count / 2;            }            else            {                middleChild = (count / 2) + 1;            }            return middleChild;        }    }}

 

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