ArcMobile的CoordinateCollection在逆时针添加点时自动调整节点顺序的问题

　　为了使用ArcMobile实现量测功能，LZ自定义了一个MapGraphicLayer用于绘图，代码如下：

using System.Drawing;
using ESRI.ArcGIS.Mobile;
using ESRI.ArcGIS.Mobile.Geometries;

namespace LandInspections
{
    public class MeasureLayer : MapGraphicLayer
    {
        /// Defines a symbol class instance for displaying point
        private Symbol drawSymbol;

        /// Defines a CoordinateCollection instance to store custom features
        private CoordinateCollection coordinateCollection = new CoordinateCollection();

        /// Get or set coordinate collection stored in custom graphic layer
        public CoordinateCollection Coordinates
        {
            get
            {
                return coordinateCollection;
            }
            set
            {
                coordinateCollection = value;
            }
        }

        /// Initializes a new instance of custom graphic layer
        public MeasureLayer()
            : base("MeasureLayer")
        {
            drawSymbol = new Symbol(
                new PointPaintOperation(
                    Color.Green, 3, 0, Color.LightGreen, 100, 25, PointPaintStyle.Circle));
        }

        /// Draw method being called after adding to map
        protected override void Draw(Display display)
        {
            //return if display is null
            if (display == null)
                return;
            //return if drawing is cancelled
            if (display.DrawingCanceled)
                return;
            drawSymbol.DrawArea(display, coordinateCollection);
        }

        protected override void Dispose(bool disposing)
        {
            //Dispose symbol implementing IDisposible
            try
            {
                if (disposing)
                {
                    if (drawSymbol != null)
                        drawSymbol.Dispose();
                    drawSymbol = null;

                    coordinateCollection = null;
                }
            }
            finally
            {
                base.Dispose(disposing);
            }
        }
    }
}

　　在“量测”按钮所在的窗体代码中，添加如下代码：

/// <summary>
/// MapGraphicLayer的坐标点
/// </summary>
private CoordinateCollection coords = new CoordinateCollection();

private BtnMeasure_Click(object sender, EventArgs e)
{
    if (this.txtMeasure.Visible)//txtMeasure是用来显示量测结果的控件
    {
        this.txtMeasure.Visible = false;
        this.coords.Clear();
        this.map1.MapGraphicLayers.Remove(this.measureLayer);
        this._mapAction = MyMapAction.None;
    }
    else
    {
        this.txtMeasure.Text = "量测：\r\n长度：0.000 米\r\n面积：0.000 平方米";
        this.measureLayer = new MeasureLayer();
        this.measureLayer.Coordinates = this.coords;
        this.map1.MapGraphicLayers.Add(this.measureLayer);
        this._mapAction == MyMapAction.Measure;
        this.txtMeasure.Visible = true;
    }
}

private void map1_MouseUp(object sender, MapMouseEventArgs e)
{
    if (this._mapAction == MyMapAction.Measure)
    {
        Coordinate coord = this.map1.ToMap(e.X, e.Y);
        this.coords.Add(coord);
        Polyline line = new Polyline(this.measureLayer.Coordinates);
        Polygon area = new Polygon(this.measureLayer.Coordinates);
        this.txtMeasure.Text = String.Format("量测：\r\n长度：{0} 米\r\n面积：{1} 平方米",
            line.GetLength().ToString("f3"), area.GetArea().ToString("f3"));
        this.map1.Refresh();
    }
}

　　运行后，发现顺时针点击屏幕的绘图结果正确，但是逆时针点击屏幕时绘图结果错误。

　　检查后发现是因为ESRI.ArcGIS.Mobile.Geometries.CoordinateCollection类的Add方法对点集的顺序进行了自动调整，在this.coords.Add(coord)时点集的顺序已经被改变了。

　　添加点1：CoordinateCollection中点集为[1]。

　　添加点2：CoordinateCollection中点集为[1,2,1]。

　　添加点3：CoordinateCollection中点集为[1,3,2,1]。

　　添加点4：CoordinateCollection中点击为[1,4,2,3,1]。

　　为解决这一问题，LZ在程序中定义一个List<Coordinate> coords，用来存储正确顺序的点集，在自定义的MapGraphicLayer中添加一个SetCoordinate方法，用来保证以顺时针方向添加节点到CoordinateCollection中。代码如下：

public void SetCoordinate(System.Collections.Generic.List<Coordinate> coords)
{
    if (coords == null || coords.Count < 1)
        return;
    if (this.coordinateCollection == null)
        this.coordinateCollection = new CoordinateCollection();
　　this.coordinateCollection.Clear();
    //若为顺时针，则直接赋值
    for (int i = 0; i < coords.Count; i++)
    {
        this.coordinateCollection.Add(new Coordinate(coords[i].X, coords[i].Y));
        if (this.coordinateCollection.IsCounterClockwise == true)
            break;
    }
    //若为逆时针，则反向以顺时针方式将点集添加到CoordinateCollection中
    if (this.coordinateCollection.IsCounterClockwise == true)
    {
        this.coordinateCollection.Clear();
        this.coordinateCollection.Add(new Coordinate(coords[0].X, coords[0].Y));
        for (int i = coords.Count - 1; i > 0; i--)
        {
            this.coordinateCollection.Add(new Coordinate(coords[i].X, coords[i].Y));
        }
    }
}

　　相应的，“量测”功能所在窗体的代码也需要进行相应的修改，代码如下：

/// <summary>
/// MapGraphicLayer的坐标点
/// </summary>
private List<Coordinate> coords = new List<Coordinate>();

private BtnMeasure_Click(object sender, EventArgs e)
{
    if (this.txtMeasure.Visible)//txtMeasure是用来显示量测结果的控件
    {
        this.txtMeasure.Visible = false;
        this.coords.Clear();
        this.map1.MapGraphicLayers.Remove(this.measureLayer);
        this._mapAction = MyMapAction.None;
    }
    else
    {
        this.txtMeasure.Text = "量测：\r\n长度：0.000 米\r\n面积：0.000 平方米";
        this.measureLayer = new MeasureLayer();
        this.measureLayer.Coordinates.Clear();
        this.map1.MapGraphicLayers.Add(this.measureLayer);
        this._mapAction == MyMapAction.Measure;
        this.txtMeasure.Visible = true;
    }
}

private void map1_MouseUp(object sender, MapMouseEventArgs e)
{
    if (this._mapAction == MyMapAction.Measure)
    {
        Coordinate coord = this.map1.ToMap(e.X, e.Y);
        this.coords.Add(coord);
        this.measureLayer.SetCoordinate(this.coords);
        Polyline line = new Polyline(this.measureLayer.Coordinates);
        Polygon area = new Polygon(this.measureLayer.Coordinates);
        this.txtMeasure.Text = String.Format("量测：\r\n长度：{0} 米\r\n面积：{1} 平方米",
            line.GetLength().ToString("f3"), area.GetArea().ToString("f3"));
        this.map1.Refresh();
    }
}

　　经过测试，这种方式是可行的。之后大概是因为无聊，也可能是为了验证自己的想法，又分别测试了完全反向插入节点和完全正向插入节点的情况，结果出乎意料，竟然都是正确的？？？

　　完全反向插入节点：即将[1,2,3,4]以[1,4,3,2]的顺序插入，无论节点顺序是顺时针还是逆时针。测试代码如下：

public void SetCoordinate(System.Collections.Generic.List<Coordinate> coords)
{
   if (coords == null || coords.Count < 1)
       return;
   if (this.coordinateCollection == null)
       this.coordinateCollection = new CoordinateCollection();
   this.coordinateCollection.Clear();
   //反向插入节点
this.coordinateCollection.Add(new Coordinate(coords[0].X, coords[0].Y));
   for (int i = coords.Count - 1; i > 0; i--)
   {
       this.coordinateCollection.Add(new Coordinate(coords[i].X, coords[i].Y));
   }
}

　　完全正向插入节点：即将[1,2,3,4]以[1,2,3,4]的顺序插入，无论节点顺序是顺时针还是逆时针。测试代码如下：

public void SetCoordinate(System.Collections.Generic.List<Coordinate> coords)
{
    if (coords == null || coords.Count < 1)
        return;
    if (this.coordinateCollection == null)
        this.coordinateCollection = new CoordinateCollection();
    this.coordinateCollection.Clear();
    for (int i = 0; i < coords.Count; i++)
    {
        this.coordinateCollection.Add(new Coordinate(coords[i].X, coords[i].Y));
    }
}

　　最后的事实证明，只要每次绘图时，将所有的节点重新添加一次即可，于是LZ最终选择了完全正向插入节点的方式。