DotSpatial 自定义MapFunction_mapMain中绘制线（未添加到图层中）

using DotSpatial.Controls;
using DotSpatial.Symbology;
using GeoAPI.Geometries;
using System;
using System.Collections.Generic;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace DotSpatial20Test.LzqOP
{
    public class Lzq_FunctionClipPolygon : MapFunction
    {
        #region 定义变量

        private List<Coordinate> _coordinates;//折线段的集合
        private System.Drawing.Point _mousePosition;//鼠标位置
        private List<List<Coordinate>> _previousParts;//这次绘制前折线段点集合
        private bool _standBy;//判断是否注销当前工具       

        #endregion
        /// <summary>
        /// 构造函数
        /// </summary>
        /// <param name="map"></param>
        public Lzq_FunctionClipPolygon(IMap map) : base(map)
        {
            _previousParts = new List<List<Coordinate>>();//初始化
            _coordinates = new List<Coordinate>();
            YieldStyle = YieldStyles.LeftButton | YieldStyles.RightButton;

            if (map != null)
            {
                (map as Control).MouseLeave += MapMouseLeave;
            }
            Name = "绘制线";
        }
        /// <summary>
        /// 鼠标离开控制区域
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void MapMouseLeave(object sender, EventArgs e)
        {
            Map.Invalidate();
        }

        /// <summary>
        /// 激活Function
        /// </summary>
        protected override void OnActivate()
        {
            if(!_standBy) //非注销状态
            {
                _previousParts = new List<List<Coordinate>>();
                _coordinates = new List<Coordinate>();
            }
            _standBy = false;
            base.OnActivate();
        }
        /// <summary>
        /// 注销
        /// </summary>
        protected override void OnDeactivate()
        {
            if(_standBy)
            {
                return;
            }
            _standBy = true;
            Map.Invalidate();
            //base.OnDeactivate();
        }
        /// <summary>
        /// 鼠标移动
        /// </summary>
        /// <param name="e"></param>
        protected override void OnMouseMove(GeoMouseArgs e)
        {
            //注销后，跳过
            if(_standBy)
            {
                return;
            }

            //无坐标时,跳过
            if(_coordinates==null||_coordinates.Count==0)
            {
                return;
            }

            //鼠标位置点
            Coordinate c1 = e.GeographicLocation;

            //当点数大于0时
            if(_coordinates.Count>0)
            {
                //将地理坐标转换为屏幕坐标
                List<Point> points = _coordinates.Select(coord => Map.ProjToPixel(coord)).ToList();
                //获取鼠标上一个位置和最后一个点的矩形区域
                Rectangle oldRect = SymbologyGlobal.GetRectangle(_mousePosition, points[points.Count - 1]);
                //获取鼠标和左后一个点矩形区域
                Rectangle newRect = SymbologyGlobal.GetRectangle(e.Location, points[points.Count - 1]);
                //合并区域
                Rectangle invalidRect = Rectangle.Union(newRect, oldRect);
                //刷新区域
                invalidRect.Inflate(220, 20);
                Map.Invalidate(invalidRect);
            }
            //设置鼠标位置
            _mousePosition = e.Location;

            base.OnMouseMove(e);
        }

        /// <summary>
        /// 鼠标弹起
        /// </summary>
        /// <param name="e"></param>
        protected override void OnMouseUp(GeoMouseArgs e)
        {
            //注销，跳过
            if (_standBy)
            {
                return;
            }

            //右键结束此次操作，开始下次操作
            if(e.Button ==MouseButtons.Right)
            {
                _coordinates = new List<Coordinate>();//坐标点集清空
                //Map.Invalidate();
                //base.OnDeactivate();
            }
            else
            {
                _coordinates.Add(e.GeographicLocation);//将当前鼠标点添加至坐标点集中
                Map.Invalidate();
            }

            base.OnMouseUp(e);
        }
        /// <summary>
        /// 绘制地图
        /// </summary>
        /// <param name="e"></param>
        protected override void OnDraw(MapDrawArgs e)
        {
            //当前鼠标在屏幕坐标系下的坐标
            Point mouseTest = Map.PointToClient(Control.MousePosition);
            //鼠标是否在地图内
            bool hasMouseInMapCtrl = Map.ClientRectangle.Contains(mouseTest);

            #region 定义绘图工具 画笔等

            //画笔——红色
            Pen penRed = new Pen(Color.Red, 2F);
            //画笔——蓝色
            Pen penBlue = new Pen(Color.Blue, 2F);
            //画刷——红色
            Brush brushRed = new SolidBrush(Color.Red);
            //画刷——蓝色
            Brush brushBlue = new SolidBrush(Color.FromArgb(60, 0, 0, 255));
            //字体
            Font drawFont = new Font("Arial", 12);
            //抗锯齿
            e.Graphics.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.AntiAlias;

            #endregion

            //点序列
            List<Point> points = new List<Point>();

            //绘制当前点集
            if(_coordinates!=null)
            {
                //获取此次绘制的所有点
                foreach(Coordinate coord in _coordinates)
                {
                    points.Add(Map.ProjToPixel(coord));//地理坐标转屏幕坐标
                }

                //点集数量>1
                if(points.Count>1)
                {
                    //绘制折线、节点
                    for(int i=0;i<points.Count-1;i++)
                    {
                        Point cp = points[i];
                        Point np = points[i + 1];
                        e.Graphics.DrawLine(penBlue, cp, np);
                        e.Graphics.FillRectangle(brushRed, new Rectangle(cp.X - 2, cp.Y - 2, 4, 4));
                    }
                }

                //点击数量>0时，绘制鼠标移动所构成的那条线
                if (points.Count > 0 && _standBy == false && hasMouseInMapCtrl)
                {
                    e.Graphics.DrawLine(penRed, points[points.Count - 1], _mousePosition);
                }
            }
            //释放变量
            penBlue.Dispose();
            penRed.Dispose();
            brushRed.Dispose();
            brushBlue.Dispose();
            drawFont.Dispose();
            base.OnDraw(e);
        }
    }
}

调用方法：

mapMain.Cursor = Cursors.Cross;
            var lzqFunctionClipPolygon = new Lzq_FunctionClipPolygon(mapMain);
            mapMain.ActivateMapFunction(lzqFunctionClipPolygon);

原文地址：https://www.cnblogs.com/kogame/p/12330628.html