自定义Marker，可以理解为在地图上自定义图标（Custom Marker），先看看GMap的地图和图标的显示方式：

Map控件上可以添加Overlay（图层），可以添加多个图层，先添加的图层在下面显示。

图层上可以添加GMapMarker，当然也可以添加GMapPolygon和GMapRoute，后续介绍。

在地图的使用中常要求的功能就是添加自定义图标，可以点击图标、删除图标、拖动图标、高亮图标等。

下面介绍这些功能的实现（主要是基于WinForm的，WPF的可以参考官方Demo实现）：

1、自定义图标，使用官方的Marker：

复制代码 代码如下:
Bitmap bitmap = Bitmap.FromFile("F:\\Projects\\GMapDemo\\GMapDemo\\Image\\A.png") as Bitmap;
GMapMarker marker = new GMarkerGoogle(point, bitmap);

直接使用GMap.NET.WindowsForms.Markers中的GMarkerGoogle，传入一个Bitmap，就可以使用自定义的图片来做图标。

2、继承GMapMarker，自定义Marker：

复制代码 代码如下:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using GMap.NET;
using GMap.NET.WindowsForms;
using System.Drawing;

namespace GMapWinFormDemo
{
    class GMapMarkerImage : GMapMarker
    {
        private Image image;
        public Image Image
        {
            get
            {
                return image;
            }
            set
            {
                image = value;
                if (image != null)
                {
                    this.Size = new Size(image.Width, image.Height);
                }
            }
        }

        public Pen Pen
        {
            get;
            set;
        }

        public Pen OutPen
        {
            get;
            set;
        }

        public GMapMarkerImage(GMap.NET.PointLatLng p, Image image)
            : base(p)
        {
            Size = new System.Drawing.Size(image.Width, image.Height);
            Offset = new System.Drawing.Point(-Size.Width / 2, -Size.Height / 2);
            this.image = image;
            Pen = null;
            OutPen = null;
        }

        public override void OnRender(Graphics g)
        {
            if (image == null)
                return;

            Rectangle rect = new Rectangle(LocalPosition.X, LocalPosition.Y, Size.Width, Size.Height);
            g.DrawImage(image, rect);

            if (Pen != null)
            {
                g.DrawRectangle(Pen, rect);
            }

            if (OutPen != null)
            {
                g.DrawEllipse(OutPen, rect);
            }
        }

        public override void Dispose()
        {
            if (Pen != null)
            {
                Pen.Dispose();
                Pen = null;
            }

            if (OutPen != null)
            {
                OutPen.Dispose();
                OutPen = null;
            }

            base.Dispose();
        }
    }
}

介绍下GMapMarkerImage三个属性的作用：

Image：保存图标的图片。

Pen：在图片外围画DrawRectangle的Pen，当其不为null的时候，会在图片的外围画一个矩形，实现高亮（highlight）的效果。

OutPen：在图片外围画DrawEllipse的Pen，当其不为null的时候，会在图片外围画一个一个椭圆，设置这个值可以实现闪动。

3、移动图标（Move Marker）的实现：

在MapControl中添加如下事件的响应：

复制代码 代码如下:
mapControl.MouseDown += new MouseEventHandler(mapControl_MouseDown);
mapControl.MouseUp += new MouseEventHandler(mapControl_MouseUp);
mapControl.MouseMove += new MouseEventHandler(mapControl_MouseMove);

mapControl.OnMarkerClick += new MarkerClick(mapControl_OnMarkerClick);
mapControl.OnMarkerEnter += new MarkerEnter(mapControl_OnMarkerEnter);
mapControl.OnMarkerLeave += new MarkerLeave(mapControl_OnMarkerLeave);

MouseDown和MouseUp中判断左键是否按下（用左键来移动图标）。

OnMarkerEnter中设置选中的Marker，同时设置Pen的值，实现高亮。

OnMarkerLeave中取消选中的Marker，取消Pen的值，取消高亮。

MouseMove中更新选中选中Marker的Position就可以了。

4、图标闪动的实现：

需要一个定时器：使用的是Form下的Timer，定时器响应的事件：

复制代码 代码如下:
void blinkTimer_Tick(object sender, EventArgs e)
        {
            foreach (GMapMarker m in objects.Markers)
            {
                if (m is GMapMarkerImage)
                {
                    GMapMarkerImage marker = m as GMapMarkerImage;
                    if (marker.OutPen == null)
                        marker.OutPen = new Pen(Brushes.Red, 2);
                    else
                    {
                        marker.OutPen.Dispose();
                        marker.OutPen = null;
                    }
                }
            }
            mapControl.Refresh();
        }

更新所有Marker的OutPen的值（当然你也可以只更新某个Marker），通过在图标上画圈圈来实现闪动，当然你也可以通过设置Marker的IsVisible属性来实现自己想要的效果。。。

效果图如下：

全部代码如下：

复制代码 代码如下:
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using GMap.NET;
using GMap.NET.WindowsForms;
using GMap.NET.MapProviders;
using GMap.NET.WindowsForms.Markers;

namespace GMapWinFormDemo
{
    public partial class MainForm : Form
    {
        private GMapOverlay objects = new GMapOverlay("objects"); //放置marker的图层
        private GMapMarkerImage currentMarker;
        private bool isLeftButtonDown = false;

        private Timer blinkTimer = new Timer();

        public MainForm()
        {
            InitializeComponent();

            try
            {
                System.Net.IPHostEntry e = System.Net.Dns.GetHostEntry("www.google.com.hk");
            }
            catch
            {
                mapControl.Manager.Mode = AccessMode.CacheOnly;
                MessageBox.Show("No internet connection avaible, going to CacheOnly mode.", "GMap.NET Demo", MessageBoxButtons.OK, MessageBoxIcon.Warning);
            }

            mapControl.CacheLocation = Environment.CurrentDirectory + "\\GMapCache\\"; //缓存位置
            mapControl.MapProvider = GMapProviders.GoogleChinaMap; //google china 地图
            mapControl.MinZoom = 2;  //最小比例
            mapControl.MaxZoom = 17; //最大比例
            mapControl.Zoom = 5;     //当前比例
            mapControl.ShowCenter = false; //不显示中心十字点
            mapControl.DragButton = System.Windows.Forms.MouseButtons.Left; //左键拖拽地图
            mapControl.Position = new PointLatLng(32.064,118.704); //地图中心位置：南京

            mapControl.OnMapZoomChanged += new MapZoomChanged(mapControl_OnMapZoomChanged);
            mapControl.MouseClick += new MouseEventHandler(mapControl_MouseClick);
            mapControl.MouseDown += new MouseEventHandler(mapControl_MouseDown);
            mapControl.MouseUp += new MouseEventHandler(mapControl_MouseUp);
            mapControl.MouseMove += new MouseEventHandler(mapControl_MouseMove);

            mapControl.OnMarkerClick += new MarkerClick(mapControl_OnMarkerClick);
            mapControl.OnMarkerEnter += new MarkerEnter(mapControl_OnMarkerEnter);
            mapControl.OnMarkerLeave += new MarkerLeave(mapControl_OnMarkerLeave);

            mapControl.Overlays.Add(objects);
        }

        void mapControl_MouseMove(object sender, MouseEventArgs e)
        {
            if (e.Button == System.Windows.Forms.MouseButtons.Left && isLeftButtonDown)
            {
                if (currentMarker != null)
                {
                    PointLatLng point = mapControl.FromLocalToLatLng(e.X, e.Y);
                    currentMarker.Position = point;
                    currentMarker.ToolTipText = string.Format("{0},{1}", point.Lat, point.Lng);
                }
            }
        }

        void mapControl_MouseUp(object sender, MouseEventArgs e)
        {
            if (e.Button == System.Windows.Forms.MouseButtons.Left)
            {
                isLeftButtonDown = false;
            }
        }

        void mapControl_MouseDown(object sender, MouseEventArgs e)
        {
            if (e.Button == System.Windows.Forms.MouseButtons.Left)
            {
                isLeftButtonDown = true;
            }
        }

        void mapControl_OnMarkerLeave(GMapMarker item)
        {
            if (item is GMapMarkerImage)
            {
                currentMarker = null;
                GMapMarkerImage m = item as GMapMarkerImage;
                m.Pen.Dispose();
                m.Pen = null;
            }
        }

        void mapControl_OnMarkerEnter(GMapMarker item)
        {
            if (item is GMapMarkerImage)
            {
                currentMarker = item as GMapMarkerImage;
                currentMarker.Pen = new Pen(Brushes.Red, 2);
            }
        }

        void mapControl_OnMarkerClick(GMapMarker item, MouseEventArgs e)
        {
        }

        void mapControl_MouseClick(object sender, MouseEventArgs e)
        {
            if(e.Button == System.Windows.Forms.MouseButtons.Right)
            {
                //objects.Markers.Clear();
                PointLatLng point = mapControl.FromLocalToLatLng(e.X,e.Y);
                //GMapMarker marker = new GMarkerGoogle(point, GMarkerGoogleType.green);
                Bitmap bitmap = Bitmap.FromFile("F:\\Projects\\GMapDemo\\GMapDemo\\Image\\A.png") as Bitmap;
                //GMapMarker marker = new GMarkerGoogle(point, bitmap);
                GMapMarker marker = new GMapMarkerImage(point, bitmap);
                marker.ToolTipMode = MarkerTooltipMode.OnMouseOver;
                marker.ToolTipText = string.Format("{0},{1}", point.Lat, point.Lng);
                objects.Markers.Add(marker);
            }
        }

        void mapControl_OnMapZoomChanged()
        {
        }

        private void buttonBeginBlink_Click(object sender, EventArgs e)
        {
            blinkTimer.Interval = 1000;
            blinkTimer.Tick += new EventHandler(blinkTimer_Tick);
            blinkTimer.Start();
        }

        void blinkTimer_Tick(object sender, EventArgs e)
        {
            foreach (GMapMarker m in objects.Markers)
            {
                if (m is GMapMarkerImage)
                {
                    GMapMarkerImage marker = m as GMapMarkerImage;
                    if (marker.OutPen == null)
                        marker.OutPen = new Pen(Brushes.Red, 2);
                    else
                    {
                        marker.OutPen.Dispose();
                        marker.OutPen = null;
                    }
                }
            }
            mapControl.Refresh();
        }

        private void buttonStopBlink_Click(object sender, EventArgs e)
        {
            blinkTimer.Stop();
            foreach (GMapMarker m in objects.Markers)
            {
                if (m is GMapMarkerImage)
                {
                    GMapMarkerImage marker = m as GMapMarkerImage;
                    marker.OutPen.Dispose();
                    marker.OutPen = null;
                }
            }
            mapControl.Refresh();
        }
    }
}