ArcGIS Engine中实现ArcMap的捕捉效果

注意要将捕捉相关接口的对象放在OnCreate方法中，这样在初始化就可以有捕捉效果，（捕捉对象赋值放在OnClick中出现第一次点击之前不能捕捉的BUG）

这里是直接在工具中实现的 ，可以按需求将捕捉效果的实现方式进行改写。

using System;
using System.Drawing;
using System.Runtime.InteropServices;
using ESRI.ArcGIS.ADF.BaseClasses;
using ESRI.ArcGIS.ADF.CATIDs;
using ESRI.ArcGIS.Controls;
using System.Windows.Forms;
using ESRI.ArcGIS.Geometry;
using ESRI.ArcGIS.Display;
using ESRI.ArcGIS.esriSystem;  

namespace DemoForm.Tools
{
     public sealed class SnapTool : BaseTool
    {
        private IHookHelper m_hookHelper = null;
        private IPoint m_snapPt;
        private ISnappingEnvironment m_SnapEnv;
        private IPointSnapper m_Snapper;
        private ISnappingFeedback m_SnapFeedback;
        private INewLineFeedback m_feedback;
        private ISnappingResult m_snapRst;  

        public SnapTool()
        {
            //
            // TODO: Define values for the public properties
            //
            base.m_category = ""; //localizable text
            base.m_caption = "";  //localizable text
            base.m_message = "This should work in ArcMap/MapControl/PageLayoutControl";  //localizable text
            base.m_toolTip = "";  //localizable text
            base.m_name = "";   //unique id, non-localizable (e.g. "MyCategory_MyTool")
            try
            {
                //
                // TODO: change resource name if necessary
                //
                string bitmapResourceName = GetType().Name + ".bmp";
                base.m_bitmap = new Bitmap(GetType(), bitmapResourceName);
                base.m_cursor = new System.Windows.Forms.Cursor(GetType(), GetType().Name + ".cur");
            }
            catch (Exception ex)
            {
                System.Diagnostics.Trace.WriteLine(ex.Message, "Invalid Bitmap");
            }
        }  

        #region Overridden Class Methods  

        public override void OnCreate(object hook)
        {
            try
            {
                m_hookHelper = new HookHelperClass();
                m_hookHelper.Hook = hook;
                if (m_hookHelper.ActiveView == null)
                {
                    m_hookHelper = null;
                }
            }
            catch
            {
                m_hookHelper = null;
            }  

            if (m_hookHelper == null)
                base.m_enabled = false;
            else
                base.m_enabled = true;  

            // TODO:  Add other initialization code
            UID uid = new UIDClass();
            uid.Value = "{E07B4C52-C894-4558-B804-D4050018D1DA}";
            IExtensionManager extMar = (m_hookHelper as IHookHelper2).ExtensionManager;
            IExtension ext = extMar.FindExtension(uid);
            m_SnapEnv = ext as ISnappingEnvironment;
            m_Snapper = m_SnapEnv.PointSnapper;
            m_SnapFeedback = new SnappingFeedbackClass();
            m_SnapFeedback.Initialize(m_hookHelper.Hook, m_SnapEnv, true); 

        }    

        public override void OnClick()
        {
            //
        }  

        public override void OnMouseDown(int Button, int Shift, int X, int Y)
        {
            IPoint ppt = m_hookHelper.ActiveView.ScreenDisplay.DisplayTransformation.ToMapPoint(X, Y);
            if (m_snapPt != null)
            {
                ppt = m_snapPt;
            }
            if (m_feedback != null)
            {
                m_feedback = new NewLineFeedbackClass();
                m_feedback.Display = m_hookHelper.ActiveView.ScreenDisplay;
                m_feedback.Start(ppt);
            }
            else
            {
                m_feedback.AddPoint(ppt);
            }
        }  

        public override void OnMouseMove(int Button, int Shift, int X, int Y)
        {
            IPoint ppt = m_hookHelper.ActiveView.ScreenDisplay.DisplayTransformation.ToMapPoint(X, Y);
            m_snapPt = ppt;
            m_snapRst = m_Snapper.Snap(m_snapPt);
            m_SnapFeedback.Update(m_snapRst, 0);
            if (m_snapRst != null)
            {
                m_snapPt = m_snapRst.Location;
            }
            if (m_feedback != null)
            {
                m_feedback.MoveTo(m_snapPt);
            }
        }  

        public override void OnMouseUp(int Button, int Shift, int X, int Y)
        {
            // TODO:  Add SnapTool.OnMouseUp implementation
        }
        #endregion
    }
}