ArcEngine 10.2 捕捉使用

  最近看了下ArcEngine的捕捉，记录下，以备后用，如果转载，请注明出处。

  除了自己编码实现的捕捉效果，ArcEngine主要通过两个接口实现捕捉，即ISnappingEnvironment和IEngineSnapEnvironment，刚开始我看到这两个东东，一直以为是ArcEngine里面使用捕捉的两个接口，实际上根本不是这么回事，是捕捉的两种实现方式，网上大多是IEngineSnapEnvironment这个接口的用法，让我也走了不少弯路，下面来一一说明。

  IEngineSnapEnvironment是实现捕捉的旧接口，实际上是两个，IEngineSnapEnvironment和ISnapEnvironment，分别对应Engine和DeskTop，这些接口只能用于编辑会话中，捕捉效果比较简单粗暴，不够灵活，不推荐使用。

  ISnappingEnvironment是新的接口，网上查到是10.1出现的，可以在编辑、自定义工具中使用，能够设置捕捉过程中显示的字体、颜色、捕捉类型等等，效果比较好，推荐。

  使用过程（C#）：

  ISnappingEnvironment使用的过程必须用到IHookHelper2，Engine帮助里面有说明，不要问我为什么。

  ISnappingEnvironment 赋值：

  IExtensionMaIHookHelper2 hookHelper = new HookHelperClass
   {
          Hook = pMapControl
   } as IHookHelper2;

IExtensionManager extensionManager = hookHelper.ExtensionManager;
if (extensionManager != null)
{
    IExtension extension = extensionManager.FindExtension(new UIDClass
     {
           Value = "{E07B4C52-C894-4558-B8D4-D4050018D1DA}"//捕捉
     });
    IExtension extension = extensionManager.FindExtension(guid);

    ISnappingEnvironment pSnappingEnvironment = null;
    pSnappingEnvironment = extension as ISnappingEnvironment;

    pSnappingEnvironment.Enabled = true;//开启捕捉 JOJO
    pSnappingEnvironment.ShowSnapTips = true;//显示捕捉提示 JOJO

    pSnappingEnvironment.IgnoreIMSLayers = true; //忽略服务底图，如果为false，在捕捉缓冲中有时候可以捕捉到，但时间成本较高 JOJO

    pSnappingEnvironment.SnappingType = esriSnappingType.esriSnappingTypePoint; //只捕捉点 JOJO
    pSnappingEnvironment.SnapTipType = esriSnappingTipType.esriSnappingTipLayerName; //捕捉提示显示图层名 JOJO

    //设置字体、颜色看帮助吧，我是直接拷贝过来使用的

    pSnappingEnvironment.SnapTipSymbol = textSymbol;
}

  工具中使用（接口中）：

  ISnappingFeedback feedback;//展示捕捉，主要是靠这个 JOJO
  IPointSnapper pointsnapper; //可以获取捕捉修正的坐标 JOJO

   public override void OnClick()

  {

     //捕捉使用的变量赋值

    feedback = new SnappingFeedbackClass();
    feedback.Initialize(m_MapControl, pSnappingEnvironment, true);
    pointsnapper = pSnappingEnvironment.PointSnapper;

  }

   public override void OnMouseDown(int button, int shift, int x, int y)

  {

   //..........自己的业务逻辑代码

  //捕捉 JOJO

    IPoint pPt = m_activeView.ScreenDisplay.DisplayTransformation.ToMapPoint(x, y);//m_activeView是mapcontrol里面的activeView JOJO

    IPoint point = m_activeView.ScreenDisplay.DisplayTransformation.ToMapPoint(x, y);
    ISnappingResult snapResult = this.pointsnapper.Snap(point);
    this.feedback.Update(snapResult, 0);
    if (snapResult == null)
        return;

    pPt = snapResult.Location;

   //.......业务逻辑代码

  }    

  public override void OnMouseMove(int button, int shift, int x, int y)
  {
    IPoint pointcurrentcoords = m_activeView.ScreenDisplay.DisplayTransformation.ToMapPoint(x, y);
    ISnappingResult snapResult = this.pointsnapper.Snap(pointcurrentcoords);
    this.feedback.Update(snapResult, 0);           
  }

  以上，一个捕捉效果就可以实现了，最后记录一下捕捉的知识：

  捕捉类型（esriSnappingType）：

  

Constant	Value	Description
esriSnappingTypeNone	0	No snap.
esriSnappingTypePoint	1	Snap to point.
esriSnappingTypeEndpoint	2	Snap to endpoint.
esriSnappingTypeVertex	4	Snap to vertex.
esriSnappingTypeEdge	8	Snap to edge.
esriSnappingTypeMidpoint	16	Snap to midpoint.
esriSnappingTypeIntersection	32	Intersection snapping.
esriSnappingTypeTangent	64	Tangent snapping.

  捕捉是通过捕捉缓存来实现的，以下操作都会造成缓存刷新（不翻译了）：  

• A layer is added, moved, or deleted from the table of contents.
• The scale suppression of a layer is changed.
• The visibility of a layer is changed.
• A definition query on a layer is changed.
• A SQL query on a layer is changed.
• A layer’s data source is changed.
• A feature is created, updated, or deleted.
• The extent of the map changes.
• The active data frame changes.
• The active view changes (for example, the focus changes from the main map window to a viewer window or you switch from data view to layout view in ArcMap).
• The snapping tolerance (ISnappingEnvironment.Tolerance) is updated.
• Intersection snapping is turned on or off.
• Text snapping is enabled or disabled.
• CacheShapes, UpdateCachedShapes, or RemoveCachedShapes is called.
• The ISnappingEnvironment.IgnoreIMSLayers property is changed.

The snapping cache is cleared when any of the following events are fired:

• IHookHelperEvents.OnHookUpdated
• IActiveViewEvents.ContentsChanged
• IActiveViewEvents.FocusMapChanged
• IObjectClassEvents.OnChange
• IObjectClassEvents.OnCreate
• IObjectClassEvents.OnDelete