在Engine的工具(ITool)裡:

OnClick事件處理函式中:

首先需要獲取一個圖層,作為Snapping的參照,

IFeatureLayer targetLayer

然後宣告一個IMovePointFeedBack作為滑鼠移動時捕捉點的顯示:

1. IMovePointFeedback m_pMovePtFeed = new MovePointFeedback();  
2. mFeedback = (IDisplayFeedback)m_pMovePtFeed;  
3. ISimpleMarkerSymbol simpleMarkerSymbol = new SimpleMarkerSymbolClass();  
4. IRgbColor pRGBColor = new RgbColorClass();  
5. pRGBColor.Red = 0;  
6. pRGBColor.Green = 0;  
7. pRGBColor.Blue = 0;  
8. simpleMarkerSymbol.Color = pRGBColor;  
9. simpleMarkerSymbol.Size = 3;  
10. simpleMarkerSymbol.Style = ESRI.ArcGIS.Display.esriSimpleMarkerStyle.esriSMSSquare;  
11. ISymbol symbol = simpleMarkerSymbol as
     ISymbol;  
12. symbol.ROP2 = esriRasterOpCode.esriROPNotXOrPen;  
13. //symbol.ROP2 = esriRasterOpCode.;
14. m_pMovePtFeed.Symbol = (ISymbol)simpleMarkerSymbol;  

然後開始Feedback的顯示(tmpPoint是指開始的點,其實影響不大,如果不想要源點在螢幕上的話,可以取一個在螢幕外的點):

1. m_pMovePtFeed.Display = mMapControl.ActiveView.ScreenDisplay;  
2. m_pMovePtFeed.Start(tmpPoint, tmpPoint);  

在OnMouseMove事件中:

1. IPoint pPoint2 = null;  
2. IPoint pPoint = pMap.ActiveView.ScreenDisplay.DisplayTransformation.ToMapPoint(x, y);  
3. pPoint2 = Snapping(pPoint.X, pPoint.Y, targetLayer, pMap, 10);  
4. if (pPoint2 == null)  
5. pPoint2 = pPoint;  
6. ((IMovePointFeedback)mFeedback).MoveTo(pPoint2);  

其中Snapping函式即為最主要的查詢函式,其功能為根據輸入的點座標在目標圖層上查詢最為相近的點(也即需要捕捉的點),返回該點,若沒有找到則返回NULL,最後一個引數的含義是,在地圖控制元件上,以多少個畫素為單位在周邊查詢捕捉點.

1. public IPoint Snapping(double x, double y, IFeatureLayer iFeatureLyr, IMapControl3 axMapControl1,double snappingDis)  
2.         {  
3.             IPoint iHitPoint = null;  
4.             IMap iMap = axMapControl1.Map;  
5.             IActiveView iView = axMapControl1.ActiveView;  
6.             IFeatureClass iFClss = iFeatureLyr.FeatureClass;  
7.             IPoint point = new PointClass();  
8.             point.PutCoords(x, y);  
9.             double length = ConvertPixelsToMapUnits(axMapControl1.ActiveView, snappingDis);  
10.             ITopologicalOperator pTopo = point as ITopologicalOperator;  
11.             IGeometry pGeometry = pTopo.Buffer(length).Envelope as IGeometry;  
12.             ISpatialFilter spatialFilter = new SpatialFilterClass();  
13.             spatialFilter.GeometryField = iFeatureLyr.FeatureClass.ShapeFieldName;  
14.             spatialFilter.SpatialRel = esriSpatialRelEnum.esriSpatialRelIntersects;  
15.             spatialFilter.Geometry = pGeometry;  
16.             IFeatureCursor cursor = iFClss.Search(spatialFilter, false);  
17.             IFeature iF = cursor.NextFeature();  
18.             if (iF == null) returnnull;  
19.             IPoint iHitPt = new ESRI.ArcGIS.Geometry.Point();  
20.             IHitTest iHitTest = iF.Shape as IHitTest;  
21.             double hitDist = 0;  
22.             int partIndex = 0;  
23.             int vertexIndex = 0;  
24.             bool bVertexHit = false;  
25.             // Tolerance in pixels for line hits
26.             double tol = ConvertPixelsToMapUnits(iView, snappingDis);  
27.             if (iHitTest.HitTest(point, tol, esriGeometryHitPartType.esriGeometryPartBoundary,  
28.                 iHitPt, ref hitDist, ref partIndex, ref vertexIndex, ref bVertexHit))  
29.             {  
30.                 iHitPoint = iHitPt;  
31.             }  
32.             //axMapControl1.ActiveView.Refresh();
33.             return iHitPoint;  
34.         }  
35.         publicdouble ConvertPixelsToMapUnits(IActiveView pActiveView, double pixelUnits)  
36.         {  
37.             double realWorldDisplayExtent;  
38.             int pixelExtent;  
39.             double sizeOfOnePixel;  
40.             pixelExtent = pActiveView.ScreenDisplay.DisplayTransformation.get_DeviceFrame().right - pActiveView.ScreenDisplay.DisplayTransformation.get_DeviceFrame().left;  
41.             realWorldDisplayExtent = pActiveView.ScreenDisplay.DisplayTransformation.VisibleBounds.Width;  
42.             sizeOfOnePixel = realWorldDisplayExtent / pixelExtent;  
43.             return pixelUnits * sizeOfOnePixel;  
44.         }  

此時即可實現滑鼠實時地捕捉目標圖層上的物件,若需要獲取當前位置的捕捉點時,則可以在相應事件(例如OnMouseDown或OnDbClick)中呼叫:

1. IPoint pPoint = ((IMovePointFeedback)mFeedback).Stop();  

這時實時捕捉將會停止,若需要重新開始捕捉,則在之後呼叫這些語句即可:

1. //重新開始Snap
2. IPoint tmpPoint = new PointClass();  
3. tmpPoint.PutCoords(pMap.Extent.XMin - 1, pMap.Extent.YMin - 1);  
4. IMovePointFeedback m_pMovePtFeed = (IMovePointFeedback)mFeedback;  
5. m_pMovePtFeed.Display = pMap.ActiveView.ScreenDisplay;  
6. m_pMovePtFeed.Start(tmpPoint, tmpPoint);