用C#开发CAD2016插件 将拾取的多段线向左缓冲1米构建region对象，如果有其它多段线与regio对象有重叠，则裁剪掉

开发CAD2016插件需要使用AutoCAD的API，具体步骤如下：

1. 创建新的C#类库项目，添加对`AcMgd.dll`和`AcDbMgd.dll`的引用。

2. 在类库中创建一个类，实现`IAcadCommand`接口，这个类将成为AutoCAD命令。

3. 在类中实现`Execute()`方法，用于处理命令逻辑。首先获取当前文档和编辑器对象：

   Document doc = Application.DocumentManager.MdiActiveDocument;
   Editor ed = doc.Editor;

4. 使用`PromptEntityOptions`和`PromptEntityResult`类获取用户选择的多段线对象：

   PromptEntityOptions opt = new PromptEntityOptions("\n请选择一条多段线：");
   opt.SetRejectMessage("\n只能选择多段线！");
   opt.AddAllowedClass(typeof(Polyline), true);

   PromptEntityResult res = ed.GetEntity(opt);
   if (res.Status != PromptStatus.OK) return;
   
   Polyline pline = null;
   using (Transaction tr = doc.TransactionManager.StartTransaction())
   {
       pline = tr.GetObject(res.ObjectId, OpenMode.ForRead) as Polyline;
       tr.Commit();
   }

5. 构建区域对象：

   Region region = null;
   using (Transaction tr = doc.TransactionManager.StartTransaction())
   {
       DBObjectCollection objs = new DBObjectCollection();
       Curve curve = null;
       for (int i = 0; i < pline.NumberOfVertices - 1; i++)
       {
           Point3d startPt = pline.GetPoint3dAt(i);
           Point3d endPt = pline.GetPoint3dAt(i + 1);
           Line line = new Line(startPt, endPt);
           curve = line.GetOffsetCurves(1)[0] as Curve;
           objs.Add(curve);
       }

       region = Region.CreateFromCurves(objs);
       tr.Commit();
   }

6. 获取所有与区域对象相交的多段线，进行裁剪：

   using (Transaction tr = doc.TransactionManager.StartTransaction())
   {
       BlockTable bt = tr.GetObject(doc.Database.BlockTableId, OpenMode.ForRead) as BlockTable;
       BlockTableRecord btr = tr.GetObject(bt[BlockTableRecord.ModelSpace], OpenMode.ForWrite) as BlockTableRecord;

       foreach (ObjectId id in btr)
       {
           Entity ent = tr.GetObject(id, OpenMode.ForRead) as Entity;
           if (ent != null && ent.GetType() == typeof(Polyline))
           {
               Polyline poly = ent as Polyline;
               if (poly.ObjectId != pline.ObjectId && region.IntersectWith(poly, Intersect.OnBothOperands, new Plane())[0] != null)
               {
                   DBObjectCollection objs = new DBObjectCollection();
                   Curve curve = null;
                   for (int i = 0; i < poly.NumberOfVertices - 1; i++)
                   {
                       Point3d startPt = poly.GetPoint3dAt(i);
                       Point3d endPt = poly.GetPoint3dAt(i + 1);
                       Line line = new Line(startPt, endPt);
                       curve = line.GetOffsetCurves(1)[0] as Curve;
                       objs.Add(curve);
                   }

                   Region interRegion = Region.CreateFromCurves(objs);
                   if (region.Area > interRegion.Area)
                   {
                       region.BooleanOperation(BooleanOperationType.BoolIntersect, interRegion);
                   }
               }
           }
       }

       btr.AppendEntity(region);
       tr.AddNewlyCreatedDBObject(region, true);
       tr.Commit();
   }

最后将类库编译生成dll文件，将其加载到AutoCAD中并输入命令名称即可使用。