通过LINQ和窗口来选择块参照，并且获取块的说明

/// <summary>

/// 获取窗口中块说明

/// </summary>

/// <param name="db">数据库对象</param>

/// <param name="pt1">窗口选择角点1</param>

/// <param name="pt2">窗口选择角点2</param>

/// <returns></returns>

public static void getBlocks(this Database db,Point3d pt1,Point3d pt2)

{

BlockTableRecord btr = new BlockTableRecord();

Editor ed = Autodesk.AutoCAD.ApplicationServices.Application.DocumentManager.GetDocument(db).Editor;

using (Transaction trans = db.TransactionManager.StartTransaction())

{

//选取模型空间中指定窗口中的块

var blocks = from d in db.SelectCrossingWindow<BlockReference>(pt1,pt2)

select d;

foreach (var bref in blocks)

{

btr =(BlockTableRecord) trans.GetObject(bref.BlockTableRecord, OpenMode.ForRead);

ed.WriteMessage("\n块名为："+ bref.Name + "\n块说明为：" + btr.Comments);

}

trans.Commit();

}

}

/// <summary>

/// 选择窗口中及和窗口四条边界相交的实体，实体类型为T

/// </summary>

/// <typeparam name="T">实体的类型</typeparam>

/// <param name="db">数据库对象</param>

/// <param name="pt1">窗口的一个角点</param>

/// <param name="pt2">窗口的另一个角点</param>

/// <returns>返回类型为T的实体</returns>

public static List<T> SelectCrossingWindow<T>(this Database db, Point3d pt1, Point3d pt2) where T : Entity

{

return SelectCrossingWindow<T>(db, pt1, pt2, OpenMode.ForRead, false);

}

/// <summary>

/// 选择窗口中及和窗口四条边界相交的实体，实体类型为T

/// </summary>

/// <typeparam name="T">实体的类型</typeparam>

/// <param name="db">数据库对象</param>

/// <param name="pt1">窗口的一个角</param>

/// <param name="pt2">窗口的另一个角点</param>

/// <param name="mode">实体的打开方式</param>

/// <param name="openErased">是否打开已删除的实体</param>

/// <returns>返回类型为T的实体</returns>

public static List<T> SelectCrossingWindow<T>(this Database db, Point3d pt1, Point3d pt2, OpenMode mode, bool openErased) where T : Entity

{

var trans = db.TransactionManager;

string dxfname = RXClass.GetClass(typeof(T)).DxfName;

List<T> ents = new List<T>();

Editor ed = Application.DocumentManager.MdiActiveDocument.Editor;

TypedValue[] values = { new TypedValue((int)DxfCode.Start, dxfname) };

var filter = new SelectionFilter(values);

var entSelected = ed.SelectCrossingWindow(pt1, pt2, filter);

if (entSelected.Status == PromptStatus.OK)

{

foreach (var id in entSelected.Value.GetObjectIds())

{

T t = (T)(object)trans.GetObject(id, mode, openErased);

ents.Add(t);

}

}

return ents;

}