C# AutoCAD2010 dwg选择块，再在该块位置上选择外部块将其替换，其他位置上的同名块不变，完整代码

以下是一个示例代码，可以实现选择指定块并替换它的功能：

using Autodesk.AutoCAD.ApplicationServices;
using Autodesk.AutoCAD.DatabaseServices;
using Autodesk.AutoCAD.EditorInput;
using Autodesk.AutoCAD.Geometry;
using Autodesk.AutoCAD.Runtime;

namespace ReplaceBlock
{
    public class Commands
    {
        [CommandMethod("RB")]
        public void ReplaceBlock()
        {
            // 获取当前文档和编辑器
            Document doc = Application.DocumentManager.MdiActiveDocument;
            Editor ed = doc.Editor;

            // 选择要替换的块
            PromptEntityOptions peo = new PromptEntityOptions("\n选择要替换的块: ");
            peo.SetRejectMessage("\n请选择块！");
            peo.AddAllowedClass(typeof(BlockReference), true);
            PromptEntityResult per = ed.GetEntity(peo);
            if (per.Status != PromptStatus.OK) return;
            ObjectId blockId = per.ObjectId;

            // 获取要替换成的块
            PromptEntityOptions peo2 = new PromptEntityOptions("\n选择要替换成的块: ");
            peo2.SetRejectMessage("\n请选择块！");
            peo2.AddAllowedClass(typeof(BlockReference), true);
            PromptEntityResult per2 = ed.GetEntity(peo2);
            if (per2.Status != PromptStatus.OK) return;
            ObjectId newBlockId = per2.ObjectId;

            // 获取要替换的块的位置
            Transaction tr = doc.TransactionManager.StartTransaction();
            using (tr)
            {
                BlockReference oldBlock = (BlockReference)tr.GetObject(blockId, OpenMode.ForWrite);
                Point3d position = oldBlock.Position;

                // 获取该位置上的块
                BlockTable bt = (BlockTable)tr.GetObject(doc.Database.BlockTableId, OpenMode.ForRead);
                BlockTableRecord model = (BlockTableRecord)tr.GetObject(bt[BlockTableRecord.ModelSpace], OpenMode.ForRead);
                foreach (ObjectId id in model)
                {
                    Entity entity = (Entity)tr.GetObject(id, OpenMode.ForRead);
                    if (entity is BlockReference)
                    {
                        BlockReference block = (BlockReference)entity;
                        if ((block.Name == oldBlock.Name) && (block.Position == position))
                        {
                            // 替换块
                            block.UpgradeOpen();
                            block.BlockTableRecord = newBlockId;
                            block.DowngradeOpen();
                        }
                    }
                }

                tr.Commit();
            }
        }
    }
}

此代码假设要替换的块和要替换成的块已经存在于 AutoCAD 文档中，且它们具有相同的名称。它首先使用 `PromptEntityOptions` 对话框让用户选择要替换的块和要替换成的块。然后，它获取要替换的块的位置，并在该位置上查找同名的块。最后，它将找到的块的 `BlockTableRecord` 属性设置为要替换成的块的 `ObjectId`。