c# - 如何设置常量属性AttributeReference？

Question

是否可以更改 AttributeReference 的 Constant 属性？（属性 IsConstant 是只读的）

Answer 1

我不知道 objectarx，但在 .Net 中（因为你说 c#），试试这个：

        Database currentDB = Application.DocumentManager.MdiActiveDocument.Database;
        using (Transaction transaction = currentDB.TransactionManager.StartTransaction())
        {
            BlockTable blockTable = (BlockTable)transaction.GetObject(currentDB.BlockTableId, OpenMode.ForRead);

            //Create the block if it doesn't exist
            if (!blockTable.Has("MyBlock"))
            {
                using (BlockTableRecord myBlock = new BlockTableRecord())
                {
                    myBlock.Name = "MyBlock";
                    myBlock.Origin = Point3d.Origin;

                    //You can add geometry here, but I'm just going to create the attribute
                    using (AttributeDefinition attribute = new AttributeDefinition())
                    {
                        attribute.Position = Point3d.Origin;
                        attribute.Tag = "Constant";
                        attribute.Prompt = "Enter value: ";
                        attribute.TextString = "My value";
                        attribute.Height = 0.5;
                        attribute.Justify = AttachmentPoint.BottomLeft;
                        attribute.Constant = true;

                        myBlock.AppendEntity(attribute);

                        //add to the block table
                        blockTable.UpgradeOpen();
                        blockTable.Add(myBlock);
                        transaction.AddNewlyCreatedDBObject(myBlock, true);

                    }

                }

                transaction.Commit();
            }
        }

编辑： 我刚刚意识到你也说 AttributeReference 而不是 AttributeDefinition。在没有确定验证的情况下，我认为引用不能直接修改，因为该值是恒定的。因此，您必须在 BlockTableRecord 中更新块的定义，一旦获得它，基本过程相同。

这是更新的代码：

       Database currentDB = Application.DocumentManager.MdiActiveDocument.Database;
        using (Transaction transaction = currentDB.TransactionManager.StartTransaction())
        {
            BlockTable blockTable = (BlockTable)transaction.GetObject(currentDB.BlockTableId, OpenMode.ForRead);


            //Create the block if it doesn't exist
            if (blockTable.Has("MyBlock"))
            {
                //Get the block
                ObjectId myBlockID = blockTable["MyBlock"];
                BlockTableRecord myBlock = (BlockTableRecord)transaction.GetObject(myBlockID, OpenMode.ForRead);

                //iterate through objects and update the attribute definition
                if (myBlock.HasAttributeDefinitions)
                {
                    foreach (ObjectId oid in myBlock)
                    {
                        DBObject dbObject = transaction.GetObject(oid, OpenMode.ForRead);
                        if (dbObject is AttributeDefinition)
                        {
                            AttributeDefinition attribute = (AttributeDefinition)dbObject;

                            attribute.UpgradeOpen();

                            attribute.TextString = "NewValue";
                            attribute.Constant = true;
                        }
                    }
                }

                //Remember... BlockRerefences are glorified pointers to the BlockTableRecord that defines them
                //so let's get all block references associated to it and update them

                foreach (ObjectId oid in myBlock.GetBlockReferenceIds(false, true))
                {
                    BlockReference blockReference = (BlockReference)transaction.GetObject(oid, OpenMode.ForWrite);
                    blockReference.RecordGraphicsModified(true);
                }

                transaction.Commit();
            }
        }

Answer 2

您需要更改AttributeDefinition块表记录（属性Constant）中的 ，而不是AttributeReference. 此属性与所有AttributeReference.

从文档：

AutoCAD 本身从不创建常量 AttributeReference 对象。AutoCAD 根据引用的 BlockTableRecord 中的 AttributeDefinition 对象为每个 BlockReference 创建 AttributeReference 对象。如果遇到常量 AttributeDefinition，则 AutoCAD 使用 AttributeDefinition 本身，而不是创建匹配的 AttributeReference。