Redefine a Block (.NET)

Use any of the Block object methods and properties to redefine a block. When you redefine a block, all the references to that block in the drawing are immediately updated to reflect the new definition.

Redefinition affects previous and future insertions of a block. Constant attributes are lost and replaced by any new constant attributes. Variable attributes remain unchanged, even if the new block has no attributes.

Redefine the objects in a block definition

This example creates a block and adds a circle to the definition of the block. The block is then inserted into the drawing as a block reference. The circle in the block definition is updated, and the block reference is updated automatically.

C# Example

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

[CommandMethod("RedefiningABlock")]
public void RedefiningABlock()
{
    // Get the current database and start a transaction
    Database acCurDb;
    acCurDb = Application.DocumentManager.MdiActiveDocument.Database;

    using (Transaction acTrans = acCurDb.TransactionManager.StartTransaction())
    {
        // Open the Block table for read
        BlockTable acBlkTbl;
        acBlkTbl = acTrans.GetObject(acCurDb.BlockTableId, OpenMode.ForRead) as BlockTable;

        if (!acBlkTbl.Has("CircleBlock"))
        {
            using (BlockTableRecord acBlkTblRec = new BlockTableRecord())
            {
                acBlkTblRec.Name = "CircleBlock";

                // Set the insertion point for the block
                acBlkTblRec.Origin = new Point3d(0, 0, 0);

                // Add a circle to the block
                using (Circle acCirc = new Circle())
                {
                    acCirc.Center = new Point3d(0, 0, 0);
                    acCirc.Radius = 2;

                    acBlkTblRec.AppendEntity(acCirc);

                    acTrans.GetObject(acCurDb.BlockTableId, OpenMode.ForWrite);
                    acBlkTbl.Add(acBlkTblRec);
                    acTrans.AddNewlyCreatedDBObject(acBlkTblRec, true);

                    // Insert the block into the current space
                    using (BlockReference acBlkRef = new BlockReference(new Point3d(0, 0, 0), acBlkTblRec.Id))
                    {
                        BlockTableRecord acModelSpace;
                        acModelSpace = acTrans.GetObject(acCurDb.CurrentSpaceId, OpenMode.ForWrite) as BlockTableRecord;

                        acModelSpace.AppendEntity(acBlkRef);
                        acTrans.AddNewlyCreatedDBObject(acBlkRef, true);

                        Application.ShowAlertDialog("CircleBlock has been created.");
                    }
                }
            }
        }
        else
        {
            // Redefine the block if it exists
            BlockTableRecord acBlkTblRec =
                acTrans.GetObject(acBlkTbl["CircleBlock"], OpenMode.ForWrite) as BlockTableRecord;

            // Step through each object in the block table record
            foreach (ObjectId objID in acBlkTblRec)
            {
                DBObject dbObj = acTrans.GetObject(objID, OpenMode.ForRead) as DBObject;

                // Revise the circle in the block
                if (dbObj is Circle)
                {
                    Circle acCirc = dbObj as Circle;

                    acTrans.GetObject(objID, OpenMode.ForWrite);
                    acCirc.Radius = acCirc.Radius * 2;
                }
            }

            // Update existing block references
            foreach (ObjectId objID in acBlkTblRec.GetBlockReferenceIds(false, true))
            {
                BlockReference acBlkRef = acTrans.GetObject(objID, OpenMode.ForWrite) as BlockReference;
                acBlkRef.RecordGraphicsModified(true);
            }

            Application.ShowAlertDialog("CircleBlock has been revised.");
        }

        // Save the new object to the database
        acTrans.Commit();

        // Dispose of the transaction
    }
}