topic Transaction Null Reference and eWasOpenforWrite Error in .NET Forum

Transaction Null Reference and eWasOpenforWrite Error

drobertsY4GL3 — Mon, 23 Nov 2020 22:14:34 GMT

I cannot seem to find a solution to getting the blockreference when inside an AttributeModifiedEventHandler. When using StartTransaction() I get a NullReferenceException and when using StartOpenCloseTransaction() I get a 'eWasOpenforWrite' error.

Please see below for further info and the event handler code.

Double clicking a dynamic block and selecting "OK" inside the enhanced attribute editor gives a NullReferenceException at:

using (Transaction transaction1 = transactionManager.StartTransaction())

Copying the dynamic block works however as expected.

If I change: StartTransaction() to:

using (var transaction1 = transactionManager.StartOpenCloseTransaction())

The attribute editor then works, but copying the block gives an 'eWasOpenForWrite' error at:

var blockReference = transaction1.GetObject(id, OpenMode.ForRead) as BlockReference;

Below is the full EventHandler.

private void AttributeModifiedEventHandler(object sender, Autodesk.AutoCAD.DatabaseServices.ObjectEventArgs args) { var transactionManager = currentDatabase.TransactionManager; AttributeReference attributeRef; string CadHandle = ""; bool updateDB = false; if (args.DBObject is AttributeReference) { attributeRef = (AttributeReference)args.DBObject; using (Transaction transaction1 = transactionManager.StartTransaction()) { var blockTable = transaction1.GetObject(currentDatabase.BlockTableId, OpenMode.ForRead) as BlockTable; var blockTableRecord = transaction1.GetObject(blockTable[BlockTableRecord.ModelSpace], OpenMode.ForRead) as BlockTableRecord; foreach (ObjectId id in blockTableRecord) { // check if the current ObjectId is a block reference one if (id.ObjectClass.DxfName == "INSERT") { var blockReference = transaction1.GetObject(id, OpenMode.ForRead) as BlockReference; if (blockReference.Id == attributeRef.OwnerId) { CadHandle = blockReference.Handle.ToString(); } }; } transaction1.Commit(); } } }

Any help anyone can give is extremely appreciated!

Thank you.

Re: Transaction Null Reference and eWasOpenforWrite Error

norman.yuan — Tue, 24 Nov 2020 13:20:19 GMT

It looks to me that the purpose of the code in your AttributeModifiedEventHandler() does is to find the handle of attribute owner (blockreference) and assign it to a variable "CadHandle" (it also looks to me that the code in the eventhandler is not "full" - the local variable "CadHandle" is not used after being assigned value)

I do not understand is why you need to loop through entire ModelSpace for that while the agrs.DBObject has already had all information you need?

You can simply:

private void XXXXXXXHandler(object sender, ObjectEventArgs args)

{

var att = args.DBObject As AttributeReference;

if (att != null)

{

var CadHandle=att.OwnerId.Handle.ToString();

// do something with CadHandle...

// but do not attempt to modify anything in this event handler, in general

}

Re: Transaction Null Reference and eWasOpenforWrite Error

drobertsY4GL3 — Tue, 24 Nov 2020 15:24:19 GMT

Thank you Mr. Yuan.

This is my first AutoCAD plugin, so I am very grateful for the help. Your solution is a good clean example of how it should be done.