TransactionManager.StartTransaction() throws NullReferenceException

[adam.krug]

Inside of DB.Object_Modified event handler I'm examining the modified object. Sometimes I need to retrieve another object based on an ObjectId, thus I use transaction. 90% of times it works but sometimes TransactionManager.StartTransaction() method throws a NullReferenceExeption internally (stack trace below). Any idea how could I prevent this from happening (is there any property of DBObject, Document or anything else I could use to check if I can safely start a transaction?

System.NullReferenceException: Object reference not set to an instance of an object.
at Autodesk.AutoCAD.Runtime.Interop.CheckNull(IntPtr returnValue)
at Autodesk.AutoCAD.ApplicationServices.TransactionManager.StartTransaction()

Eventually I could use a try-catch block but I'm looking for a more efficient way.

[Virupaksha_aithal]

Hi,

see if "StartOpenCloseTransaction" transaction helps in your case. refer https://adndevblog.typepad.com/autocad/2012/08/the-right-tools-for-the-job-autocad-part-5.html

[adam.krug]

Hi @Virupaksha_aithal ,

In my case it didn't help but still thanks for pointing out on the StartOpenCloseTransaction , very interesting read!

I'm not sure what exactly is causing the problem, seems like the context for starting the transaction is sometimes not valid. Anyways, I decided to change my original approach: during Db_ObjectModified event handler I only add the modified objects on a list and examine them only after a command is finished, using Doc_CommandEnded event handler. Then I also clean the list. Works.

[timgrote]

I've run into issues where there is no active document, and the code still runs from a palette or other event.

Checking for a null document has helped with that.

Document doc = CAD_App.DocumentManager.MdiActiveDocument;
if (doc == null) return;

[adam.krug]

Hi @timgrote 

In my case the ActiveDoc is not null, I'm getting the null reference exception inside of the StartTransaction() call.

If ActiveDoc was null, I wouldn't be able to even reach StartTransaction() 

[Alfred.NESWADBA]

Hi,

does your active doc have a valid database? Otherwise it could be the AutoCAD start window.

- alfred -

[_gile]

Hi,

The NullReferenceException is probably related to an instance of TransactionManager or the instance of Database (or Document) the TransactionManager is got from.

Try simply doing:

using (var tr = new OpenCloseTransaction())
{
    // do your stuff with tr here
}

[quan_hm]

hi @adam.krug , 

Can you make more clear about your approach (or a sample code) about using Doc_CommandEnded event handler. I want to use that to modify object properties after a command finish.