Why is MdiActiveDocument null in the beginning in AutoCAD 2015+? - autocad

Question

I am working in AutoCAD 2014 using Visual Studio 2013.
With my code I access the MdiActiveDocument's database from the DocumentManager .
Using the database I start a transaction and use the GetObject method of the transaction to retrieve Entity objects.
Database acCurDb = Application.DocumentManager.MdiActiveDocument.Database;
using (Transaction acTrans = acCurDb.TransactionManager.StartTransaction())
{
var obj = acTrans.GetObject(id, OpenMode.ForRead);
if (obj is Entity)
{
// do stuff
}
acTrans.Commit();
}
This works fine while I am in development and start AutoCAD from inside of Visual Studio. In development I set the "Start external program" switch in the Debug tab of the application properties so it starts AutoCAD for me and everything works great.
The issue I am having is that in production when the app is loaded by AutoCAD via registry settings (I use demand loading) the MdiActiveDocument is null so the code crashes. I have discovered there is a document in the Application.DocumentManager but when I assign the database from that document to acCurDb the TransactionManager throws an error with I try to use the StartTransaction method.
if (Application.DocumentManager.Count > 0)
{
foreach(Document doc in Application.DocumentManager)
{
acCurDb = doc.Database;
break;
}
}
using (Transaction acTrans = acCurDb.TransactionManager.StartTransaction())
{
}
Can someone help me understand why the MdiActiveDocument is null and/or direct me to the proper way to get a Transaction object in AutoCAD?

Answer 1

Beginning in 2015, AutoCAD may have a null active document on startup depending on user system variables. It's just another check you have to add before running your routine.

Answer 2

As mentioned by #david-wolfe, AutoCAD 2015 may start with no active document (just a dashboard). In this case the MdiActiveDocument can be null.
Now you're on AutoCAD 2014, so a different scenario may happen: if your app is loading with AutoCAD, you code may run before anything is really ready. How are you running the code? Is it a CommandMethod? If is a command, the user can only run it from a command, so it will be a active document. But if you run it from other method (like direct call from the Ribbon or from a palette), it may be null.