topic Re: Null Reference Exception in Inventor Programming Forum

Null Reference Exception

jpchaisson — Wed, 18 May 2022 20:24:28 GMT

its been a few years since ive gotten my hands dirty with writing code for Inventor and im getting an error when i test a few lines of code and i cant figure out why. if i open old projects and run the code everything works. so i have a Drawing open in Inventor and i have two custom iProperties on the drawing that is blank at the moment and i have a small vb.net UI with a button, when i click the button im trying to populate the custom iProperties with values hard coded just as a test to get the code correct. Line 4 throws me a Null Reference Exception. can anyone explain what im missing?

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click

Dim oStation As String = "Test"
Dim oStationID As String = "Test ID"

Dim oApp As Inventor.Application = GetObject(, "Inventor.Application")
Dim oDoc As DrawingDocument = oApp.ActiveDocument '<-------Problem Line-----

Dim oCustomiProp As PropertySet
oCustomiProp = oDoc.PropertySets.Item("Inventor User Defined Properties")

oCustomiProp.Item("Station").Value = oStation

End Sub

Re: Null Reference Exception

dalton98 — Wed, 18 May 2022 21:24:37 GMT

Dim oObj As String = "Inventor.Application"
Dim oApp As Inventor.Application = GetObject(, oObj)
Dim oDoc As DrawingDocument
oDoc = oApp.ActiveDocument

Re: Null Reference Exception

jpchaisson — Thu, 19 May 2022 03:16:53 GMT

Still getting a Null Reference.... i am really confused this is such a simple line of code and ive never gotten this before.

Re: Null Reference Exception

dalton98 — Thu, 19 May 2022 12:29:47 GMT

I'm not familiary with VBA, but I believe you need to write 'Set' in front of new objects. This is an example from the api helper. It can be found by clicking the drop down for the (?) in the top right > Help > Programming/API help.

Public Sub CreateCustomTable()
    ' Set a reference to the drawing document.
    ' This assumes a drawing document is active.
    Dim oDrawDoc As DrawingDocument
    Set oDrawDoc = ThisApplication.ActiveDocument

Re: Null Reference Exception

jpchaisson — Thu, 19 May 2022 14:57:12 GMT

This is VB.NET not VBA

Ive never had this problem before. its driving me crazy. everything looks correct

Re: Null Reference Exception

dalton98 — Fri, 20 May 2022 18:46:41 GMT

Follow this link:

https://knowledge.autodesk.com/search-result/caas/simplecontent/content/lesson-1-the-basic-plug--E2-80-93-autodesk-inventor.html

I copy and pasted ur code and it worked fine.

Re: Null Reference Exception

WCrihfield — Fri, 20 May 2022 18:44:49 GMT

Hi @jpchaisson. It is possible to have the Inventor application open, without actually having any documents open. Could that possibly be the case here? Then there is the situation where you might have multiple instances of Inventor open...one with 1 or more documents open, and the other with no documents open, and maybe your code is grabbing the instance without any open documents. Just throwing some stuff out there.

Re: Null Reference Exception

JelteDeJong — Sat, 21 May 2022 10:27:57 GMT

try replacing the line:

Dim oApp As Inventor.Application = GetObject(, "Inventor.Application")

with the following:

Dim oApp As Inventor.Application = System.Runtime.InteropServices.Marshal.GetActiveObject("Inventor.Application")