How to fix System.NullReferenceException: 'Object variable or With block variable not set.'

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How to fix System.NullReferenceException: 'Object variable or With block variable not set.'

Stephen H. Jones 40

Working Visual Studio Pro 2019, project is .NET Framework 4.72

I have a design window with several numeric input objects. I deleted one and recreated it but now I get this error when I test the solution. It builds just fine and shows no errors in the code windows but when I open this window in the app, it fails with this message pointing to the code of this newly recreated object. I have tried everything I can think of to cure this issue but nothing seems to work.

Please HELP!

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Answer 1

Michael Taylor 57,476

You'll need to share the code with us along with the exception details including the message and stacktrace. Without that we have no idea what is wrong.

Just off the top of my head you most likely have a field that isn't set and your code is referencing it which triggers a NRE. In general you should only ever delete things via the designer. If you deleted it in code then that tends to lead to problems like this. But, again, just a guess with no other information.

When the error occurs you'll get thrown into the debugger. At that point you have the exact line that is failing and one of the instances on that line is null. You then need to figure out why. It could be because you deleted some controls or it could be something completely unrelated. The debugger will show you what is bad though. Fix the code by ensuring you either handle cases where the instance is null or by ensuring the value is never null.

Stephen H. Jones 40 Reputation points

2024-08-10T18:44:54.7566667+00:00

It turns out that when I had deleted a numeric input object and then recreated it, I had mistakenly omitted the first letter of its name, so now everywhere it was used in the code, it was undefined. Then when I tried to build it it errored, and one of the suggested cures was to define this misspelled name as a Private device in the form code. After that it built correctly but when I tested the app it would fail when I opened that form because the object had no real meaning.

When I discovered the missing first character in the name of the object, it built correctly and also test ran without errors.

BTW, no matter WHAT I did last night to see your response (after I was alerted in an email that you had responded), I was never able to see your response here! Your response only showed up just now when I went back to my email again and clicked on the "See the answer" button. WTF is with THAT????

In any event, thanks for trying to help.

I joined the r/VisualStudio Reddit subgroup this morning where I described all of this and LOTS more about my frustrations with trying to get assistance from the Microsoft resources. My user name is u/Shjco so look it up for more "good" stuff about this experience. I hop the folks at Microsoft also see it because it talks in detail about a faulty part of THEIR web site programming.

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How to fix System.NullReferenceException: 'Object variable or With block variable not set.'

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