C#•8mo ago

✅ Object Reference is null, even with try/catch

What dumb thing could I be missing? I'm trying to add a custom object to a simple dictionary of string + custom object. In the debug, you'll see that the

_storedPoints

_storedPoints

_storedPoints

_storedPoints is not null, and the

modifiedRow

modifiedRow

modifiedRow

modifiedRow is not null. While not shown,

modifiedRow.Name

modifiedRow.Name

modifiedRow.Name

modifiedRow.Name is not null either. Could it be that this error is caught on another thread (since this is from a Parallel.ForEach), and I'm just not seeing the correct object in my debug?

reflectronic•4/28/25, 9:46 PM

what is

_storedPoints

_storedPoints

engineertdogOP•4/28/25, 9:46 PM

reflectronic•4/28/25, 9:46 PM

yes, this would be a problem

reflectronic•4/28/25, 9:46 PM

you cannot modify a Dictionary from multiple threads at the same time

reflectronic•4/28/25, 9:47 PM

an otherwise inexplicable NullReferenceException is exactly what i would expect to see if you did this

engineertdogOP•4/28/25, 9:47 PM

It only has issues on the first time running when I populate the SQLite database. Otherwise it's fine.

reflectronic•4/28/25, 9:47 PM

it does not change the fact that you are not allowed to do it

reflectronic•4/28/25, 9:48 PM

the code in Dictionary assumes that you will not do it. if you violate these assumptions, it will create unexplainable errors at unpredictable times, like this one

engineertdogOP•4/28/25, 9:48 PM

I'm not sure why I'm still doing this anyway, apart from SQL performance. I need to query the SQLite database for each row rather than using memory to find these items.

reflectronic•4/28/25, 9:49 PM

you can use a class like https://learn.microsoft.com/en-us/dotnet/api/system.collections.concurrent.concurrentdictionary-2?view=net-9.0 instead

ConcurrentDictionary Class (System.Collections.Concurrent)

Represents a thread-safe collection of key/value pairs that can be accessed by multiple threads concurrently.

engineertdogOP•4/28/25, 9:50 PM

Yeah, I could use that as a bypass until I get this reworked. This will work for small systems with less than 500k rows, but the systems that have 5 million rows is going to be problematic with this approach.

engineertdogOP•4/28/25, 11:59 PM

Not sure how, but this can be marked closed.