Respect to all those POS developers. It really requires some dedication and focus to be a POS developer. This is an example of something I would have not figured out without my colleagues.
We were working on a development project and we struggled to make sense out of the error.
The error we got was complaining about the a method to validate the Unit of measure and Quantity. I was sure the object was not null and I had passed the right thing to it. Unit of measure and quantity fields were populated correctly. The modification was overriding the price.
System.NullReferenceException was unhandled by user code
After many hours over the course a few days we struggled. A colleague suggested to use .NET reflector (this is where you need an experienced retail developer). Using this tool, I was able to make sense of the problem.
Below are the steps to use .NET reflector.
1. Download .NET reflector
2. Install following wizard. You can use the trial for 14 days or just active it with your serial number
When you install – I would recommend both the desktop and the visual studio extension
3. Select the assembly to debug. There are a couple of ways you can do that.
Select using the .NET Reflector > Generate PDBs (this will pop up a dialog to select the assembly)
4. This will launch the object browser.
Navigate to the method that caused the error. Then right click, Go to Decompiled Definition
5. I put a breakpoint and run through the process.
What I found was that it code used the salesTransaction object rather than the cartLine to get the unit of measure. Causing a cryptic error about unit of measure/quantity. In other words, I needed to create the cart line and save it to commit it to the salesTransaction first. Then after that process is finished, I can then override the price. i.e. 2 steps rather than trying to it all in one process.
I hope I don’t get in trouble of advising people to use .NET reflector by blogging here. I just don’t see how else I would have figure this thing out.