C#•10mo ago

Get first item in list

I am having a very strange bug with my List<> The following code works as intended - resulting tallyTotal of first person in possiblePeople :

c#
{
            Person selectedPerson;
            List<Person> possiblePeople = new List<Person>();

            foreach (Person person in people)
            {
                if(person.tallyTotal == Person.tallyBaseline)
                {
                    possiblePeople.Add(person);
                }
            }
            possiblePeople.Sort((x, y) => string.Compare(x.lastName, y.lastName));

            consoleOutput.Text = possiblePeople[0].tallyTotal.ToString();
}

c#
{
            Person selectedPerson;
            List<Person> possiblePeople = new List<Person>();

            foreach (Person person in people)
            {
                if(person.tallyTotal == Person.tallyBaseline)
                {
                    possiblePeople.Add(person);
                }
            }
            possiblePeople.Sort((x, y) => string.Compare(x.lastName, y.lastName));

            consoleOutput.Text = possiblePeople[0].tallyTotal.ToString();
}

just changing the last line breaks it:

c#
possiblePeople[0].tallyTotal += 1;

c#
possiblePeople[0].tallyTotal += 1;

it provides the attached error (image)

28 Replies

TheBoxyBear•10mo ago

Does it rub the adding of items? Check with a breakpoint and checking the contents of the list once stoped

Pobiega•10mo ago

yeah verify the number of items in possiblePeople before using it your code does not take the posibility of no person in people having that tally I would personally use var firstPerson = possiblePeople.FirstOrDefault(); and check that for null before trying to modify the value

milanOP•10mo ago

let me try that real quick I don't know how it would be possible for possiblePeople to be empty, but I'll give it a go

Pobiega•10mo ago

well you should verify with the debugger, as BoxyBear suggested

milanOP•10mo ago

I'm using visual studio, not visual studio code, as this is a WPF project

Pobiega•10mo ago

sure, I dont see how that changes anything I just said lol VS has a very capable debugger built in

milanOP•10mo ago

oh, I'm not too familiar with VS... I'll have to play around with it for a bit I'll just try this first

Pobiega•10mo ago

$debug

MODiX•10mo ago

https://docs.microsoft.com/en-us/visualstudio/get-started/csharp/tutorial-debugger?view=vs-2022

Tutorial: Debug C# code and inspect data - Visual Studio (Windows)

Learn features of the Visual Studio debugger and how to start the debugger, step through code, and inspect data in a C# application.

milanOP•10mo ago

Ok i tested it there definitely IS a person at index 0 i will send a series of screenshots

Pobiega•10mo ago

and tallyTotal is just a public int property?

milanOP•10mo ago

yup

Pobiega•10mo ago

if you run the program with the debugger attached but with no breakpoints, it should break when the exception is thrown (possibly thats what we are already looking at in the last screenshot)

milanOP•10mo ago

c#
    public class Person
    {
        public int id;
        public string firstName = "Doc";

        public int tallyTotal = 0;


        public Person(string FirstName, string LastName) 
        { 
            firstName = FirstName;
            lastName = LastName;

            id = personCount;
            personCount++;
        }
    }

c#
    public class Person
    {
        public int id;
        public string firstName = "Doc";

        public int tallyTotal = 0;


        public Person(string FirstName, string LastName) 
        { 
            firstName = FirstName;
            lastName = LastName;

            id = personCount;
            personCount++;
        }
    }

Person object (heavily simplified)

Pobiega•10mo ago

you can then inspect the possiblePeople variable there those are fields, not properties fyi not the cause of your problem, but should be fixed

milanOP•10mo ago

oh yeah my bad welp it is empty

Pobiega•10mo ago

🙂

milanOP•10mo ago

for whatever reason between these two lines of code it becomes empty

milanOP•10mo ago

Pobiega•10mo ago

your code runs several times then

milanOP•10mo ago

let me double check that I'm doing something very stupid here

Pobiega•10mo ago

and it works once or more, then fails at a later time

milanOP•10mo ago

I can't imagine how that's possible the code runs when a WPF button is pressed just once the function is called this project is VERY bare bones right now

Pobiega•10mo ago

hm, well unless you have shared mutable state for this class, thats the only explanation I can come up with can you share the full source somewhere? github?

milanOP•10mo ago

ah you're right actually the code is nested in a foreach loop, and it looks like it does work the first few times, but then breaks at the end. I didnt notice/forgot about the loop because it happens instantly... woops well tysm

Pobiega•10mo ago

🙂

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Get first item in list