C#•3y ago

❔ ✅ Struggling with function showing error, "Object reference not set to an instance of an object"

have been trying to solve this issue, not sure what the problem is. public static class CustomerDB
{
private const string dir = @"C:\C#\Files";
private const string path = dir + "Customers.txt";
public static void SaveCustomers(List<Customer> customers)
{
// create the output stream for a text file that exists
StreamWriter textOut =
new StreamWriter(
new FileStream(path, FileMode.Create, FileAccess.Write));

// write each customer
foreach (Customer customer in customers)
{
textOut.Write(customer.FirstName + "|");
textOut.Write(customer.LastName + "|");
textOut.WriteLine(customer.Email);
}

// write the end of the document
textOut.Close();
}
I get the error "Exception Thrown System.NullReferenceException: 'Object reference not set to an instance of an object. customers was null."

If any additional reference code is needed for context I can provide it, the point of this is to add a "Customer" to a database of customers

What am I doing wrong here? it only has the issue once reaching the 'Foreach (Customer customer in customers)' statement.

Angius•1/27/23, 1:37 AM

customers = null;customers = null;

Angius•1/27/23, 1:37 AM

You set the list of customers to nullnull

bernie2024OP•1/27/23, 1:37 AM

sorry

Angius•1/27/23, 1:37 AM

Then you're trying to access things from it

bernie2024OP•1/27/23, 1:37 AM

I had deleted that line and forgot it

bernie2024OP•1/27/23, 1:37 AM

without that line

bernie2024OP•1/27/23, 1:37 AM

it still produces the same error

bernie2024OP•1/27/23, 1:37 AM

ill add a screenshot for greater context

bernie2024OP•1/27/23, 1:37 AM

bernie2024OP•1/27/23, 1:38 AM

public static void SaveCustomers(List<Customer> customers)
{
// create the output stream for a text file that exists
StreamWriter textOut =
new StreamWriter(
new FileStream(path, FileMode.Create, FileAccess.Write));

// write each customer
foreach (Customer customer in customers)
{
if (customer == null)
{
throw new ArgumentNullException(nameof(customer), "Customer object cannot be null");
}
textOut.Write(customer.FirstName + "|");
textOut.Write(customer.LastName + "|");
textOut.WriteLine(customer.Email);
}

// write the end of the document
textOut.Close();
}

Angius•1/27/23, 1:38 AM

And where do you call this method?

bernie2024OP•1/27/23, 1:38 AM

I have rewritten this multiple times, is the issue that I need to initialize the list beforehand?

Angius•1/27/23, 1:38 AM

Also, $code

AAngius Also, $code

MODiX•1/27/23, 1:38 AM

To post C# code type the following:
```cs
// code here
```

Get an example by typing

$codegif

$codegif

in chat

If your code is too long, post it to: https://paste.mod.gg/

bernie2024OP•1/27/23, 1:38 AM

I am calling this method from a form Add button

bernie2024OP•1/27/23, 1:39 AM

ill post it

Angius•1/27/23, 1:40 AM

` not '

Angius•1/27/23, 1:40 AM

The key under EscEsc

Angius•1/27/23, 1:40 AM

That said, I don't see SaveCustomersSaveCustomers being called anywhere

bernie2024OP•1/27/23, 1:40 AM

im stupid asf

bernie2024OP•1/27/23, 1:40 AM

sorry

bernie2024OP•1/27/23, 1:40 AM

its been a long day here we go

bernie2024OP•1/27/23, 1:41 AM

private void btnAdd_Click(object sender, EventArgs e)
        {
            frmAddCustomer addCustomerForm = new frmAddCustomer();
            Customer customer = addCustomerForm.GetNewCustomer();
            if (customer != null)
            {
                CustomerDB.SaveCustomers(customers);
                CustomerListBox();
            }
        }

private void btnAdd_Click(object sender, EventArgs e)
        {
            frmAddCustomer addCustomerForm = new frmAddCustomer();
            Customer customer = addCustomerForm.GetNewCustomer();
            if (customer != null)
            {
                CustomerDB.SaveCustomers(customers);
                CustomerListBox();
            }
        }

Angius•1/27/23, 1:41 AM

Chances are, it is at this point that customerscustomers is nullnull

bernie2024OP•1/27/23, 1:42 AM

so the error is referencing the point where its being called

bernie2024OP•1/27/23, 1:42 AM

I do initialize the list in this class

bernie2024OP•1/27/23, 1:42 AM

bernie2024OP•1/27/23, 1:42 AM

its initialized as null, but as a local variable

Angius•1/27/23, 1:42 AM

There's no local variable customerscustomers tho

bernie2024OP•1/27/23, 1:44 AM

im sorry I dont think I understand

Angius•1/27/23, 1:44 AM

The field customerscustomers is nullnull

Angius•1/27/23, 1:44 AM

So you pass nullnull to your method

Angius•1/27/23, 1:44 AM

That's where it comes from

bernie2024OP•1/27/23, 1:44 AM

so I should initialize it as an empty list and not a null list

Angius•1/27/23, 1:44 AM

For example, yes

bernie2024OP•1/27/23, 1:45 AM

ok thank you very much! I will try that

bernie2024OP•1/27/23, 1:45 AM

I must have gotten confused and thought null was the same as empty

Angius•1/27/23, 1:45 AM

Could be

Angius•1/27/23, 1:45 AM

If you're using .NET 6 or newer, be sure to enable nullable reference types

Angius•1/27/23, 1:46 AM

They help you figure out errors of this kind

Angius•1/27/23, 1:46 AM

For example, a List<int>List<int> cannot be nullnull, you need to explicitly use List<int>?List<int>? to allow for it being nullnull

Angius•1/27/23, 1:46 AM

etc

bernie2024OP•1/27/23, 1:51 AM

when I swap the null customers for: List<Customer> customers = new List<Customer>();

bernie2024OP•1/27/23, 1:51 AM

when initializing it

bernie2024OP•1/27/23, 1:51 AM

I still get the same error

Angius•1/27/23, 1:53 AM

odd

bernie2024OP•1/27/23, 1:53 AM

hold on

Angius•1/27/23, 1:53 AM

Run the debugger ig

Angius•1/27/23, 1:53 AM

Place some breakpoints

bernie2024OP•1/27/23, 1:53 AM

ok thank you friend

❔ ✅ Struggling with function showing error, "Object reference not set to an instance of an object"

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