C#•2y ago

✅ Cant convert a list to list of a class type?

I am new to C# and am stuck on this strange issue, I cant seem to send a list to a different class, as its only accepting a list of type "Customer" (class name), how would I convert or send this information over? Method which collects info and sends it to save method

public partial class frmCustomers : Form
    {
        List<Customer> customers = new List<Customer>();

        private void btnAdd_Click(object sender, EventArgs e)
        {
            frmAddCustomer addCustomerForm = new frmAddCustomer();
            Customer customer = addCustomerForm.GetNewCustomer();
            if (customer != null)
            {
                CustomerDB.SaveCustomers(customer); /// This is the line giving me an error
                MessageBox.Show(customer.GetDisplayText().ToString(), "BTNAddClick2");
                CustomerListBox();
                
            }
        }

public partial class frmCustomers : Form
    {
        List<Customer> customers = new List<Customer>();

        private void btnAdd_Click(object sender, EventArgs e)
        {
            frmAddCustomer addCustomerForm = new frmAddCustomer();
            Customer customer = addCustomerForm.GetNewCustomer();
            if (customer != null)
            {
                CustomerDB.SaveCustomers(customer); /// This is the line giving me an error
                MessageBox.Show(customer.GetDisplayText().ToString(), "BTNAddClick2");
                CustomerListBox();
                
            }
        }

Save Method: will be posted as a comment so I dont run out of available words.

3 Replies

bernie2024•2y ago

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));
            foreach (Customer customer in customers)
            {
                MessageBox.Show(customer.FirstName + customer.LastName + customer.Email, "SaveCustomers1");
            }

            // write each customer
            foreach (Customer customer in customers)
            {
                if (customer == null)
                {
                    MessageBox.Show("2, 3");
                    throw new ArgumentNullException(nameof(customer), "Customer object cannot be null");
                }

                MessageBox.Show("2, 4");
                textOut.Write(customer.FirstName + "|");
                textOut.Write(customer.LastName + "|");
                textOut.WriteLine(customer.Email);
                MessageBox.Show(customer.FirstName + customer.LastName + customer.Email, "SaveCustomers1");
            }

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

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));
            foreach (Customer customer in customers)
            {
                MessageBox.Show(customer.FirstName + customer.LastName + customer.Email, "SaveCustomers1");
            }

            // write each customer
            foreach (Customer customer in customers)
            {
                if (customer == null)
                {
                    MessageBox.Show("2, 3");
                    throw new ArgumentNullException(nameof(customer), "Customer object cannot be null");
                }

                MessageBox.Show("2, 4");
                textOut.Write(customer.FirstName + "|");
                textOut.Write(customer.LastName + "|");
                textOut.WriteLine(customer.Email);
                MessageBox.Show(customer.FirstName + customer.LastName + customer.Email, "SaveCustomers1");
            }

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

Error reads: "Cannot convert from type 'CustomerMaintenence.Customer' to 'Systems.Collections.Generic.List<CustomerMaintence.Customer>' Ignore the messageboxes, they are debugging code as I am 4 hours deep into this and no closer to getting it running.

jcotton42•2y ago

you're trying to convert from a single thing to a list of things you either meant to pass a List, or you need to wrap what you're passing in a List

bernie2024•2y ago

I DID IT sorry man I didnt mean to waste your time so I found the issue was I needed to do a customers.Add(customer); which is adding it to a list of type Customer now it can send over which would be the passing to to a list which you were talking about ok thank you very much sorry again wow bad timing on my part

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✅ Cant convert a list to list of a class type?