Newbie here. Why is my array list not working?

Marc Hede

I am very new to ASP.net and C#, so I am trying my best, but there are stille many things that confuse me, especially because when I am looking at various examples online they give me different answers to the same solution, which just makes it even more confusing. I made a person class, with two subclasses (driver and admin), but I can not get the ArrayList to show up when I run my Index file. I only get a parse error. What do I need to change to make this work? My person class

public class Person
{
public Person(string firstName, string lastName, int age, string email)
{
FirstName = firstName;
LastName = lastName;
Age = age;
Email = email;
}
public string FirstName { get; set; }
public string LastName { get; set; }
public int Age { get; set; }
public string Email { get; }
public virtual bool ChangeEmail(string email)
{
Email = email;
return true;
}
public override string ToString()
{
return $"Name: {FirstName} {LastName}, Age: {Age}, E-mail: {Email}";
}
}

My subclasses

public class Driver : Person
{
private string v1;
private string v2;
private string v3;
private string v4;
private string v5;
public Driver(string firstName, string lastName, int age, string email, int
licenceNumber)
: base(firstName, lastName, age, email)
{
LicenceNumber = licenceNumber;
}
public Driver(string v1, string v2, string v3, string v4, string v5)
{
this.v1 = v1;
this.v2 = v2;
this.v3 = v3;
this.v4 = v4;
this.v5 = v5;
}
public int LicenceNumber { get; set; }
public override string ToString()
{
return $"Role: Traindriver, LicenceNumber: {LicenceNumber}, " + base.ToString();
}
}
public class Admin : Person
{
public Admin(string firstName, string lastName, int age, string email)
: base(firstName, lastName, age, email)
{
}
public override bool ChangeEmail(string email)
{
if (!email.EndsWith("@pig.dk", StringComparison.InvariantCultureIgnoreCase))
return false;
return base.ChangeEmail(email);
}
public override string ToString()
{
return $"Role: Admin, " + base.ToString();
}
}
}

My ArrayList

namespace Pig
{
public partial class Index : System.Web.UI.Page
{
public object ListBoxResults { get; private set; }
public object DriverListBox { get; private set; }
protected void Page_Load(object sender, EventArgs e)
{
Driver d1 = new Driver("Hans", "Christensen", 32, "hans@pig.dk", 123456);
Driver d2 = new Driver("Peter", "Jensen", 40, "

phil o

Please indicate the exact error message, as well as the line which is triggering it. "Not working" is not precise enough.

"Five fruits and vegetables a day? What a joke! Personally, after the third watermelon, I'm full."

Richard Deeming

You have a control with the ID ListBoxResults, which will automatically generate a field in your class:

private ListBox ListBoxResults;

You have also declared a property called ListBoxResults in your code-behind. I'd be extremely surprised if that code compiled; if it did, your references to ListBoxResults in your Page_Load method would be referring to the property, not the control. Remove the property and your code should start working:

namespace Pig
{
public partial class Index : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
Driver d1 = new Driver("Hans", "Christensen", 32, "hans@pig.dk", 123456);
Driver d2 = new Driver("Peter", "Jensen", 40, "peter@mail.dk", 123456);
Admin a1 = new Admin("Lene", "Maarud", 55, "lene@pig.dk");
ListBoxResults.Items.Add(d1.ToString());
ListBoxResults.Items.Add(d2.ToString());
ListBoxResults.Items.Add(a1.ToString());
}
}
}

"These people looked deep within my soul and assigned me a number based on the order in which I joined." - Homer

Marc Hede

Okay, I removed the property and also changed "ListBoxResults" to simply "ListBox". There are some problems remaining. I will list the errors here (sorry for not doing so at first)

        ListBox.Items.Add(d1.ToString());
        ListBox.Items.Add(d2.ToString());
        ListBox.Items.Add(a1.ToString());

Here I get the error: "An object reference is required for the non-static field, method, or property." If I remember correctly, a solution to this would be to make a static ArrayList, but I am not sure how I can do it for this code. Error no. 2

public virtual bool ChangeEmail(string email)
{
Email = email;
return true;
}

Error: "Property or indexer cannot be assigned to -- it is read only"

Error no. 3

    public Driver(string v1, string v2, string v3, string v4, string v5)
    {
        this.v1 = v1;
        this.v2 = v2;
        this.v3 = v3;
        this.v4 = v4;
        this.v5 = v5;
    }

Error message: There is no argument given that corresponds to the required formal parameter of 'firstName' of 'Person.Person (string, string, int, string)'

Thanks a ton for being patient with me, you guys.

Richard Deeming

Member 14671427 wrote:

and also changed "ListBoxResults" to simply "ListBox"

Which is not what I said, and is the cause of the "object reference required" errors. Remove the property; leave the Page_Load method as I showed you:

namespace Pig
{
public partial class Index : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
Driver d1 = new Driver("Hans", "Christensen", 32, "hans@pig.dk", 123456);
Driver d2 = new Driver("Peter", "Jensen", 40, "peter@mail.dk", 123456);
Admin a1 = new Admin("Lene", "Maarud", 55, "lene@pig.dk");
ListBoxResults.Items.Add(d1.ToString());
ListBoxResults.Items.Add(d2.ToString());
ListBoxResults.Items.Add(a1.ToString());
}
}
}

Member 14671427 wrote:

Error: "Property or indexer cannot be assigned to -- it is read only"

You haven't added a setter to the Email property, so you can't set it. If you don't want to be able to change it from outside of the class, then make the setter private:

public string Email { get; private set; }

Member 14671427 wrote:

There is no argument given that corresponds to the required formal parameter of 'firstName' of 'Person.Person (string, string, int, string)'

Your Person constructor requires four arguments. Every constructor of a class derived from Person must pass those four arguments into the base constructor.

public Driver(string v1, string v2, string v3, string v4, string v5)
: base("??? FIRST NAME ???", "??? LAST NAME ???", 0, "??? EMAIL ???")

"These people looked deep within my soul and assigned me a number based on the order in which I joined." - Homer

Marc Hede

Hi again and thanks once again. I did do ask you said. The reason why I tried playing around with the ListBox line is because I am getting an CS0103 error: "The name ListBoxResults does not exist in the current context", which I don't get, because I looked in my index file. It says

I checked if the namespace was the issue, but that was not that case. However, the object reference error is gone, just like you said =)

Richard Deeming

That would suggest that your .aspx markup file isn't correctly tied to your .aspx.cs code-behind file. Check the CodeFile / CodeBehind and Inherits attributes on the <%@ Page ... %> directive in your markup file. @ Page | Microsoft Docs[^]

"These people looked deep within my soul and assigned me a number based on the order in which I joined." - Homer

Marc Hede

Ah, what an idiot I was. In Inhereits, I had written "index" instead of "Index". Thanks a lot for helping me =)