Problem with object reference and static methods

Chris Anderson

I'm trying to invoke a method from another class. Either way, having it static or non-static, I run into errors and don't know how to proceed. Animal.cs is an abstract class which complicate things when speaking of object references.

I've stripped the code down keeping the most essential parts (I think).

Application.cs
This is the class that holds a menu from which I call the static BuyToy method.

class Application
{
public static void Menu()
{
Animal.BuyToy();
}
}

Animal.cs
Line 34 and 35 throw errors when method is static. By removing static errors disappear and I'm able to reach both the Name and Toys list. But then instead I won't be able to call the BuyToy method from Application.cs

abstract class Animal
{
public string Name { get; set; }
public List Toys { get; set; } = new List();
public static void BuyToy()
{
Toy ball = new Ball();
Toy bone = new Bone();
Toy feather = new Feather();
Console.WriteLine("Select which toy you want to buy");
Console.WriteLine("[1] Ball");
Console.WriteLine("[2] Bone");
Console.WriteLine("[3] Feather");
buyMenu = int.Parse(Console.ReadLine());
switch (buyMenu)
{
case 1:
selectedToy = ball;
break;
case 2:
selectedToy = bone;
break;
case 3:
selectedToy = feather;
break;
default:
break;
}
Toys.Add(selectedToy); // Gives the error "An object reference is required for the non-static field, method, or property 'Animal.Toys'.
Console.WriteLine("You just bought a new" + selectedToy + " for" + Name + " fully loaded with max quality of 10"); // Gives the error "An object reference is required for the non-static field, method, or property 'Animal.Name'
break;
case 2:
Application.Menu();
break;
default:
break;
}
}
}

6 Replies

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Sachin Singh5y ago
create list inside method.
abstract class Animal
    {
        public string Name { get; set; }
        public List Toys { get; set; } ;

        public static void BuyToy()
        {
             Toys=new List();
                    Toy ball = new Ball();
                    Toy bone = new Bone();
                    Toy feather = new Feather();

                    Console.WriteLine("Select which toy you want to buy");
                    Console.WriteLine("[1] Ball");
                    Console.WriteLine("[2] Bone");
                    Console.WriteLine("[3] Feather");

                    buyMenu = int.Parse(Console.ReadLine());

                    switch (buyMenu)
                    {
                        case 1:
                            selectedToy = ball;
                            break;
                        case 2:
                            selectedToy = bone;
                            break;
                        case 3:
                            selectedToy = feather;
                            break;
                        default:
                            break;
                    }
                    Toys.Add(selectedToy);
                    Console.WriteLine("You just bought a new" + selectedToy + " for" +  Name  + " fully loaded with max quality of 10");  // Gives the error "An object reference is required for the non-static field, method, or property 'Animal.Name'
                    break;
                case 2:
                    Application.Menu();
                    break;
                default:
                    break;
            }
        }
    }
0
Chris Anderson5y ago
Thanks for the reply!

Since I want to create a new Toys list for every animal static won't be the way to go right? If I get it right static means it's one instance of the list? Which means if I edit the list for one animal it will be edited for all animals?
+1
Amit Gupta5y ago
Okay,,, Got it

You had declared a List datatype to add Toys,

Change from
public List Toys { get; set; } = new List();
to
public static List Toys { get; set; } = new List();
Do let me know if the issue still persist.
+1
Chris Anderson5y ago
Thanks for your answers!

Having the class Animal.cs as abstract is a must since it's part of the assignment. Which indeed makes things more complicated.

Also, adding static to the properties won't let me create instances which are needed in order to create more animals.

I would rather go with the non-static context but the abstract class won't let me.

I'm lost, either way I'll hit a roadbump which is so frustrating... :(
+1
Ben Thompson5y ago
Depending on your application needs, there are two different ways you can handle this.
First, you can convert the application to a static context. As it is, when BuyToy() is static, it can only access methods and variables which are also static. (And technically, constant). In your case, the List at line 34 being added to isn't static, hence the error. Likewise, Name being referenced isn't static as well. Therefore for line 3-4:
public static string Name { get; set; }
public static List Toys { get; set; } = new List();

Alternatively, you can convert your application to a non-static context, create an instance of Animal, then call BuyToy() off that instance. You'll need to remove the "abstract" modifier on line 1 and the "static" modifier on line 6. Then, in application.cs:
Animal animal = new Animal();
animal.BuyToy();
This creates an instance of Animal called animal, and calls the BuyToy() method of that specific instance.
+1
Amit Gupta5y ago
Either make it static
public static List Toys { get; set; } = new List();
or remove static
public static void BuyToy()
to
public void BuyToy()
+1