Question

I’m learning C# from a book and i’m expanding on an example in an effort to better understand the syntax.

I’m trying to use the following code to cycle through a collection of objects and pick out only certain ones so I can load them into a separate array. I’m struggling with this particular line right now:

if (animalCollection[i].Equals(Chicken))

Here is the complete code for Program.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Ch11Ex02
{
class Program
    {
    static void Main(string[] args)
        {
        Animals animalCollection = new Animals();
        animalCollection.Add(new Cow("Jack"));
        animalCollection.Add(new Chicken("Vera"));
        animalCollection.Add(new Chicken("Sally"));

        Animal[] birds = new Animal[2];
        for (int i = 0; i < animalCollection.Count; i++)
            {
            if (animalCollection[i].Equals(Chicken))
                birds[i] = animalCollection[i];
            }

        foreach (Animal myAnimal in animalCollection)
            {
            myAnimal.Feed();
            }
        Console.ReadKey();
        }
    }
}

My goal is to load only object types Chicken into a new array called birds.

here is the code for class Animal:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Ch11Ex02
{
public abstract class Animal
    {
    protected string name;

    public string Name
        {
        get
            {
            return name;
            }
        set
            {
            name = value;
            }
        }

    public Animal()
        {
        name = "The animal with no name";
        }

    public Animal(string newName)
        {
        name = newName;
        }

    public void Feed()
        {
        Console.WriteLine("{0} has been fed." , name);
        }

    internal bool equals()
        {
        throw new NotImplementedException();
        }
    }
}

and here is the code for class Chicken:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Ch11Ex02
{
public class Chicken : Animal
    {
    public void LayEgg()
        {
        Console.WriteLine("{0} has laid an egg." , name);
        }
    public Chicken(string newName): base(newName)
        {
        }
    }
}

and here is the code for class Animals:

using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Ch11Ex02
{
public class Animals : CollectionBase
    {
    public void Add(Animal newAnimal)
        {
        List.Add(newAnimal);
        }

    public void Remove(Animal newAnimal)
        {
        List.Remove(newAnimal);
        }

    public Animals()
        {
        }

    public Animal this[int animalIndex]
        {
        get
            {
            return (Animal)List[animalIndex];
            }
        set
            {
            List[animalIndex] = value;
            }
        }
    }
}

Answer 1

Fundamentals

To determine whether an object is of a given type, you can use typeof or is

if (typeof(someObject) == typeof(Chicken))

or

 if (someObject is Chicken)

so specifically in your case

if (animalCollection[i].Equals(Chicken))

becomes

if (typeof(animalCollection[i]) == typeof(Chicken))

or

if (animalCollection[i] is Chicken)

You can also determine an object’s type like this

Type t = animalCollection[i].GetType();

The Fast Way

Now that I have covered how this works at a basic level, here’s a way to accomplish the same in one line, using Linq

var chickens = animals.OfType<Chicken>().ToArray();

By the Way

If you then wanted to get the type name as a string, you could do this

string typeName = t.FullName;