Adding object to a list, changes all other list objects

Question

I’m trying to add animals to my animal list, but the values of the last added animal will be all the animals in the list.

List<Animal> animals = new List<Animal>();
public bool AddAnimal(Animal animal)
        {
            animals.Add(animal); 
            return true;
        } 

Animal animal = new Animal();
private void btnAddAnimal_Click(object sender, RoutedEventArgs e)
        {
            animal.AnimalSize = Size.large;
            animal.Carnivore = true;
            AddAnimal(animal);
        }

This is the list: Size Carnivore - Large True

private void btnAddAnimal_Click(object sender, RoutedEventArgs e)
        {
            animal.AnimalSize = Size.large;
            animal.Carnivore = false;
            AddAnimal(animal);
        }

This is what happens with my animals list after I add an Herbivore:

• Size Carnivore
  • Large false
  • Large false

Answer 1

Well, you don't actually add a new Animal, you're merely modifying the one you have. If you want to add a new animal, you have to create a new object:

private void btnAddAnimal_Click(object sender, RoutedEventArgs e)
{
  Animal animal = new Animal();
  animal.AnimalSize = Size.large;
  animal.Carnivore = true;
  AddAnimal(animal);
}