Adding a animal/dog/cat to a animal list results in NullReferenceException?

Question

I have two subclasses of animal (dog which has a last walk date as extra value and cat which has a bad habbit as a extra value) in the code below i create either a cat or a dog

public partial class AdministrationForm : Form
{
    private Animal animal;
    private Administration admin;

    public AdministrationForm()
    {
        InitializeComponent();
        animalTypeComboBox.SelectedIndex = 0;
        animal = null;
    }

    private void createAnimalButton_Click(object sender, EventArgs e)
    {
        if(animalTypeComboBox.SelectedItem == "Dog")
        {
            SimpleDate dateBirth = new SimpleDate(ttbdateBirth.Value.Day,
            ttbdateBirth.Value.Month,
            ttbdateBirth.Value.Year);
            SimpleDate dateLast1 = new SimpleDate(dateLast.Value.Day, dateLast.Value.Month, dateLast.Value.Year);
            Animal animal = new Dog(Convert.ToString(tbId.Text), dateBirth, tbName.Text, dateLast1);
            admin.Add(animal);
        }
        if (animalTypeComboBox.SelectedItem == "Cat")
        {
            SimpleDate dateBirth = new SimpleDate(ttbdateBirth.Value.Day, ttbdateBirth.Value.Month, ttbdateBirth.Value.Year);
            Animal animal = new Cat(Convert.ToString(tbId.Text), dateBirth, tbName.Text, tbBad.Text);
            admin.Add(animal);
        }
    }
}

After this is created I send this to an administration class which is suposed to add this dog or cat to an animal list however as mentioned in the title I get the NullReference error. The class that is supposed to add the cat or dog is as follows:

class Administration
{
    private List<Animal> animals;
    public List<Animal> Animals { get { return new List<Animal>(animals); } }

    public Administration ()
    {
        animals = new List<Animal>();
    }

    public bool Add(Animal animal)
    { 
        foreach (Animal dog in animals)
    {
            if(animal.ChipRegistrationNumber == dog.ChipRegistrationNumber)
            {
                MessageBox.Show("dog already added");
                break;
            }
    }
        foreach (Animal cat in animals)
        {
            if(animal.ChipRegistrationNumber == cat.ChipRegistrationNumber)
            {
                MessageBox.Show("dog already added");
                break;
            }
        }
        return true;
    }
}

Now my question is what am I doing wrong and how could I fix this so that I am able to add a cat or dog to the list.

Your variable `admin` doesn't seem to be instantiated ever. Is it? — Tristan McPherson, Oct 05 '14 at 17:22

score 2 · Accepted Answer · answered Oct 05 '14 at 17:28

2

Please let us know your error message such as which line it is complaining about. Plus you could try to initialize the admin.

public AdministrationForm()
{
    InitializeComponent();
    animalTypeComboBox.SelectedIndex = 0;
    animal = null;
    admin= new Administration();
}

answered Oct 05 '14 at 17:28

Hai Bi

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21

Thanks i indeed forgot to initialize the admin when i initialize the program no longer gives me the error – Damhuis Oct 05 '14 at 17:31

Adding a animal/dog/cat to a animal list results in NullReferenceException?

1 Answers1