.Contains on a list of custom class objects

Question

Hello,

I'm trying to use the .Contains function on a list of custom objects

This is the list:

List<CartProduct> CartProducts = new List<CartProduct>();

And the CartProduct:

public class CartProduct
{
    public Int32 ID;
    public String Name;
    public Int32 Number;
    public Decimal CurrentPrice;
    /// <summary>
    /// 
    /// </summary>
    /// <param name="ID">The ID of the product</param>
    /// <param name="Name">The name of the product</param>
    /// <param name="Number">The total number of that product</param>
    /// <param name="CurrentPrice">The currentprice for the product (1 piece)</param>
    public CartProduct(Int32 ID, String Name, Int32 Number, Decimal CurrentPrice)
    {
        this.ID = ID;
        this.Name = Name;
        this.Number = Number;
        this.CurrentPrice = CurrentPrice;
    }
    public String ToString()
    {
        return Name;
    }
}

So i try to find a similar cartproduct within the list:

if (CartProducts.Contains(p))

But it ignores similar cartproducts and i don't seem to know what it checks on - the ID? or it all?

Thanks in advance! :)

Answer 1

By default reference types have reference equality (i.e. two instances are only equal if they are the same object).

You need to override Object.Equals (and Object.GetHashCode to match) to implement your own equality. (And it is then good practice to implement an equality, ==, operator.)

Answer 2

If you want to have control over this you need to implement the [IEquatable interface][1]

[1]: http://This method determines equality by using the default equality comparer, as defined by the object's implementation of the IEquatable.Equals method for T (the type of values in the list).

Answer 3

You need to implement IEquatable or override Equals() and GetHashCode()

For example:

public class CartProduct : IEquatable<CartProduct>
{
    public Int32 ID;
    public String Name;
    public Int32 Number;
    public Decimal CurrentPrice;

    public CartProduct(Int32 ID, String Name, Int32 Number, Decimal CurrentPrice)
    {
        this.ID = ID;
        this.Name = Name;
        this.Number = Number;
        this.CurrentPrice = CurrentPrice;
    }

    public String ToString()
    {
        return Name;
    }

    public bool Equals( CartProduct other )
    {
        // Would still want to check for null etc. first.
        return this.ID == other.ID && 
               this.Name == other.Name && 
               this.Number == other.Number && 
               this.CurrentPrice == other.CurrentPrice;
    }
}

Answer 4

It checks to see whether the specific object is contained in the list.

You might be better using the Find method on the list.

Here's an example

List<CartProduct> lst = new List<CartProduct>();

CartProduct objBeer;
objBeer = lst.Find(x => (x.Name == "Beer"));

Hope that helps

You should also look at LinQ - overkill for this perhaps, but a useful tool nonetheless...

Answer 5

If you are using .NET 3.5 you can use LINQ extension methods to achieve a "contains" check with the Any extension method:

if(CartProducts.Any(prod => prod.ID == p.ID))

This will check for the existence of a product within CartProducts which has an ID matching the ID of p. You can put any boolean expression after the => to perform the check on.