Override .NET Generic List<MyType>.Contains(MyTypeInstance)?

Question

Is it possible, and if so how do I override the Contains method of an otherwise normal List<T>, where T is my own, custom type?

Answer 1

You need to override Equals and GetHashCode in your class (MyType).

Answer 2

If you implement the equals of you custom type, the contains function of List will work

Answer 3

To make your own Contains implementation you could create a class that implements the IList interface. That way your class will look like a IList. You could have a real List internally to do the standard stuff.

class MyTypeList : IList<MyType>
{
    private List<MyType> internalList = new ...;

    public bool Contains(MyType instance)
    {

    }

    ....
}

Answer 4

List<T> uses EqualityComparer<T>.Default to do comparisons; this checks first to see if your object implements IEquatable<T>; otherwise is uses object.Equals.

So; the easiest thing to do is to override Equals (always update GetHashCode to match the logic in Equals). Alternatively, use LINQ instead:

bool hasValue = list.Any(x => x.Foo == someValue);

Answer 5

Depending on what specific needs you have in your override you might use Linq expression for doing that:

list.Any(x => x.Name.Equals("asdas", .....)) // whatever comparison you need

You can then wrap it in an extension method for convenience.