Question

I have a Dictionary and every time I call the ContainsKey method it returns false. Take the following example

 Boolean found = dict.ContainsKey(new Group("group1", "test"));

The found variable is false eventhough the visual studio debugger shows that a Group with the name “group1” and type “test” is present in dict. What is going on?

My Group class has two String fields (type and name) and I override the Equals method

public override bool Equals(object obj)
{
    Group otherGroup = (Group)obj;
    return this.name == otherGroup.name && this.type == otherGroup.type;
}

Answer 1

You should override GetHashCode method

An example of HashMethod for a class containing 2 string properties

public override int GetHashCode()
{
    unchecked
    {
        return ((name != null ? name.GetHashCode() : 0)*397) ^ (type != null ? type.GetHashCode() : 0);
    }
}