C＃Dictionary.ContainsKey（）始终返回false

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);
    }
}

Answer 2

You need to override GetHashCode() :

http://msdn.microsoft.com/en-us/library/ms182358(v=vs.80).aspx

GetHashCode returns a value based on the current instance that is suited for hashing algorithms and data structures such as a hash table. Two objects that are the same type and are equal must return the same hash code to ensure that instances of System.Collections.HashTable and System.Collections.Generic.Dictionary work correctly.

Answer 3

I know this question already have an accepted answer but i'll share my dirty solution too.

Boolean found = 
   dict.Keys.Any(key => 
                 key.Equals("key", StringComparison.InvariantCultureIgnoreCase));