Collection .Contains() not working

I've check everywhere and can't find a solution. I have the following

Dim users as New List(of TUser)

Private Sub AddSelectedUsers()

For Eac开发者_JAVA技巧h user as TUser in gridSelectedItems()

If Not users.Contains(user) Then

users.Add(user)

End If

Next

End Sub 

The "Contains" is not working. I keep getting duplicates on the users list.

The List.Contains() method uses the default equality operator. Since TUser appears to be a class, List.Contains() will only match if you are referencing the exact same instance of TUser in both comparisons, apparently isn't the case. See a more detailed explanation here.

The solution is to implement an equality override for the TUser class, as per the example here.