Question

In VB6, there used to be a Collection data type that would allow retrieval of an item in the collection by either its key or its ordinal. However, it wasn’t strongly typed.

Now, with VB.Net, I am looking for a suitable replacement that is strongly type and could be used with a generic collection.

This is a simple example of what I want to do. The only problem is that the underlying collection class, BindingList, does not support efficient retrieval of an item by an alpha key, so I have to loop through the elements to get the item I am looking for. For large collections, this is not efficient.

I have looked though the various Collection type classes and have found no suitable replacement.

This is what I want to do, except for the looping that is done with the Item property.

Rather than just saying “Use Hash tables” or something like that, if you could, please include the detailed out as I have done for the short example below.

Public Class Car

    Public Sub New(ByVal keyName As String, ByVal property1 As String)
        _KeyName = keyName
        _Property1 = property1
    End Sub

    Dim _KeyName As String

    Public Property KeyName() As String
        Get
            Return _KeyName
        End Get
        Set(ByVal value As String)
            _KeyName = value
        End Set
    End Property

    Public _Property1 As String

    Public Property Property1() As String
        Get
            Return _Property1
        End Get
        Set(ByVal value As String)
            _Property1 = value
        End Set
    End Property

End Class

Public Class Cars

    Inherits System.ComponentModel.BindingList(Of Car)

    Public Overloads ReadOnly Property Item(ByVal key As String) As Car
        Get
            For Each CurrentCar As Car In Me.Items
                If CurrentCar.KeyName = key Then
                    Return CurrentCar
                End If
            Next
            Return Nothing
        End Get
    End Property

End Class

Answer 1

I believe you’re looking for Dictionary<TKey, TValue>. In fact, if you do want your own collection class that’s strongly typed and isn’t (itself) generic, if you change your parent class to Dictionary<string, Car>, you should be all set. This all does, of course, assume that you add the cars to the collection with an explicit string key. If you want the lookup to be based on the value of a property in the collection, you’d do better either using or inheriting from List<Car> and using LINQ to query the list. You could then have…

Public Overloads ReadOnly Property Item(ByVal key As String) As Car
    Get
        Return (from c in Me where c.KeyName = key select c).SingleOrDefault()
    End Get
End Property