Generic Collections - vb.net

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

Answer 2

Do you really need both access by key AND index?
If you do not, then use a Dictionary(Of String, Car), and use
- MyCol.Items("XXX") to retrieve an item by key (or the shorthand MyCol("XXX"))
- MyCol.ContainsKey("XXX") to test if a key exists in the collection
- For Each Entry as KeyValuePair(Of String, Car) in MyCol if you want to enumerate all objects AND their key
- For Each Entry as Car in MyCol.Values if you want to enumerate the entries without consideration for the key
If you need both access by index and key, I'm afraid your best bet is to use a List(of Car) and a Dictionary(of Car) rolled into one custom collection class, because I believe they went away from that kind of collection which is not really all that useful for most problems.

Answer 3

This is what I am thinking is my best solution. I welcome comments for a better way!
Imports Microsoft.VisualBasic
Public Class Car
Implements Xs(Of Car).IKeyName
Private _KeyName As String
Public Sub New(ByVal keyName As String, ByVal property1 As String)
_KeyName = keyName
_Property1 = property1
End Sub
Public Property KeyName() As String Implements Xs(Of Car).IKeyName.KeyName
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
Public Class X
Private _KeyName As String
Public Property KeyName() As String
Get
Return _Keyname
End Get
Set(ByVal value As String)
_Keyname = value
End Set
End Property
End Class
Public Class Xs(Of X)
Inherits Hashtable
Interface IKeyName
Property KeyName() As String
End Interface
Public Shadows Sub Add(ByVal item As IKeyName)
MyBase.Add(item.KeyName, item)
End Sub
Public Shadows ReadOnly Property Item(ByVal key As String) As x
Get
If Me.ContainsKey(key) Then
Return MyBase.Item(key)
Else
'If I mispell a key, I don't want to end up creating a new mispelled version, I want an error
Throw New Exception("Element with key " & key & " is not found")
End If
End Get
End Property
End Class
Public Class Cars2
Inherits Xs(Of Car)
End Class
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
Dim MyCar As New Car("key1", "prop1")
'First approach
Dim MyCars As New Cars
MyCars.Add(MyCar)
Dim RetrievedCar As Car = MyCars.Item("key1") 'Inefficient retrieval by key (uses looping)
'Second approach
Dim Cars2 As New Cars2
Cars2.Add(MyCar)
Dim RetrievedCar2 As Car = Cars2.Item("key1") 'Can now efficiently retreive an item by its key
End Sub

Answer 4

The OrderedDictionary in the System.Collections.Specialized namespace can be accessed by index and by key, if you ever need that. But looking at your solution, it looks like a standard Dictionary, but less efficient because it forces a string type for keys.
Is there any reason you can't use the Dictionary .NET provides you, or another collection type that's already in .NET like OrderedDictionary?