[RESOLVED] Overriding Hashtable's Item(KEY) Property

[wrack]

Hi,

I am using a Hashtable which stores unique names and objects associated with those names.

Now those objects have a property called "IsDynamic" and some of them have it set to false whie some of them have it set to true.

So when I retrieve any object using the key property, it goes to find me that object. How do I override that find method?

        Dim pTest As Hashtable

        pTest = New Hashtable

        pTest.Add("Test1", "Blah1")
        pTest.Add("Test2", "Blah2")
        pTest.Add("Test3", "Blah3")

        Dim sTest As String
        sTest = pTest("Test2")

I want to override the method which does this part

pTest("Test2")

so I can check certain things of the object first and if needed then call a method of that object before giving that object back to the user.

Hope this makes sense. If any questions then please ask. I am ok to create my object inheriting from Hashtable too.

Cheers

[jmcilhinney]

You shouldn't really be using a Hashtable at all in VB 2008. For standard work you should use a generic Dictionary. For custom work, there are various base classes in System.Collections and its child namespaces that provide various functionality you can inherit and extend.

[wrack]

Thanks Jim.

This is an old piece of code that I am trying to modify and was written in VS.NET 2003. For the moment I am stuck with it.

[wrack]

A more better and working code for more help.

Public Class FormMain

    Private Sub FormMain_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Dim pTest As Manager

        pTest = New Manager

        MessageBox.Show(DirectCast(pTest.Test("Test1"), MyObject).IsDynamic.ToString())
        MessageBox.Show(DirectCast(pTest.Test("Test2"), MyObject).IsDynamic.ToString())
        MessageBox.Show(DirectCast(pTest.Test("Test3"), MyObject).IsDynamic.ToString())

        ' What I want to do is anytime when pTest.Test("KEY-NAME") is called, it checks if the object's IsDynamic is set to True, if so, it calls the object's RefreshData method before giving the object back
    End Sub

End Class

Public Class Manager
    Private FTest As Hashtable

    Public ReadOnly Property Test() As Hashtable
        Get
            Return FTest
        End Get
    End Property

    Public Sub New()
        FTest = New Hashtable

        Dim pMyObject As MyObject

        pMyObject = New MyObject(Me, "Test1", False)
        pMyObject = New MyObject(Me, "Test2", True)
        pMyObject = New MyObject(Me, "Test3", False)
    End Sub

    Friend Sub AddToList(ByVal AMyObject As MyObject)
        FTest.Add(AMyObject.Name, AMyObject)
    End Sub
End Class

Public Class MyObject
    Private FName As String
    Private FIsDynamic As Boolean

    Public ReadOnly Property IsDynamic() As Boolean
        Get
            Return FIsDynamic
        End Get
    End Property

    Public ReadOnly Property Name() As String
        Get
            Return FName
        End Get
    End Property

    Private Sub RefreshData()
        ' Do something here
    End Sub

    Public Sub New(ByVal AParent As Manager, ByVal AName As String, ByVal AIsDynamic As Boolean)
        FName = AName
        FIsDynamic = AIsDynamic

        AParent.AddToList(Me)
    End Sub
End Class

[jmcilhinney]

You can't override a member that isn't declared Overridable. You pretty much have two choices:

1. Create a wrapper class for your Hashtable with a property/method that gets an item, processes it and then returns it.
2. Inherit the Hashtable class and shadow the Item property.

Just note that, if you go for the second option, you MUST always use references of your own type. If you cast as type Hashtable, which you can do, then you'll be using the original Hashtable.Item property implementation again.

[wrack]

Thanks Jim. Could you give me a quick example of both solution so I can weigh them individually? I think I don't have a choice but to implement my own class inheriting from the Hashtable.

[wrack]

Jim,

Never mind. I have restructured the code to avoid this whole thing. Refractoring is the king here! Thanks for the help and a valuable suggestion.

Cheers,
WRACK