Pulling data objects from a collection of various data types stored

25 Oct 2006 1:03 PM

kevinwolfe

Hello all,

I have a class which inherits 'Collection' and I use this class to
store different data types. I'd like to have a method inside the class
that does the following:

        For Each obj As Object In new_linked_collection
                Me.DoSomething(obj)
        Next

where DoSomething is overloaded for each of the different data types
I'm storing in the collection. The problem is, as I've defined obj as
an Object, visual basic craps a brick unless I recast obj to a
particlar type, such as

        For Each obj As Object In new_linked_collection
            If (obj.GetType.ToString.Equals("MyProgram.MyDataType1"))
Then
                Dim castedObj As MyDataType1 = obj
                Me.DoSomething(castedObj)
            Else
                Dim castedObj As MyDataType2 = obj
                Me.DoSomething(castedObj)
            End If
        Next

There has to be a more elegate way of doing this (expecially as I have
more than 2 different data types stored in the collection). Any
suggestions?

Thanks a bunch,

Kevin

26 Oct 2006 5:18 PM

Patrick Steele

In article <1161781409.449590.120***@i3g2000cwc.googlegroups.com>,
kevinwo***@gmail.com says...
Show quoteHide quote

> Hello all,
>
> I have a class which inherits 'Collection' and I use this class to
> store different data types. I'd like to have a method inside the class
> that does the following:
>
>         For Each obj As Object In new_linked_collection
>                 Me.DoSomething(obj)
>         Next
>
> where DoSomething is overloaded for each of the different data types
> I'm storing in the collection. The problem is, as I've defined obj as
> an Object, visual basic craps a brick unless I recast obj to a
> particlar type, such as
>
>         For Each obj As Object In new_linked_collection
>             If (obj.GetType.ToString.Equals("MyProgram.MyDataType1"))
> Then
>                 Dim castedObj As MyDataType1 = obj
>                 Me.DoSomething(castedObj)
>             Else
>                 Dim castedObj As MyDataType2 = obj
>                 Me.DoSomething(castedObj)
>             End If
>         Next
>
> There has to be a more elegate way of doing this (expecially as I have
> more than 2 different data types stored in the collection). Any
> suggestions?

One idea is to use interfaces. Create an interface with a method called
DoSomething:

Public Interface IWorker
    Sub DoSomething()
End Interface

Have each of the "types" of objects you're storing in the collection
implement the interface. Then just:

for each obj as IWork in new_linked_collection
    obj.DoSomething()
next

Another idea is to change the type of parameter DoSomething receives to
be an object and then use TypeOf to see what type is passed in:

public sub DoSomething(o as object)
    if typeof(o) is MyDataType1
        dim dt1 As MyDataType1 = DirectCast(o, MyDataType1)
        ' use dt1
    end if

    if typeof(o) is MyDataType2
        dim dt2 As MyDataType2 = DirectCast(o, MyDataType2)
        ' use dt2
    end if
end if

--
Patrick Steele
http://weblogs.asp.net/psteele