[RESOLVED] Passing a Type as an argument...

[JohnnyD]

Hi,

I'm using VB.NET 2003 with .NET Framework v1.1. I know it's getting a bit old now but I'm stuck with an existing program and don't have the time/knowhow to convert it to anything newer.

My question would probably be solved very easily with Generics in .NET 2.0 but as I can't use that right now, I'd like to know if the following is possible:

I have a load of manager classes which inherit from DictionaryBase and hold collections of my custom classes. For example, I have a Employee class, a Batch class, a Supplier class, etc... and each of these has a Manager classwhich holds a collection of them - eg: my PlantTrayMgr class holds collections of PlantTrays, etc..

I have one particular form where I have to populate loads of comboboxes with the contents of various Manager objects. What I currently do in my form load event to populate comboboxes is this:

Option Strict On
Option Explicit On

Private _plantTrayMgr As PlantTrayMgr

Private Sub frmPlantEdit_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles MyBase.Load

        Dim dictEntry As DictionaryEntry

        _plantTrayMgr = PlantTrayMgr.GetInstance

        uxTrayType.Items.Clear()        'uxTrayType is the comboBox which lists the tray types.

        For Each dictEntry In _plantTrayMgr             ' the enumerator of a dictionary returns a 
                                                        ' DictionaryEntry object which has to be
                                                        ' converted to the correct type before being
                                                        ' added to the combobox

            Dim pt As PlantTray = CType(dictEntry.Value, PlantTray)

            uxTrayType.Items.Add(pt)
        Next

End Sub

But I have so many comboboxes to fill I thought there must be an easier way. I wanted to add a method to my Manager classes called something like 'FillList' but to save having to type it out separately for every manager class, I was going to make a base class with this 'FillList' method in which all my manager classes could inherit from. like this:

Public MustInherit Class MgrBase
    Inherits System.Collections.DictionaryBase

    Public Sub FillList(ByVal listObject As IList, ByVal convertType As Type)

        Dim dictEntry As DictionaryEntry

        For Each dictEntry In Me.Dictionary
            listObject.Add(CType(dictEntry.Value, convertType))
        Next
    End Sub

End Class

And then I could do something like this from my forms:

        uxTrayType.Items.Clear()
        _plantTrayMgr.FillList(uxTrayType.Items, GetType(PlantTray))

but I get an error even before I compile the project saying "Type 'convertType' is not defined." which referrs to this line in the MgrBase class:

            listObject.Add(CType(dictEntry.Value, convertType))

Am I barking up the wrong tree and trying to do something which is impossible without Generics? Or do I need to override this new 'FillList' method in every single manager class in my project?

Any ideas very much appreciated.

John.

[dglienna]

Can't you BIND the combo box to the data?

[JohnnyD]

Can't you BIND the combo box to the data?

I hadn't thought of that but after a bit of investigating I think my manager classes would have to implement IList but, because they inherit from DictionaryBase, they don't.

I thought of adding the neccessary code to implement IList but because it is inherently a dictionary, it doesn't have an index as such so would be very hard to implement.

Unless there is an easy way?

[dglienna]

Convert them to tables?

[JohnnyD]

I think for the amount of hassle that would take, I'm better off just having an overloaded method in each of my manager classes.

Thanks for the suggestions though. Out of interest, am I right in thinking this kind of thing is what Generics is all about? I've read a little bit about it but not much..