Generic Class: Passing Data Type to Placeholder

[Etienne-Louis Nicolet]

I have a generic class defined as follows:

Public Class SqlArgument(Of TDataType)

Private _values as List(Of TDataType)

Public Property Values() As List(Of TDataType)
Get
Return _values
End Get
Set(ByVal pValues As List(Of TDataType))
_values = pValues
End Set

Public Sub New()
Me.Values = New List(Of TDataType)
End Sub

....

End Class
Given the DataType property of a (strongly typed) DataTable I'd like to
create a new instance of SqlArgument with the data type of the appropriate
table column. I thought about something like

Sub TestArgument(pColumn as System.Data.DataColumn)
...
Dim s As new SqlArgument(Of pColumn.DataType)
...
End Sub

but obviously this does not work. Can anybody give me a hint on how to do
this?

Many thanks for your suggestions,
Etienne

[Mattias Sjögren]

>Given the DataType property of a (strongly typed) DataTable I'd like to

>create a new instance of SqlArgument with the data type of the appropriate
table column. I thought about something like

Sub TestArgument(pColumn as System.Data.DataColumn)
...
Dim s As new SqlArgument(Of pColumn.DataType)
...
End Sub

but obviously this does not work. Can anybody give me a hint on how to do
this?

You have to go the Reflection route if you want to do this. You can
instantiate the right generic type using Type.MakeGenericType and then
an object from that type with Activator.CreateInstance. But know that
once you've started using Reflection, it's hard to do something
without it, and the code quickly gets pretty ugly.

What are you actually going to do with the s variable once you've
created the instance?
Mattias

--
Mattias Sjögren [C# MVP] mattias @ mvps.org
http://www.msjogren.net/dotnet/ | http://www.dotnetinterop.com
Please reply only to the newsgroup.

[Marc Gravell]

Can I just say: look at LINQ-to-SQL; that is exactly what it does for
you. You might be able to save a lot of effort...

Marc

[Etienne-Louis Nicolet]

Dear Marc,

I bought a book on LINQ yesterday and will have a look at it. Thanks for the
tip!

Kind regards,
Etienne

"Marc Gravell" <ma**********@gmail.comwrote in message
news:%2******************@TK2MSFTNGP05.phx.gbl...

Can I just say: look at LINQ-to-SQL; that is exactly what it does for you.
You might be able to save a lot of effort...

Marc

[Etienne-Louis Nicolet]

"Mattias Sjögren" <ma********************@mvps.orgwrote in message
news:ef****************@TK2MSFTNGP03.phx.gbl...

Given the DataType property of a (strongly typed) DataTable I'd like to
create a new instance of SqlArgument with the data type of the appropriate
table column. I thought about something like

Sub TestArgument(pColumn as System.Data.DataColumn)
...
Dim s As new SqlArgument(Of pColumn.DataType)
...
End Sub

but obviously this does not work. Can anybody give me a hint on how to do
this?

You have to go the Reflection route if you want to do this. You can
instantiate the right generic type using Type.MakeGenericType and then
an object from that type with Activator.CreateInstance. But know that
once you've started using Reflection, it's hard to do something
without it, and the code quickly gets pretty ugly.

What are you actually going to do with the s variable once you've
created the instance?
Mattias

--
Mattias Sjögren [C# MVP] mattias @ mvps.org
http://www.msjogren.net/dotnet/ | http://www.dotnetinterop.com
Please reply only to the newsgroup.

Dear Mattias,

I tried to figure out how to use Reflection as recommended. I think i got
the first part:

Sub TestArgument(pColumn as System.Data.DataColumn)
Dim generic As System.Type = GetType(SqlArgument(Of ))
Dim typeArgs() As Type = {pColumn.DataType}
Dim constructed As Type = generic.MakeGenericType(typeArgs)
....
End Sub
However, I did not get along with the VB help on Activator.CreateInstance.
Would you mind giving me a hint how the code should look like?

Many thanks & kind regards,
Etienne