Macro Substitution?

[Don]

I think "macro substitution" is the correct term for what I want to do, but,
to be sure, here is a description of what I'd like to know is possible:

I want to be able to create a create an object of a type whose name is
stored in a constant. For example:


Const FORM_NAME_1 as String = "frmThisFor m"
Const FORM_NAME_2 as String = "frmThatFor m"

Dim frmTemp as Form


If condition then
frmTemp = CType(frmTemp, FORM_NAME_1)
frmTemp = New FORM_NAME_1
else
frmTemp = CType(frmTemp, FORM_NAME_2)
frmTemp = New FORM_NAME_2
end if

frmTemp.Show

etc....


In the pseudo code above, I want to somehow access the string stored in
FORM_NAME_1 and FORM_NAME_2 in the lines of code where I use CType and New.
Is it possible to even do this in VB.NET?

- Don

[Herfried K. Wagner [MVP]]

Re: Macro Substitution?

* "Don" <unknown@oblivi on.com> scripsit:[color=blue]
> I think "macro substitution" is the correct term for what I want to do, but,
> to be sure, here is a description of what I'd like to know is possible:
>
> I want to be able to create a create an object of a type whose name is
> stored in a constant. For example:[/color]

That's not possible with VB.NET.

--
Herfried K. Wagner [MVP]
<http://www.mvps.org/dotnet>

[Jay B. Harlow [MVP - Outlook]]

Re: Macro Substitution?

Don,[color=blue]
> I think "macro substitution" is the correct term for what I want to do,[/color]
but,[color=blue]
> to be sure, here is a description of what I'd like to know is possible:[/color]
I normally reserve "Macro substitution" for the ability replace text
dynamically during C++ compilation. A feature that VB.NET does not support.
[color=blue]
> In the pseudo code above, I want to somehow access the string stored in
> FORM_NAME_1 and FORM_NAME_2 in the lines of code where I use CType and[/color]
New.[color=blue]
> Is it possible to even do this in VB.NET?[/color]
Not with CType & New.

Have a look at the System.Activato r.CreateInstanc e method, which allows you
to dynamically load & create an object based on a string.

Something like:
[color=blue]
> Const FORM_NAME_1 as String = "frmThisFor m"
> Const FORM_NAME_2 as String = "frmThatFor m"[/color]
Dim frmTemp As Form[color=blue]
> If condition then[/color]
Dim typeForm As Type = Type.GetType(FO RM_NAME_1)
Dim value As Object = Activator.Creat eInstance(typeF orm)
frmTemp = DirectCast(valu e, Form)[color=blue]
> else[/color]

Dim typeForm As Type = Type.GetType(FO RM_NAME_2)
Dim value As Object = Activator.Creat eInstance(typeF orm)
frmTemp = DirectCast(valu e, Form)[color=blue]
> end if[/color]

Note for Type.GetType to work above, "frmThisFor m" needs to be in the
current assembly. If "frmThisFor m" is not in the current assembly, then
FORM_NAME_1 needs to be in the "namespace.clas s, assembly" instead of simply
the "class" format.

Hope this helps
Jay

"Don" <unknown@oblivi on.com> wrote in message
news:6YaYb.5317 65$X%5.223861@p d7tw2no...[color=blue]
> I think "macro substitution" is the correct term for what I want to do,[/color]
but,[color=blue]
> to be sure, here is a description of what I'd like to know is possible:
>
> I want to be able to create a create an object of a type whose name is
> stored in a constant. For example:
>
>
> Const FORM_NAME_1 as String = "frmThisFor m"
> Const FORM_NAME_2 as String = "frmThatFor m"
>
> Dim frmTemp as Form
>
>
> If condition then
> frmTemp = CType(frmTemp, FORM_NAME_1)
> frmTemp = New FORM_NAME_1
> else
> frmTemp = CType(frmTemp, FORM_NAME_2)
> frmTemp = New FORM_NAME_2
> end if
>
> frmTemp.Show
>
> etc....
>
>
> In the pseudo code above, I want to somehow access the string stored in
> FORM_NAME_1 and FORM_NAME_2 in the lines of code where I use CType and[/color]
New.[color=blue]
> Is it possible to even do this in VB.NET?
>
> - Don
>
>[/color]

[Herfried K. Wagner [MVP]]

Re: Macro Substitution?

Addendum:
[color=blue][color=green]
>> I think "macro substitution" is the correct term for what I want to do, but,
>> to be sure, here is a description of what I'd like to know is possible:
>>
>> I want to be able to create a create an object of a type whose name is
>> stored in a constant. For example:[/color]
>
> That's not possible with VB.NET.[/color]

I pressed "Send" before completing my reply...

<http://www.google.de/groups?selm=bum k7n%24j9mbf%241 %40ID-208219.news.uni-berlin.de>

--
Herfried K. Wagner [MVP]
<http://www.mvps.org/dotnet>

[Don]

Re: Macro Substitution?

I figured out how to do what I wanted:


Private Sub MacroSubstution Example(ByVal blnUseClass1 as Boolean)

' These are constants containing the names of my classes (the names must
include the namespace)
Const CLASS_NAME_1 as String = "MyNameSpace.My ClassName1"
Const CLASS_NAME_2 as String = "MyNameSpace.My ClassName2"

Dim strType As String ' I'll throw the name of the class I want in
here.
Dim obj As clsBase ' This is the object with which I will be
instantiation either MyClassName1 or MyClassName1
' NOTE: In my example, clsBase is the parent
class of MyClassName1 and MyClassName1. Using
' Dim obj As Object would work just as well.

Try

' Determine which class I should instantiate
If blnUseClass1 Then
strType = CLASS_NAME_1
Else
strType = CLASS_NAME_2
End If

' Create new object of the type that we want (** This is it!!! **)
obj = Activator.Creat eInstance(Type. GetType(strType ))

' Show a message which displays the type of the object I just
instantiated
MsgBox(TypeName (obj))

' Clean up
obj = Nothing

Catch ex As Exception

' Display error message
MsgBox(ex.Messa ge)

End Try

End Sub


This worked for me. Thanks for the tips, guys!

- Don