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]]

* "Don" <un*****@oblivi on.com> scripsit:

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:

That's not possible with VB.NET.

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

[Jay B. Harlow [MVP - Outlook]]

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 normally reserve "Macro substitution" for the ability replace text
dynamically during C++ compilation. A feature that VB.NET does not support.
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? 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:
Const FORM_NAME_1 as String = "frmThisFor m"
Const FORM_NAME_2 as String = "frmThatFor m" Dim frmTemp As Form If condition then Dim typeForm As Type = Type.GetType(FO RM_NAME_1)
Dim value As Object = Activator.Creat eInstance(typeF orm)
frmTemp = DirectCast(valu e, Form) else
Dim typeForm As Type = Type.GetType(FO RM_NAME_2)
Dim value As Object = Activator.Creat eInstance(typeF orm)
frmTemp = DirectCast(valu e, Form) end if
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" <un*****@oblivi on.com> wrote in message
news:6YaYb.5317 65$X%5.223861@p d7tw2no... 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]]

Addendum:

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:

That's not possible with VB.NET.

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]

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