Calling InvokeMember on a Structure object does not update its value

[adiel_g@hotmail.com]

I am trying to set a value on a structure object dynamically using
InvokeMember. After I call InvokeMember, the value on the Admin flag
does not get updated. Here is the following sample code to reproduce
the behavior:

Public Class clsTest

Public Structure userGroupStruc
Dim User As Boolean ' User Account
Dim Admin As Boolean ' Administration Account
End Structure

Public objUserGroup As userGroupStruc

Public Sub setupAccess()

Dim currentGroup As String
currentGroup = "Admin" ' For the test, lets set Admin to
True

objUserGroup.Ge tType().InvokeM ember(currentGr oup,
Reflection.Bind ingFlags.SetFie ld, Nothing, objUserGroup, New Object()
{True})

End Sub

End Class


To test the behavior, simple create the class and call the setupAccess
method:
Dim objTest As New clsTest
objTest.setupAc cess()

If you then take a look at the value of objUserGroup.Ad min, it is
still false! (Even though we called InvokeMember and set it to true.)
I must be setting up the InvokeMember wrong but have been breaking my
head on this one... I would appreciate your help on this one.

Thanks Before Hand,
Adiel

[Armin Zingler]

Re: Calling InvokeMember on a Structure object does not update its value

<adiel_g@hotmai l.comschrieb

I am trying to set a value on a structure object dynamically using
InvokeMember. After I call InvokeMember, the value on the Admin
flag does not get updated. Here is the following sample code to
reproduce the behavior:

A structure is a value type. If you pass the object to InvokeMember, you
pass a copy of the object because the argument is passed ByVal. InvokeMember
would change the field value of the copy, but you never get the copy back.
The bottom line is: It does not work with value types.

Found this: (don't know if it helps or should be done)

http://mmarinov.blogspot.com/2007/01/reflection-modify-value-types-by.html

Armin

[adiel_g@hotmail.com]

Re: Calling InvokeMember on a Structure object does not update itsvalue

Thank You Armin, you have answered my question. I will take a look at
that article.

Adiel

[adiel_g@hotmail.com]

Re: Calling InvokeMember on a Structure object does not update itsvalue

I was able to resolve the problem by converting the structure into a
new class.

Thanks,
Adiel

[Herfried K. Wagner [MVP]]

Re: Calling InvokeMember on a Structure object does not update its value

<adiel_g@hotmai l.comschrieb:

>I am trying to set a value on a structure object dynamically using
InvokeMember. After I call InvokeMember, the value on the Admin flag
does not get updated. Here is the following sample code to reproduce
the behavior:
>
Public Class clsTest
>
Public Structure userGroupStruc
Dim User As Boolean ' User Account
Dim Admin As Boolean ' Administration Account
End Structure
>
Public objUserGroup As userGroupStruc
>
Public Sub setupAccess()
>
Dim currentGroup As String
currentGroup = "Admin" ' For the test, lets set Admin to
True
>
objUserGroup.Ge tType().InvokeM ember(currentGr oup,
Reflection.Bind ingFlags.SetFie ld, Nothing, objUserGroup, New Object()
{True})
>
End Sub
>
End Class
>[...]
If you then take a look at the value of objUserGroup.Ad min, it is
still false!

Sample for 'SetValue', which can be easily adapted to be used with
'InvokeMember':

\\\
Dim o As <structure type>
Dim x As ValueType = o
GetType(...).Ge tField(...).Set Value(x, <value>)
o = CType(x, <structure type>)
///

--
M S Herfried K. Wagner
M V P <URL:http://dotnet.mvps.org/>
V B <URL:http://dotnet.mvps.org/dotnet/faqs/>