Get object from name

5 Jul 2006 12:41 PM

Bert

Hi,

I need to identify an object from its name, something like this:

Class User
    dim Username as string
    property Name() as string
        get
            Return Username
        end Get
        Set(value as string)
            Username = value
        end Set
    end property
End Class

Class MyClass
     Friend User1 as new User
     Friend User2 as new User

    Sub Main
        User1.Username = "Bill"
        User2.Username = "George"
    end sub

    Function GetUsername(strUser as string) as String
        dim oUser as Object
        oUser = GetObjectFromName(strUser)
        return oUser.Username
    end Function

    Function GetObjectFromName(strName as string) as Object
        ???????
        ???????
    End Function
End Class

Anyone knows how this function "GetObjectFromName" would look like?
(Btw, the object could be an instance of any Class, this is just a simplified example)

Thanks,
Egbert

5 Jul 2006 1:12 PM

Jim Wooley

Perhaps the following will assist.

Public Shared Function CreateObjectByStringName(ByRef sObjectName As String,
Optional ByRef sAssemblyFile As String = "") As Object
        Try
            If sAssemblyFile = "" Then
                Return (System.Activator.CreateInstance(System.Type.GetType(sObjectName)))
            Else
                Return Activator.CreateInstanceFrom(sAssemblyFile, sObjectName).Unwrap()
            End If
        Catch ex As Exception
            Throw New System.IO.FileNotFoundException("Unable to locate resource:
" & sAssemblyFile & "." & sObjectName, ex)
        End Try
End Function
Jim Wooley
http://devauthority.com/blogs/jwooley/default.aspx

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> Hi,
>
> I need to identify an object from its name, something like this:
>
> Class User
> dim Username as string
> property Name() as string
> get
> Return Username
> end Get
> Set(value as string)
> Username = value
> end Set
> end property
> End Class
> Class MyClass
> Friend User1 as new User
> Friend User2 as new User
> Sub Main
> User1.Username = "Bill"
> User2.Username = "George"
> end sub
> Function GetUsername(strUser as string) as String
> dim oUser as Object
> oUser = GetObjectFromName(strUser)
> return oUser.Username
> end Function
> Function GetObjectFromName(strName as string) as Object
> ???????
> ???????
> End Function
> End Class
> Anyone knows how this function "GetObjectFromName" would look like?
> (Btw, the object could be an instance of any Class, this is just a
> simplified example)
>
> Thanks,
> Egbert

5 Jul 2006 1:39 PM

Bert

Jim, thanks for your help, but this is not wat I am looking for. Your function returns a new instance of the class "sObjectName".
So sObjectName should be a Class name like "myNamespace.User", and not "User1".

What I want to do is to make a "copy" of an object like:
dim NewObject as Object = User1
but then:
dim NewObject as Object = GetObjectFromName("User1")

I am not sure if this is possible at all !!
Egbert

Show quoteHide quote

"Jim Wooley" <jimNOSPAMwooley@hotmail.com> wrote in message news:24f81e8f4b098c86e2a36cb00ad@msnews.microsoft.com...
> Perhaps the following will assist.
>
> Public Shared Function CreateObjectByStringName(ByRef sObjectName As String,
> Optional ByRef sAssemblyFile As String = "") As Object
>        Try
>            If sAssemblyFile = "" Then
>                Return (System.Activator.CreateInstance(System.Type.GetType(sObjectName)))
>            Else
>                Return Activator.CreateInstanceFrom(sAssemblyFile, sObjectName).Unwrap()
>            End If
>        Catch ex As Exception
>            Throw New System.IO.FileNotFoundException("Unable to locate resource:
> " & sAssemblyFile & "." & sObjectName, ex)
>        End Try
> End Function
> Jim Wooley
> http://devauthority.com/blogs/jwooley/default.aspx
>
>> Hi,
>>
>> I need to identify an object from its name, something like this:
>>
>> Class User
>> dim Username as string
>> property Name() as string
>> get
>> Return Username
>> end Get
>> Set(value as string)
>> Username = value
>> end Set
>> end property
>> End Class
>> Class MyClass
>> Friend User1 as new User
>> Friend User2 as new User
>> Sub Main
>> User1.Username = "Bill"
>> User2.Username = "George"
>> end sub
>> Function GetUsername(strUser as string) as String
>> dim oUser as Object
>> oUser = GetObjectFromName(strUser)
>> return oUser.Username
>> end Function
>> Function GetObjectFromName(strName as string) as Object
>> ???????
>> ???????
>> End Function
>> End Class
>> Anyone knows how this function "GetObjectFromName" would look like?
>> (Btw, the object could be an instance of any Class, this is just a
>> simplified example)
>>
>> Thanks,
>> Egbert
>
>

5 Jul 2006 1:34 PM

Andrew Morton

Can't you just store the user objects in a Dictionary so that you can access
them directly by name?

Andrew

5 Jul 2006 2:10 PM

Phill W.

Bert wrote:

> I need to identify an object from its name

If you want to identify an instance of an object by a given key, use one
of the Collection classes within the Framework - HashTable would be ideal.

Class MyClass
    Private m_oTable As New HashTable
    Sub Main()
       Dim oNewUser As New User( "Bill" )
       m_oTable.Add( "Bill", New User( "Bill" ) )
       m_oTable.Add( "George", New User( "George" ) )

       Console.Writeline( m_oTable.Item( "Bill" ).ToString() )
    End Sub
End Class

> Btw, the object could be an instance of any Class, this is just a simplified example

That's
(a) heading off into the land of Reflection, where you can find out just
about anything about any method or property and
(b) IMHO, probably not the best solution.

What is it you're actually trying to achieve?

Regards,
Phill W.

5 Jul 2006 2:39 PM

Bert

Phill,

> That's
> (a) heading off into the land of Reflection, where you can find out just
> about anything about any method or property and
> (b) IMHO, probably not the best solution.
>
> What is it you're actually trying to achieve?

The land of Reflection is a very fascinating land, and can be very, very usefull in creating dynamic and flexible solutions.

I'm just trying to avoid to keep up hashtables or dictionaries or so, although that solution will work in my case. What I want is to be able to invoke any member of any object at runtime based on input or database-data.

regards,
Egbert

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"Phill W." <p-.-a-.-w-a-r-d@o-p-e-n-.-a-c-.-u-k> wrote in message news:e8gh2g$aot$1@yarrow.open.ac.uk...
> Bert wrote:
>
>> I need to identify an object from its name
>
> If you want to identify an instance of an object by a given key, use one
> of the Collection classes within the Framework - HashTable would be ideal.
>
> Class MyClass
>    Private m_oTable As New HashTable
>    Sub Main()
>       Dim oNewUser As New User( "Bill" )
>       m_oTable.Add( "Bill", New User( "Bill" ) )
>       m_oTable.Add( "George", New User( "George" ) )
>
>       Console.Writeline( m_oTable.Item( "Bill" ).ToString() )
>    End Sub
> End Class
>
>> Btw, the object could be an instance of any Class, this is just a simplified example
>
> That's
> (a) heading off into the land of Reflection, where you can find out just
> about anything about any method or property and
> (b) IMHO, probably not the best solution.
>
> What is it you're actually trying to achieve?
>
> Regards,
>    Phill W.

6 Jul 2006 1:12 PM

Phill W.

Bert wrote:

> The land of Reflection is a very fascinating land, and can be very, very usefull in creating dynamic and flexible solutions.

Wholely agree with you, but would still emphasises the "/can be/" part
of the above.
Im my experience, a truly Reflection-based solution is oftem more
laborious than a more restrictive, but better-targeted approach.

> What I want is to be able to invoke any member of any object at runtime based on input or database-data.

Would you consider a kind of "command-line" interface into any of your
classes? This is an approach I've used recently:

Public Interface IControllable
Execute( ByVal sCommand as String ) as String
End Interface

Any class that I want to "drive" from my external source implements this
interface (the method is deliberately /over/-simplified because the
client-end is a TCP socket). Within the method's implementation,
though, I can make the object do anything that it can do internally.

Regards,
Phill W.