Shared functions vs Non-Shared Functions

[tshad]

I am setting up some of my functions in a class called MyFunctions.

I am not clear as to the best time to set a function as Shared and when not
to. For example, I have the following bit manipulation routines in my
Class:

*******************************************************************************
imports System

NameSpace MyFunctions

Public Class BitHandling

'*----------------------------------------------------------*
'* Name : BitSet *
'*----------------------------------------------------------*
'* Purpose : Sets a given Bit in Number *
'*----------------------------------------------------------*
Public Shared Function BitSet(Number As Integer, _
ByVal Bit As Integer) As Long
If Bit = 31 Then
Number = &H80000000 Or Number
Else
Number = (2 ^ Bit) Or Number
End If
BitSet = Number
End Function

'*----------------------------------------------------------*
'* Name : BitClear *
'*----------------------------------------------------------*
'* Purpose : Clears a given Bit in Number *
'*----------------------------------------------------------*
Public Shared Function BitClear(Number As Integer, _
ByVal Bit As Integer) As Long
If Bit = 31 Then
Number = &H7FFFFFFF And Number
Else
Number = ((2 ^ Bit) Xor &HFFFFFFFF) And Number
End If

BitClear = Number
End Function

'*----------------------------------------------------------*
'* Name : BitIsSet *
'*----------------------------------------------------------*
'* Purpose : Test if bit 0 to bit 31 is set *
'*----------------------------------------------------------*
Public Shared Function BitIsSet(ByVal Number As Integer, _
ByVal Bit As Integer) As Boolean
BitIsSet = False

If Bit = 31 Then
If Number And &H80000000 Then BitIsSet = True
Else
If Number And (2 ^ Bit) Then BitIsSet = True
End If
End Function

End Class

End Namespace

********************************************************************************

Now I have these set up as shared so I don't have to create an instance of
the class:

temp = BitHandling.BitSet(temp,3)

vs.

dim MyBits as new BitHandling
temp = MyBits.BitSet(temp,3)

I am also setting up my function to send out various emails which entails
reading an Sql Record and reading a text file from disk, as well as sending
the email:

SmtpMail.SmtpServer = mailServer
smtpMail.Send(message)

What would tell me that I need to make this a non-shared function vs a
shared one?

Thanks,

Tom

 

[Karl Seguin]

Tom:
Is the function manipulating instance data? Looking at your functions, they
look like they need to be shared.

Think of it this way.

You have a class called Car, which has a property named AirbagDeployed as
boolean

if you have a function named DeployAirbag() it would need to be an
instance (non-shared) method. Why? Because you would have create a new car
instance and would want to deploy that particular car's airbag. in other
words, instnace methods behave against a particular instance. Your
BitHandling class looks like a helper function for dealing with bit
information. You wouldn't create separate instance of them as you don't
need to represent different bithandling (as you would differnent
cars)...ergo your function don't behave against instances.

A case where you might have instances is if your BitHandling was
culture-specific. In which case you might have different bithandling
instances per culture. In this case you'd need to create a new BitHandling
class (specifying the culture) and then your functions would behave against
that particular instance. (As an aside, an alternative would be to pass the
culture information to each shared function so you wouldn't need to create
culture-specific instances which works fine for a single parameter, but
becomes messy when you're talking about more..)

Karl



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[tshad]

Tom:
Is the function manipulating instance data? Looking at your functions,
they look like they need to be shared.

Think of it this way.

You have a class called Car, which has a property named AirbagDeployed as
boolean

if you have a function named DeployAirbag() it would need to be an
instance (non-shared) method. Why? Because you would have create a new
car instance and would want to deploy that particular car's airbag. in
other words, instnace methods behave against a particular instance. Your
BitHandling class looks like a helper function for dealing with bit
information. You wouldn't create separate instance of them as you don't
need to represent different bithandling (as you would differnent
cars)...ergo your function don't behave against instances.

A case where you might have instances is if your BitHandling was
culture-specific. In which case you might have different bithandling
instances per culture. In this case you'd need to create a new
BitHandling class (specifying the culture) and then your functions would
behave against that particular instance. (As an aside, an alternative
would be to pass the culture information to each shared function so you
wouldn't need to create culture-specific instances which works fine for a
single parameter, but becomes messy when you're talking about more..)

That's what gets confusing. Trying to figure out the instances bit (no pun
intended) and if it is needed. Here is the other function that I am
creating to put in my MyFunctions Namespace. I would give is a class of
email, I suppose.

This is just my prototype email program that I am putting together to make a
more generalized function from.

It, in essence:
gets the connection to Sql
gets the email record to get the subject and from/to addresses
reads a text file to put into the body of the message
adds a few things to the email
sends the email

I would probably change the function to something like:

public shared sendEmail(filename as string, subject as string)

***************************************************************************************
sub sendEmail ( )
dim webMasterEmail As String
dim emailSubject As String
Dim mailServer As String
Dim contactEmail As String
Dim screenTestSubject As String

Dim emailReader As SqlDataReader

Dim ConnectionString as String
=System.Configuration.ConfigurationSettings.AppSettings("MM_CONNECTION_STRING_solutions")
Dim objConn as New SqlConnection (ConnectionString)
Dim CommandText as String = "Select
MailServer,WebMasterEmail,ContactEmail,ScreenTestSubject from emailResponse
where ClientID = '1234'"
Dim objCmd as New SqlCommand(CommandText,objConn)

objConn.Open()

emailReader = objCmd.ExecuteReader

if emailReader.Read then
mailServer = emailReader("MailServer")
webMasterEmail = emailReader("WebMasterEmail")
contactEmail = emailReader("ContactEmail")
screenTestSubject = emailReader("ScreenTestSubject")
end If

objConn.close()

dim URLPath As String = _
Left(request.path, InStrRev(request.path, "/") - 1)

Dim objStreamReader as StreamReader
Dim strInput As String
Dim strBuffer As String

If File.exists(MapPath("\new_account_automail.htm")) then
objStreamReader = File.OpenText(MapPath("\new_account_automail.htm"))
strInput = objStreamReader.ReadLine()
while strInput <> nothing
strBuffer = strBuffer & strInput
strInput = objStreamReader.ReadLine()
end while
objStreamReader.Close
end if

Dim Message As New MailMessage()
message.To = contactEmail
message.From = webMasterEmail
message.Subject = screenTestSubject
message.Body = "This is line 1<br><br>"
message.Body = message.Body & "This is line 2<br><br>"
strInput = strBuffer.replace("#MESSAGE#",message.Body)
strInput = strInput.replace("#MAILTITLE#","Screen Test Confirmation")
message.Body = strInput
message.BodyFormat = MailFormat.Html
SmtpMail.SmtpServer = mailServer
smtpMail.Send(message)
end sub
*****************************************************************************

Would this work as a shared function, or would I need to make this an
instance?

Thanks,

Tom

 

[Karl Seguin]

You would create an instance class with instance members if you wanted to
create an Email object, set it's properties and have a Send() method, ala:

dim email as new Email("some subject")
email.Body = "xxx"
email.Send()


you would use a shared member if you wanted to pass everything in as
parameters

EmailHelp.Send("some subject", "xxx")

I personally prefer the syntax of the 2nd example...but if you wanted to
keep a bunch of different emails, say you wanted to cache them or move them
around between your layers, it'd be necessary to have distinct instances.

Trust your gut feeling.

Karl

--
MY ASP.Net tutorials
http://www.openmymind.net/ - New and Improved (yes, the popup is
annoying)
http://www.openmymind.net/faq.aspx - unofficial newsgroup FAQ (more to
come!)

 

[tshad]

You would create an instance class with instance members if you wanted to
create an Email object, set it's properties and have a Send() method, ala:

dim email as new Email("some subject")
email.Body = "xxx"
email.Send()


you would use a shared member if you wanted to pass everything in as
parameters

EmailHelp.Send("some subject", "xxx")

I personally prefer the syntax of the 2nd example...but if you wanted to
keep a bunch of different emails, say you wanted to cache them or move
them around between your layers, it'd be necessary to have distinct
instances.

I prefer the 2nd example also.

But when you talk about caching or moving them, are you saying that you want
an instance so you could do something like:

sub somefunction (myEmail as Email)
....
myEmail.somemethod()

end sub

Then using your 1st example:

dim email as new Email("some subject")
email.Body = "xxx"
email.Send()
....
somefunction(email) ' calling the above function


BTW, I took my email function and tried to compile it using:

C:\Inetpub\wwwroot\staffingworkshop>vbc /t:library email.vb
/r:system.web.dll /r:system.data.dll /r:system.dll
/r:Microsoft.VisualBasic.dll

and I get the following errors:

C:\Inetpub\wwwroot\staffingworkshop\email.vb(49) : error BC30469: Reference
to a non-shared member requires an object reference.

I am getting this for request.path and for MapPath.

My file looks like:
**********************************************************************************
Imports System
Imports System.Web
Imports System.IO
Imports System.Web.UI
Imports System.Web.SessionState
Imports System.Web.Mail
Imports System.Data
Imports System.Data.SqlClient
Imports System.Web.HttpCookie
Imports System.Web.HttpCookieCollection
Imports System.Web.HttpResponse
Imports System.Web.HttpRequest
Imports System.Web.HttpApplication
Imports System.Web.HttpApplicationState
Imports Microsoft.VisualBasic

NameSpace MyFunctions

Public Class Email

Public Shared sub sendEmail ( )
dim webMasterEmail As String
dim emailSubject As String
Dim mailServer As String
Dim contactEmail As String
Dim screenTestSubject As String

Dim emailReader As SqlDataReader

Dim ConnectionString as String
=System.Configuration.ConfigurationSettings.AppSettings("MM_CONNECTION_STRING_ftsolutions")
Dim objConn as New SqlConnection (ConnectionString)
Dim CommandText as String = "Select
MailServer,WebMasterEmail,ContactEmail,ScreenTestSubject from emailResponse
where ClientID = '1234'"
Dim objCmd as New SqlCommand(CommandText,objConn)

objConn.Open()

emailReader = objCmd.ExecuteReader

if emailReader.Read then
mailServer = emailReader("MailServer")
webMasterEmail = emailReader("WebMasterEmail")
contactEmail = emailReader("ContactEmail")
screenTestSubject = emailReader("ScreenTestSubject")
end If

objConn.close()

dim URLPath As String = _
Left(request.path, InStrRev(request.path, "/") - 1)

Dim objStreamReader as StreamReader
Dim strInput As String
Dim strBuffer As String

If File.exists(MapPath("..\..\automail\new_account_automail.htm")) then
objStreamReader =
File.OpenText(MapPath("..\..\automail\new_account_automail.htm"))
strInput = objStreamReader.ReadLine()
while strInput <> nothing
strBuffer = strBuffer & strInput
strInput = objStreamReader.ReadLine()
end while
objStreamReader.Close
end if

Dim Message As New MailMessage()
message.To = contactEmail
message.From = webMasterEmail
message.Subject = screenTestSubject
message.Body = "This is line 1<br><br>"
message.Body = message.Body & "This is line 2<br><br>"
strInput = strBuffer.replace("#MESSAGE#",message.Body)
strInput = strInput.replace("#MAILTITLE#","Screen Test Confirmation")
message.Body = strInput
message.BodyFormat = MailFormat.Html
SmtpMail.SmtpServer = mailServer
smtpMail.Send(message)
end sub

End Class

End Namespace
************************************************************************************

This happens whether emailSend is Shared or not.

Thanks,

Tom

 

[tshad]

I prefer the 2nd example also.

But when you talk about caching or moving them, are you saying that you
want an instance so you could do something like:

sub somefunction (myEmail as Email)
...
myEmail.somemethod()

end sub

Then using your 1st example:

dim email as new Email("some subject")
email.Body = "xxx"
email.Send()
...
somefunction(email) ' calling the above function


BTW, I took my email function and tried to compile it using:

C:\Inetpub\wwwroot\staffingworkshop>vbc /t:library email.vb
/r:system.web.dll /r:system.data.dll /r:system.dll
/r:Microsoft.VisualBasic.dll

and I get the following errors:

C:\Inetpub\wwwroot\staffingworkshop\email.vb(49) : error BC30469:
Reference to a non-shared member requires an object reference.

I am getting this for request.path and for MapPath.

My file looks like:
**********************************************************************************
Imports System
Imports System.Web
Imports System.IO
Imports System.Web.UI
Imports System.Web.SessionState
Imports System.Web.Mail
Imports System.Data
Imports System.Data.SqlClient
Imports System.Web.HttpCookie
Imports System.Web.HttpCookieCollection
Imports System.Web.HttpResponse
Imports System.Web.HttpRequest
Imports System.Web.HttpApplication
Imports System.Web.HttpApplicationState
Imports Microsoft.VisualBasic

NameSpace MyFunctions

Public Class Email

Public Shared sub sendEmail ( )
dim webMasterEmail As String
dim emailSubject As String
Dim mailServer As String
Dim contactEmail As String
Dim screenTestSubject As String

Dim emailReader As SqlDataReader

Dim ConnectionString as String
=System.Configuration.ConfigurationSettings.AppSettings("MM_CONNECTION_STRING_ftsolutions")
Dim objConn as New SqlConnection (ConnectionString)
Dim CommandText as String = "Select
MailServer,WebMasterEmail,ContactEmail,ScreenTestSubject from
emailResponse where ClientID = '1234'"
Dim objCmd as New SqlCommand(CommandText,objConn)

objConn.Open()

emailReader = objCmd.ExecuteReader

if emailReader.Read then
mailServer = emailReader("MailServer")
webMasterEmail = emailReader("WebMasterEmail")
contactEmail = emailReader("ContactEmail")
screenTestSubject = emailReader("ScreenTestSubject")
end If

objConn.close()

dim URLPath As String = _
Left(request.path, InStrRev(request.path, "/") - 1)

Dim objStreamReader as StreamReader
Dim strInput As String
Dim strBuffer As String

If File.exists(MapPath("..\..\automail\new_account_automail.htm")) then
objStreamReader =
File.OpenText(MapPath("..\..\automail\new_account_automail.htm"))
strInput = objStreamReader.ReadLine()
while strInput <> nothing
strBuffer = strBuffer & strInput
strInput = objStreamReader.ReadLine()
end while
objStreamReader.Close
end if

Dim Message As New MailMessage()
message.To = contactEmail
message.From = webMasterEmail
message.Subject = screenTestSubject
message.Body = "This is line 1<br><br>"
message.Body = message.Body & "This is line 2<br><br>"
strInput = strBuffer.replace("#MESSAGE#",message.Body)
strInput = strInput.replace("#MAILTITLE#","Screen Test Confirmation")
message.Body = strInput
message.BodyFormat = MailFormat.Html
SmtpMail.SmtpServer = mailServer
smtpMail.Send(message)
end sub

End Class

End Namespace
************************************************************************************

This happens whether emailSend is Shared or not.

I finally got it to work, but not as it should.

To get the MapPath to work I stripped out all but the essential code to
figure it out and plus something I saw on one of the newsgroups.

****************************************************************************************
imports System
imports System.IO
imports System.Web.HttpContext

NameSpace MyFunctions

Public Class Email

Public Shared sub sendEmail ( )
If
File.exists(Current.Server.MapPath("..\..\automail\new_account_automail.htm"))
then
end if
end sub

End Class

End Namespace
********************************************************************

I needed the following:

imports System.Web.HttpContext

And the MapPath changed to:

If
File.exists(Current.Server.MapPath("..\..\automail\new_account_automail.htm"))
then

Not sure how to get rid of Current and Server (I don't need this in my
normal aspx page).

I still haven't figured out the "request" error yet. But this is all hit or
miss.

The MSDN is no help at all. I found this by accident. Isn't there a place
to find this? I should have to play games to get this to work.

MSDN says MapPath is part of the Server object, but nowhere (that I can
find) does it show how to define it in your code.

Tom

 

[tshad]

I finally got it to work, but not as it should.

To get the MapPath to work I stripped out all but the essential code to
figure it out and plus something I saw on one of the newsgroups.

****************************************************************************************
imports System
imports System.IO
imports System.Web.HttpContext

NameSpace MyFunctions

Public Class Email

Public Shared sub sendEmail ( )
If
File.exists(Current.Server.MapPath("..\..\automail\new_account_automail.htm"))
then
end if
end sub

End Class

End Namespace
********************************************************************

I needed the following:

imports System.Web.HttpContext

And the MapPath changed to:

If
File.exists(Current.Server.MapPath("..\..\automail\new_account_automail.htm"))
then

Not sure how to get rid of Current and Server (I don't need this in my
normal aspx page).

I still haven't figured out the "request" error yet. But this is all hit
or miss.

It turns out the same import is used and you have to do code as:

Current.Server.Request.Path

Again, makes no sense and was found by trial and error. If you do just the
request.Path (where request is one of the members) you get the error.

Tom

 

[Karl Seguin]

You've lost me a bit with the mass amounts of code.

That's exactly what I'm saying about moving it around (as a parameter).

As for your error. Objects which you typically program with in your page
and user controls such as Request, Response, Server, ... are there because
they are exposed as part of the System.Web.UI.Control class your page/user
control inherits from (couple levels deep).

Your email class inherits directly from Object, so Request, Response, Server
are meaningless. To get references to these objects within your class
functions, you need to use System.Web.HttpContext.Current which returns the
current context (ie the web request) which exposes the Response, Request,
Server, ...

so you would do:

dim context as HttpContext = HttpContext.Current
if context is nothing then 'possible if someone is trying to use this
class outside of a web-scope
throw new InvalidOperationException("MyFunc needs to be called from web
request") 'maybe you can do something other than throw an exception?
end if
'now you have access to your request and response objects, here's an example
dim request as HttpRequest = context.Request
dim someValue as string =Request.QueryString("blah")


hope that helps..

Karl

--
MY ASP.Net tutorials
http://www.openmymind.net/ - New and Improved (yes, the popup is
annoying)
http://www.openmymind.net/faq.aspx - unofficial newsgroup FAQ (more to
come!)

 

[tshad]

It turns out the same import is used and you have to do code as:

Current.Server.Request.Path

Actually, it's "Current.Request.Path" - no server.

Tom

 

[tshad]

You've lost me a bit with the mass amounts of code.

That's exactly what I'm saying about moving it around (as a parameter).

As for your error. Objects which you typically program with in your page
and user controls such as Request, Response, Server, ... are there because
they are exposed as part of the System.Web.UI.Control class your page/user
control inherits from (couple levels deep).

Your email class inherits directly from Object, so Request, Response,
Server are meaningless. To get references to these objects within your
class functions, you need to use System.Web.HttpContext.Current which
returns the current context (ie the web request) which exposes the
Response, Request, Server, ...

so you would do:

dim context as HttpContext = HttpContext.Current
if context is nothing then 'possible if someone is trying to use this
class outside of a web-scope
throw new InvalidOperationException("MyFunc needs to be called from web
request") 'maybe you can do something other than throw an exception?
end if
'now you have access to your request and response objects, here's an
example
dim request as HttpRequest = context.Request
dim someValue as string =Request.QueryString("blah")

I may be a little dense here.

If I do this:

******************************************************************************
Imports System.Web.HTTPContext
Imports Microsoft.VisualBasic

NameSpace MyFunctions

Public Class Email

Public Shared sub sendEmail ( )
dim URLPath As String = Left(Current.request.path,
InStrRev(Current.request.path, "/") - 1)
end sub

End Class

End Namespace
******************************************************************************

Where I use "Current.request.path" - it works fine.


If I do this:
******************************************************************************
Imports System.Web.HTTPContext
Imports System.Web.HTTPContext.Current
Imports Microsoft.VisualBasic

NameSpace MyFunctions

Public Class Email

Public Shared sub sendEmail ( )
dim URLPath As String = Left(request.path, InStrRev(request.path, "/") -
1)
end sub

End Class

End Namespace
******************************************************************************
Where I have "Imports System.Web.HTTPContext.Current", I get 2 errors:

C:\Inetpub\wwwroot\staffingworkshop\emailold3.vb(2) : error BC30466:
Namespace or type 'Current' for the Imports 'System.Web.HTTPContext.Current'
cannot be found.

Imports System.Web.HTTPContext.Current

and

C:\Inetpub\wwwroot\staffingworkshop\emailold3.vb(10) : error BC30469:
Reference to a non-shared member requires an object reference.

dim URLPath As String = Left(request.path,
InStrRev(request.path, "/") - 1)

You, and the error, say I need to have an object reference. But when I
create an aspx page (where I am using code inside), I don't need this. I
can reference request (and MapPath) directly.

I understood that the difference between code-inside and code-behind was
that you had to explicitly do the imports in a code-behind file). But in
this case, it is even more than that.

That is where I am confused.

Thanks,

Tom

 

[Karl Seguin]

Ok...
Your codebehind file is a class which inherits Page.

Page exposes the request/response/server which is why it just works as is..


Your email class isn't "web aware" since it doesn't inherit from Page or any
other "web aware" classes.

To have webawarness you use System.Web.HttpContext.Current. You cannot
import this because it's a property...you simply can't import properties in
vb.net.

youshould be doing:

Imports System.Web

and in your code use
HttpContext.Current.Request

or, as I showed earlier, use
dim context as HttpContext = HttpContext.Current
dim request as HttpRequest = context.Request


We've covered a lot of ground in this thread

Karl

--
MY ASP.Net tutorials
http://www.openmymind.net/ - New and Improved (yes, the popup is
annoying)
http://www.openmymind.net/faq.aspx - unofficial newsgroup FAQ (more to
come!)

 

[tshad]

Ok...
Your codebehind file is a class which inherits Page.

Page exposes the request/response/server which is why it just works as
is..


Your email class isn't "web aware" since it doesn't inherit from Page or
any other "web aware" classes.

To have webawarness you use System.Web.HttpContext.Current. You cannot
import this because it's a property...you simply can't import properties
in vb.net.

youshould be doing:

Imports System.Web

and in your code use
HttpContext.Current.Request

or, as I showed earlier, use
dim context as HttpContext = HttpContext.Current
dim request as HttpRequest = context.Request


We've covered a lot of ground in this thread

Yes, we have - and I really appreciate it. These are the things that are
hard to get a handle on as it isn't covered well in most of the books I have
(or at least not in the places I have been reading).

If you knew where to find this, it would probably be there - but you have to
find it.

Thanks,

Tom