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OOP object instance assignment in sub new()each page of a vb.net website. I can successfully access everything if I include the following at the start of each pageload: Dim objCurrentUser As WebsiteClass.CurrentUser = Session("CurrentUser") If objCurrentUser Is Nothing Then objCurrentUser = New WebsiteClass.CurrentUser Any page can be linked to directly and not force a login, so without the second line I get an object instance error. Right now I only save the CurrentUser object to session on a successful login: If objCurrentUser.IsLoggedIn Then Session.Add("CurrentUser", objCurrentUser) Is there a way to include this logic in the class's new method itself, such as: Namespace WebsiteClass Public Class CurrentUser ... Public Sub New() If Not HttpContext.Current.Session("CurrentUser") Is Nothing Then Me = HttpContext.Current.Session("CurrentUser") End If End Sub End Class End Namespace so that each codebehind would simply need: Dim objCurrentUser As New WebsiteClass.CurrentUser The trouble I have is I can't seem to assign one instance of a class to another from within a method of the class, aka "'Me' cannot be the target of an assignment." Can this be done, or is this unavoidable based on the structure of OOP, or is there another way to move the boolean session operation that will need to occur on each page to the class itself? Thanks in Advance! Brian Syssex,
Maybe I understand you wrong but why don't you pass the New statement to the setting. Be aware that ASPNET is stateless, this means that every object is automaticly disposed after that the page is sent back to the user. I think that you want something as (not tested) If Session.item(user) Is Nothing then redirect to home page for validation purpose else ThisUser = New User(Session.Item(user)) End if Public class User Public Sub New(byval TheUser as String) Do the things you want to do End sub End Class .. I hope this helps, Cor <sys***@gmail.com> schreef in bericht Show quoteHide quote news:1150145001.990347.25860@j55g2000cwa.googlegroups.com... >I have a "CurrentUser" object in session that I want to access from > each page of a vb.net website. I can successfully access everything if > I include the following at the start of each pageload: > > Dim objCurrentUser As WebsiteClass.CurrentUser = > Session("CurrentUser") > If objCurrentUser Is Nothing Then objCurrentUser = New > WebsiteClass.CurrentUser > > Any page can be linked to directly and not force a login, so without > the second line I get an object instance error. Right now I only save > the CurrentUser object to session on a successful login: > > If objCurrentUser.IsLoggedIn Then Session.Add("CurrentUser", > objCurrentUser) > > Is there a way to include this logic in the class's new method itself, > such as: > > Namespace WebsiteClass > Public Class CurrentUser > ... > Public Sub New() > If Not HttpContext.Current.Session("CurrentUser") Is Nothing Then > Me = HttpContext.Current.Session("CurrentUser") > End If > End Sub > End Class > End Namespace > > so that each codebehind would simply need: > > Dim objCurrentUser As New WebsiteClass.CurrentUser > > The trouble I have is I can't seem to assign one instance of a class to > another from within a method of the class, aka "'Me' cannot be the > target of an assignment." Can this be done, or is this unavoidable > based on the structure of OOP, or is there another way to move the > boolean session operation that will need to occur on each page to the > class itself? Thanks in Advance! > > Brian > You can't assign anything to the Me keyword. A constructor (Sub New)
can't return a null reference, it always returns an instance of the class. Use a factory method to get or create the instance: Public Shared Sub GetCurrent() As CurrentUser Dim objCurrentUser As WebsiteClass.CurrentUser objCurrentUser = Session("CurrentUser") If objCurrentUser is Nothing Then objCurrentUser = New WebsiteClass.CurrentUser End If Return objCurrentUser End Sub If you want to use the constructor, you can't return the actual object in the session variable, you would have to copy the information from that object into the newly created instance. That would of course mean that you would have two separate but identical instances, one referenced by the session variable and one created in the page. sys***@gmail.com wrote: Show quoteHide quote > I have a "CurrentUser" object in session that I want to access from > each page of a vb.net website. I can successfully access everything if > I include the following at the start of each pageload: > > Dim objCurrentUser As WebsiteClass.CurrentUser = > Session("CurrentUser") > If objCurrentUser Is Nothing Then objCurrentUser = New > WebsiteClass.CurrentUser > > Any page can be linked to directly and not force a login, so without > the second line I get an object instance error. Right now I only save > the CurrentUser object to session on a successful login: > > If objCurrentUser.IsLoggedIn Then Session.Add("CurrentUser", > objCurrentUser) > > Is there a way to include this logic in the class's new method itself, > such as: > > Namespace WebsiteClass > Public Class CurrentUser > ... > Public Sub New() > If Not HttpContext.Current.Session("CurrentUser") Is Nothing Then > Me = HttpContext.Current.Session("CurrentUser") > End If > End Sub > End Class > End Namespace > > so that each codebehind would simply need: > > Dim objCurrentUser As New WebsiteClass.CurrentUser > > The trouble I have is I can't seem to assign one instance of a class to > another from within a method of the class, aka "'Me' cannot be the > target of an assignment." Can this be done, or is this unavoidable > based on the structure of OOP, or is there another way to move the > boolean session operation that will need to occur on each page to the > class itself? Thanks in Advance! > > Brian > Goran,
Using shared classes in an ASPNET application can be very dangerous. A shared class is forever used by all active users together in the application. Therefore your objCurrenUser, will only be for the first user who starts the application "Nothing". (As long as there are users (sessions), it will after that exist) I know that this is confusing for Winform developers the first time they see that. Cor You are right about using shared classes in ASP.NET, but I'm not talking
about shared classes at all. The code that I'm showing is a factory method, just as I mentioned in the post. If you aren't familiar with the concept, a factory method is used to get an instance of a class instead of directly using the constructor. A factory method is usually a shared method, so that you don't have to create a dummy instance of the class just to be able to call the method. Cor Ligthert [MVP] wrote: Show quoteHide quote > Goran, > > Using shared classes in an ASPNET application can be very dangerous. > A shared class is forever used by all active users together in the > application. > > Therefore your objCurrenUser, will only be for the first user who starts the > application "Nothing". (As long as there are users (sessions), it will after > that exist) > > I know that this is confusing for Winform developers the first time they see > that. > > Cor > > Goran,
You have a datapart in your sample as an object holding information. (You even test if it exist and that is the base of my previous message) Without that it would not be a problem. Moreover, without that data part I use it too. (And for real sharing data between users in an aspnet application instead of a cache) Cor Show quoteHide quote "Göran Andersson" <gu***@guffa.com> schreef in bericht news:%23dhBajxjGHA.456@TK2MSFTNGP05.phx.gbl... > You are right about using shared classes in ASP.NET, but I'm not talking > about shared classes at all. The code that I'm showing is a factory > method, just as I mentioned in the post. > > If you aren't familiar with the concept, a factory method is used to get > an instance of a class instead of directly using the constructor. A > factory method is usually a shared method, so that you don't have to > create a dummy instance of the class just to be able to call the method. > > > Cor Ligthert [MVP] wrote: >> Goran, >> >> Using shared classes in an ASPNET application can be very dangerous. >> A shared class is forever used by all active users together in the >> application. >> >> Therefore your objCurrenUser, will only be for the first user who starts >> the application "Nothing". (As long as there are users (sessions), it >> will after that exist) >> >> I know that this is confusing for Winform developers the first time they >> see that. >> >> Cor >> A datapart? What do you mean?
I have search for the term "datapart", and the only remotely related I found was the usage as "a part of some data". Are you referring to the local variable that is used in the method? That is a local variable that is declared for the method. The scope of the variable is only inside the method, and the lifetime of the variable is only the duration of the call to the method. When the method returns, the variable no longer exists. It's not a shared variable that is stored in the class, if that is what you are thinking of. Notice the lack of the "shared" keyword in the declaration of the variable. Cor Ligthert [MVP] wrote: Show quoteHide quote > Goran, > > You have a datapart in your sample as an object holding information. > (You even test if it exist and that is the base of my previous message) > > Without that it would not be a problem. > > Moreover, without that data part I use it too. > > (And for real sharing data between users in an aspnet application instead of > a cache) > > Cor > > "Göran Andersson" <gu***@guffa.com> schreef in bericht > news:%23dhBajxjGHA.456@TK2MSFTNGP05.phx.gbl... >> You are right about using shared classes in ASP.NET, but I'm not talking >> about shared classes at all. The code that I'm showing is a factory >> method, just as I mentioned in the post. >> >> If you aren't familiar with the concept, a factory method is used to get >> an instance of a class instead of directly using the constructor. A >> factory method is usually a shared method, so that you don't have to >> create a dummy instance of the class just to be able to call the method. >> >> >> Cor Ligthert [MVP] wrote: >>> Goran, >>> >>> Using shared classes in an ASPNET application can be very dangerous. >>> A shared class is forever used by all active users together in the >>> application. >>> >>> Therefore your objCurrenUser, will only be for the first user who starts >>> the application "Nothing". (As long as there are users (sessions), it >>> will after that exist) >>> >>> I know that this is confusing for Winform developers the first time they >>> see that. >>> >>> Cor >>> > Goran,
You are right, I had not good looked at your code the data part of your method is a local variable. And accoording to the idea of it, it could work. However I have never seen the by you used statemens as >:Public Shared Sub GetCurrent() As CurrentUser As well do I not understand how a shared Function which belong to all users can use a Session which belong to one user. I had seen your code as a kind of pseudo but it seems to be reality and in my idea it will throw a lot of errors and never function this way. But I keep it by this. Cor Show quoteHide quote "Göran Andersson" <gu***@guffa.com> schreef in bericht news:Ogem2Y9jGHA.4304@TK2MSFTNGP03.phx.gbl... >A datapart? What do you mean? > > I have search for the term "datapart", and the only remotely related I > found was the usage as "a part of some data". > > Are you referring to the local variable that is used in the method? > > That is a local variable that is declared for the method. The scope of the > variable is only inside the method, and the lifetime of the variable is > only the duration of the call to the method. When the method returns, the > variable no longer exists. > > It's not a shared variable that is stored in the class, if that is what > you are thinking of. Notice the lack of the "shared" keyword in the > declaration of the variable. > > > Cor Ligthert [MVP] wrote: >> Goran, >> >> You have a datapart in your sample as an object holding information. >> (You even test if it exist and that is the base of my previous message) >> >> Without that it would not be a problem. >> >> Moreover, without that data part I use it too. >> >> (And for real sharing data between users in an aspnet application instead >> of a cache) >> >> Cor >> >> "Göran Andersson" <gu***@guffa.com> schreef in bericht >> news:%23dhBajxjGHA.456@TK2MSFTNGP05.phx.gbl... >>> You are right about using shared classes in ASP.NET, but I'm not talking >>> about shared classes at all. The code that I'm showing is a factory >>> method, just as I mentioned in the post. >>> >>> If you aren't familiar with the concept, a factory method is used to get >>> an instance of a class instead of directly using the constructor. A >>> factory method is usually a shared method, so that you don't have to >>> create a dummy instance of the class just to be able to call the method. >>> >>> >>> Cor Ligthert [MVP] wrote: >>>> Goran, >>>> >>>> Using shared classes in an ASPNET application can be very dangerous. >>>> A shared class is forever used by all active users together in the >>>> application. >>>> >>>> Therefore your objCurrenUser, will only be for the first user who >>>> starts the application "Nothing". (As long as there are users >>>> (sessions), it will after that exist) >>>> >>>> I know that this is confusing for Winform developers the first time >>>> they see that. >>>> >>>> Cor >>>> >> A huge thank you again to Cor and Göran! I greatly appreciate the
knowledge you shared! Cor, I've used a lot of functions that reference the session variable using httpcontext.current.session. In the past I've had to create a dummy instance of the "function library" class to get to them like Göran described above. But I plan to try the public shared subroutines mentioned, so that may have just changed! :) Brian Cor Ligthert [MVP] wrote:
> Goran, That is not a problem. The call to the method is still specific for the > > You are right, I had not good looked at your code the data part of your > method is a local variable. > And accoording to the idea of it, it could work. > > However I have never seen the by you used statemens as > >> :Public Shared Sub GetCurrent() As CurrentUser > > As well do I not understand how a shared Function which belong to all users > can use a Session which belong to one user. user. Actually, the shared keyword for methods doesn't really have anything to do with sharing the method between users. As a method only is loaded once into memory, the code for a method is always shared by all users, regardless if the method is declared as shared or not. The shared keyword for a method only means that the method is called without the use of an instance of the class. The "shared" keyword in VB is somewhat confusing when used this way. Consider that other languages uses the "static" keyword instead, which makes more sense in this context. > I had seen your code as a kind of pseudo but it seems to be reality and in No, there is nothing wrong with the code. I assure you that it works > my idea it will throw a lot of errors and never function this way. just fine. Show quoteHide quote > But I keep it by this. > > Cor > > > "Göran Andersson" <gu***@guffa.com> schreef in bericht > news:Ogem2Y9jGHA.4304@TK2MSFTNGP03.phx.gbl... >> A datapart? What do you mean? >> >> I have search for the term "datapart", and the only remotely related I >> found was the usage as "a part of some data". >> >> Are you referring to the local variable that is used in the method? >> >> That is a local variable that is declared for the method. The scope of the >> variable is only inside the method, and the lifetime of the variable is >> only the duration of the call to the method. When the method returns, the >> variable no longer exists. >> >> It's not a shared variable that is stored in the class, if that is what >> you are thinking of. Notice the lack of the "shared" keyword in the >> declaration of the variable. >> >> >> Cor Ligthert [MVP] wrote: >>> Goran, >>> >>> You have a datapart in your sample as an object holding information. >>> (You even test if it exist and that is the base of my previous message) >>> >>> Without that it would not be a problem. >>> >>> Moreover, without that data part I use it too. >>> >>> (And for real sharing data between users in an aspnet application instead >>> of a cache) >>> >>> Cor >>> >>> "Göran Andersson" <gu***@guffa.com> schreef in bericht >>> news:%23dhBajxjGHA.456@TK2MSFTNGP05.phx.gbl... >>>> You are right about using shared classes in ASP.NET, but I'm not talking >>>> about shared classes at all. The code that I'm showing is a factory >>>> method, just as I mentioned in the post. >>>> >>>> If you aren't familiar with the concept, a factory method is used to get >>>> an instance of a class instead of directly using the constructor. A >>>> factory method is usually a shared method, so that you don't have to >>>> create a dummy instance of the class just to be able to call the method. >>>> >>>> >>>> Cor Ligthert [MVP] wrote: >>>>> Goran, >>>>> >>>>> Using shared classes in an ASPNET application can be very dangerous. >>>>> A shared class is forever used by all active users together in the >>>>> application. >>>>> >>>>> Therefore your objCurrenUser, will only be for the first user who >>>>> starts the application "Nothing". (As long as there are users >>>>> (sessions), it will after that exist) >>>>> >>>>> I know that this is confusing for Winform developers the first time >>>>> they see that. >>>>> >>>>> Cor >>>>> > First, thanks Cor and Göran for the help!
The function looks to be just what I wanted as far as putting the test in one location and not in each script, although it sounds like what I'm looking for is not the ideal. :) Am I correct that it would only duplicate the attributes and utilize one copy of the methods? The CurrentUser object also "has-a" object that accesses CurrentUser properties, similar to the code in http://groups.google.com/group/microsoft.public.dotnet.languages.vb/browse_thread/thread/7c8fa285c54b54ca Namespace WebsiteClass Public Class CurrentUser Public AnotherObject As AnotherClass.AnotherObject ... Public Sub New() AnotherObject = New AnotherClass.AnotherObject(me) End Sub End Class End Namespace Namespace AnotherClass Public Class AnotherObject Private _CurrentUser As WebsiteClass.CurrentUser ... Public Sub New(ByRef CU As WebsiteClass.CurrentUser) _CurrentUser = CU End Sub Public Sub AnotherFunction() somehowuse(_CurrentUser.SomeProperty) End Sub End Class End Namespace Will this passing of the CurrentUser to AnotherClass duplicate the object methods? I thought ByRef wouldn't and ByVal would, but it looks like they really mean IN and IN/OUT, so it sounds like I should use ByVal whenever possible, rather than the other way around. And would combining this with the function Göran mentioned result in 4 instances? I sound nit-picky but the CurrentUser object is growing quickly to incorporate a lot of business logic and I'm still trying to get my arms around all this! Brian sys***@gmail.com wrote:
> First, thanks Cor and Göran for the help! There is always only one copy of the methods. An instance of an object > > The function looks to be just what I wanted as far as putting the test > in one location and not in each script, although it sounds like what > I'm looking for is not the ideal. :) Am I correct that it would only > duplicate the attributes and utilize one copy of the methods? doesn't contain the methods, it only has the ability to use the methods. The compiler keeps track of what objects can use which methods. An object instance only contains it's (non-shared) member variables. Show quoteHide quote > The No, nothing is duplicated. The only thing that is sent to the > CurrentUser object also "has-a" object that accesses CurrentUser > properties, similar to the code in > http://groups.google.com/group/microsoft.public.dotnet.languages.vb/browse_thread/thread/7c8fa285c54b54ca > > Namespace WebsiteClass > Public Class CurrentUser > Public AnotherObject As AnotherClass.AnotherObject > ... > Public Sub New() > AnotherObject = New AnotherClass.AnotherObject(me) > End Sub > End Class > End Namespace > Namespace AnotherClass > Public Class AnotherObject > Private _CurrentUser As WebsiteClass.CurrentUser > ... > Public Sub New(ByRef CU As > WebsiteClass.CurrentUser) > _CurrentUser = CU > End Sub > Public Sub AnotherFunction() > somehowuse(_CurrentUser.SomeProperty) > End Sub > End Class > End Namespace > > Will this passing of the CurrentUser to AnotherClass duplicate the > object methods? constructor of the AnotherClass is a reference to the CurrentUser object. As you have declared the parameter as ByRef it actually only accepts a reference variable. As Me is not a variable, the reference is first copied to a temporary variable, and the reference to the temporary variable is sent to the constructor. The compiler creates code that does the same thing as: Dim temp as CurrentUser = Me AnotherObject = New AnotherClass.AnotherObject(temp) As the reference is sent using ByRef, you have the ability to change the variable used in the method call from within the method. In this case that would mean that you would change the temporary variable that was created for the call, but as that variable isn't used for anything once the method returns, the change wouldn't affect anything. > I thought ByRef wouldn't and ByVal would, but it looks Yes, stick to ByVal. All parameters are passed by value unless you > like they really mean IN and IN/OUT, so it sounds like I should use > ByVal whenever possible, rather than the other way around. specify ByRef, so you can omit the ByVal keyword (unless you want to be extra obvious somewhere). When you are passing an object by value, that doesn't mean that the object is copied. It means that the value of the reference to the object is copied. Objects are never copied unless you specifically ask for it. > And would No.> combining this with the function Göran mentioned result in 4 > instances? Show quoteHide quote > I sound nit-picky but the CurrentUser object is growing > quickly to incorporate a lot of business logic and I'm still trying to > get my arms around all this! > > Brian > 
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