my code calls a WebMethod. Within that WebMethod I have the need to create a new control collection. In VB I would normally write:
Dim cc As System.Web.UI.ControlCollection = CreateControlCollection()
But because I'm inside a WebMethod, I get the error :
Cannot refer to an instance member of a class from within a shared method or shared member initializer without an explicit instance of the class.
Any suggestions please ?
Thanks folks !
The error message implies you are trying to access an instance-level member or method from a shared method. If you want to access an instance-level method or member from a shared method, first you must create an instance using the new operator and you can access its public members and methods from there on.
Related
I have the following methods:
Public Function RenderRateTable() As String
Private Function RenderRateTable(ToddVersionedObject As ToddVersionedObject,
FieldInfo As FieldInfo) As String
Private Function RenderRateTable(ArrayIndexes As List(Of ArrayIndexesAttribute.ArrayIndex),
ThreeDimensionalArray As ThreeDimensionalDecimalArrayType) As String
Private Function RenderRateTable(ArrayIndexes As List(Of ArrayIndexesAttribute.ArrayIndex),
TwoDimensionalArray As ArrayOfDecimalArraysType) As String
Note that the types that I'm overloading (ArrayOfDecimalArraysType, ThreeDimensionalDecimalArrayType) are not classes that inherit from the same base class. They are different structures that don't inherit from anything. They were written by someone else and I can't change them.
When I call it from within the same class like this
Dim MyThreeDimensionalDecimalArrayType As ThreeDimensionalDecimalArrayType
RenderRateTable(MyArrayIndexes, CType(MyThreeDimensionalDecimalArrayType, Object))
it doesn't go to the right method. It just goes to RenderRateTable().
What's even stranger is, the call is made with two arguments (parameters), but these are (ignored?) and it calls a method that takes no parameters and no run-time error is thrown!
I have Option Strict Off and the variable I'm passing to the parameter ThreeDimensionalArray is of type Object.
I'm trying to get it to where I have a bunch of overloads and it picks the right method based on the type of the Object passed.
Polymorphic method calling instead of an Select Case statement. I hate conditional blocks like that.
UPDATE
I got the code working by declaring the overloads Public, but I still don't understand:
Why the dispatcher wouldn't find the right Private method when the
call is within the same class.
Why the dispatcher would call a method with no parameters when the call is made with 2 parameters, and not throw an error.
You have RenderRateTable() as Public and the rest as Private, which will prevent it from being able to use the correct overload when called from outside the class.
It is very likely that Option Strict On would have pointed out that as a problem: I recommend that you use it to make your programming endeavours easier :)
I'm having a problem because I changed my code from vb6 to .net and I cant seem to sort out this issue I am having. Please assist.
The error message I'm getting:
Error 5 Reference to a non-shared member requires an object reference.
This is happening quite a few places in the code. This is my code. The problem is where it says FrmInvItem.Inv.`
Option Strict Off
Option Explicit On
Public Class ClsInv
Public Function RunProcess(ByVal ConnectStr As String, ByRef Parstr As String) As Integer
Dim frmInvIt As frmInvItem
RunProcess = frmInvItem.Inv(ConnectStr, Parstr)
frmInvIt.Close()
End Function
I assume Inv is not shared, but you are calling it without an instance of the class in which it is. So you either have to make it shared or create an instance of frmInvItem:
Dim frmInvIt As New frmInvItem() ' create instance
RunProcess = frmInvIt.Inv(ConnectStr, Parstr) ' use it on this instance
frmInvItem is the class, you can call a method via classname only if the method is shared.
Shared procedures are class methods that are not associated with a
specific instance of a class. For example, the Cos method defined
within the Math class is a shared method. You can call a shared
procedure as a method of an object or directly from the class.
You are running a method called Inv on a the frmInvIt without creating an instance.
You should create an instance to run your method against:
http://msdn.microsoft.com/en-us/library/77s47661.aspx
Can anyone explain me in VB i need to use Public Shared Sub so it can be accessed from another form.
But what this "Public" and "Shared" means?
Who is public?
With who is shared?
If it is public shared does this means some other software or "some hacker app" can easier have access to this sub and it's values?
In VB.NET, Shared is equivalent to static in C# - meaning the member belongs to the class, not an instance of it. You might think that this member is 'Shared' among all instances, but this is not technically correct, even though VB.NET will resolve a Shared member though an instance invocation.
public class1
public shared something as string
public somethingelse as string
end class
The following code illustrates how VB.Net allows you to access these:
...
class1.something = "something" 'belongs to the class, no instance needed
dim x as new class1() with {.somethingelse = "something else"}
Console.WriteLine(x.somethingelse) 'prints "something else"
Console.Writeline(class1.something) 'prints "something" <- this is the correct way to access it
Console.Writeline(x.something) 'prints "something" but this is not recommended!
...
Public means any linking assembly can see and use this member.
The Public accessor keyword simply means that the method, property, etc. is visible and callable from outside of the DLL or Assembly that defined it.
The Shared keyword means that the method, etc. is not "instanced". That is, it is part of the Class definition only, and not part of the objects that are created ("instanced") from that Class definition. This has two principal effects:
The Shared method can be called at anytime, without actually having an object/instance of that Class. and,
Shared methods cannot access any of the non-Shared parts of the Class definition (unless an object instance is passed to it). They can only directly access the other Shared parts of the Class definition.
I have a Hashtable implementation (in class modules folder).
But I get a strange (long) error, for which no help is provided..
Error throws when I make the Function that return Hashtable Public.
It says:
"Private object modules cannot be used in public object modules as parameters or return types for public procedures (**this is what i need), as public data members, or as fields of public user defined types."
I need very simple logic. I want to be able to get a Function inside one Worksheet to performs some check, fill a Hashtable and return it so I can iterate in it in another Worksheet. Is this even possible (How I do it in C#)
Thanks in advance
The error means that you have your class Instancing property set to Private, which means that you can't use it anywhere where it might get used elsewhere. Mark it as PublicNotCreatable and your error will go away. I'm not clear on what exactly it is you're doing in your app, so that's the first thing to try.
Here is a VB.NET code snippet
Public Class OOPDemo
Private _strtString as String
Public Function Func(obj as OOPDemo) as boolean
obj._strString = "I can set value to private member using a object"
End Function
End Class
I thought we cannot access the private members using the object, but perhaps CLR allows us to do that. So that means that access modifiers are based on the type and not on the instance of that type. I have also heard that c++ also allows that..
Any guesses what could be the reason for this?
Edit:
I think this line from the msdn link given by RoBorg explains this behaviour
"Code in the type that declares a private element, including code within contained types, can access the element "
Your question is quite confusing but I think I've understood it as:
"Why can I access another instance (of my class)'s private variables?"
And you're right - in all OOP languages I've used you can access private variables from other instances, precisely because access permissions are based on where the code is, rather than to which object instance it 'belongs'.
It might be hard to implement copy constructors or equality operators otherwise.
Here's the section about access levels in MSDN.