C# - Access A Shared/static Member Through An Instance Variable?
Mar 3, 2011
Here's an example of what I'm talking about...
Public Class Sample1
Public Shared Function MyValue() As Integer
Return 0
End Function
Public Sub Code()
[Code]...
Me.MyValue gives a warning in VB.NET and (the equivalent code gives) an error in C#. Is there a particular reason for this? I find it more intuitive/natural to access the shared function using 'Me.MyValue' - but I avoid it to keep my warnings at 0. Did someone else just decide 'Nah, it makes more sense to do it the other way' or is there some technical reason I don't understand?
EDIT: I was thinking of it wrong, more like a 'sub class' in OOP. Even if something is declared in the base class, you access it through the instance you have. But that relationship is not the same with shared or static.
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Jun 2, 2011
how do I overcome it? I have created a class and compiled into .dll This code
[Code]...
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May 31, 2010
In the following code i get a warning at line 59:Warning 1: Access of shared member, constant member, enum member or nested type through an instance; qualifying expression will not be evaluated.and.. At line 78 I get this Warning:
Warning 2 Property 'SelectedCustomer' doesn't return a value on all code paths. A null reference exception could occur at run time when the result is used.
The program compiles and runs well, but i cant' undesrtand the reason for these warnings. Any Idea ?
1: Public Class Form1
2:
3: 'Form level members
4: Private objCustomers As New ArrayList
[code]....
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Aug 4, 2010
I'm a newbie to threading, trying to learn it as I go. don't make any assumptions and try to explain threading concepts and rules that might seem obvious. I have a Module (Static class) as follows:
Module Main
Private ReadOnly _dbConn As SqlClient.SqlConnection
Public ReadOnly Property DBConn() As SqlClient.SqlConnection
Get
Debug.Print("Accessing DBConn")
[Code]...
All throughout the application, when i access DBConn on the same thread, it works as expected. howeve, later on I created a background worker that tries to access DBConn and nothing happens, the thread just hanges (the Background worker). I dont get the printout and the application doesnt continue. the background worker thread doesnt continue past that point, and so the thread never exits. I dont get any exceptions, and i Cant debug in Visual Studio (visual studio hangs).I guess its a 2 part question: why cant i access DBConn from the other thread, and why does it hang without giving me a threadAccess exception? also, why does visual studio hang (I'm assuming it hanges because the thread is hanging)?
Please Note: I am not asking about practice. I know I shouldnt be sharing the same connection, rather returning a new connection. in this particular application it is safe since (although i execute it on a background thread) as per the flow of the application, the connection can only be accessed one at a time. I just want to know why it hangs accross the thread.
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Jun 23, 2009
i changed a class variable to shared so i can access it in all instances of the class, but it caused an error. what is causing this, and how can i fix it?
Private
Shared img As Bitmap
Me
.img = bgImage
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Nov 6, 2009
After I formatted my laptop and reinstalled Visual Studio 2005, I receive a lot of same error as below message.
"Access of shared member through an instance; qualifying expression will not be evaluated"
If I click the error, it direct me to the line and all 102 error suggest me to add "Windows.Forms." before "DialogResult.OK". Should I add something on "Reference"?
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Aug 13, 2009
In Visual Studio 2008, if I do this:
[Code]....
Does anyone here know how to get the above to work WITHOUT warnings being generated?
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Aug 9, 2011
I would like to understand the Pro & Cons in using the commonly used methods via Singleton class against Shared (Static) members of a class in VB.Net. It could be in terms Time, Space complexity or best practices. I have a BankAccount class with methods doing some business logic.
GetBalance()
GetLast5Credits()
GetMiniStatement()
[code].....
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Apr 28, 2011
Cannot appear to be able to get this function to not have the above error.Private Function GetIncidentActions(ByVal FromAgentID As Integer, ByVal ToAgentID As Integer, ByVal incidentAction As Integer, ByVal ActionDate As Date) As String
[Code]...
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Aug 27, 2010
Is it possible to prohibit an instance of a class from calling a shared/static method?
For example:
I want to allow this:
ClassName.MethodOne()
But I want to disallow this:
Dim A As New ClassName
A.MethodOne()
The reason this is desirable is that in this case it is semantically confusing if an instance can call the method.
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Jan 6, 2011
I have the following code:
Public Class TestClass
Public Sub Main()
If theGlobal IsNot Nothing Then Throw New Exception("What gives!")
End Sub
Private Shared theGlobal As Object = Nothing
[Code] .....
Why is theGlobal object NOT Nothing?
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Aug 23, 2011
Will the list in this shared method keep its state throughout the life of the method? Or will a new list be created every time this method is called?
[Code]...
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Jan 28, 2010
I need a static variable to get a ListItemCollection from a List control (I can do this, but if I don't set it as Shared It's not preserving the values as it should). The thing is that this class is a SharePoint webpart, so I most probably will be using the webpart more than once, and I need this variable to be unique to each webpart, which shared doesn't accomplish.I tried everything you can imagine. I placed a Static variable within a Sub (shared and not shared), I tried it with Properties (also Shared and not shared)...
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Mar 13, 2010
I've been trying implement Constructor method in passing variable between two forms.Just a rough user interface guide - issue Invoice. User would type in all the Customer Name, Document Number. Once he reached Item Details, a Child Form would pop-up for the User to select/search the Invoice's Item; Once selected, the selected item would showed in the primary Form.
What I had tried is, the Constructor method worked perfectly when it is self-contain in a new project, yet to be implement in my application.But when I implemented, there is an error: Reference to a non-shared member requires an object reference.
[Code]...
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Apr 7, 2010
How many instances of a shared variable will be created in a class? just one? correct
[code]...
So, in other words, the DocumentDelivery class will only have one instance of RenderList, correct? can somebody confirm?
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Aug 2, 2011
I've used .NET for a long time but I've never really been sure of this warning :-"Access of a shared member, constant member, enum member or nested type through an instance; qualifying expression will not be evaluated"Whilst this is not causing an issue and I've not really experienced this problem a lot with my own code, converting some code from an old .NET project gives 10's of these errors.
Code:
Protected Function GetContentTypeFromString(ByVal TypeString As String) As MailContentType
Select Case TypeString.ToLower
[code]....
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Nov 29, 2011
I'm wondering if this is possible. In my Test function below I want to
Check if T is of type BaseClass; throw an error if it's not.
Get the value of SomeText property of BaseClass.
Class BaseClass
[code].....
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Jun 9, 2012
I have a custom class called "Time" with the following function, for determining if one Time equals another Time.
Public Shared Shadows Function Equals(ByVal Time1 As Time, ByVal Time2 As Time) As Boolean
Dim x(2) As Integer
x(0) = CInt(Time1.Hour)
x(1) = CInt(Time1.Minute)
[code].....
Access of shared member, constant member, enum member or nested type through an instance; qualifying expression will not be evaluated.I know it shouldn't do any harm, just let the compiler skip evaluation, but is it a way of getting rid of this warning?
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Oct 5, 2011
I created an enumeration in a class library... and compiled it into a dll
Public Enum TestEnum
x = 0
End Enum
I then imported this reference to a windows form project as a referenced dll Public Class Form1 Dim mytestenum As TestPublicEnum.TestEnum Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
[Code]...
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Dec 8, 2010
I have an app the writes to the eventlog correctly in xp. The code does not work in win7.
CODE:
I get an error about inaccessable logs:security. I get that. Run as admin it goes away. I do not want to have to do that every time for every user that runs the app. besides they may not have the rights
So I wanted to make an instance of eventlog and set the Log to write to so it does not search the logs and error out on security.
CODE:
Now i get warnings about "Access of shared member, constant member, enum member or nested type through an instance; qualifying expression will not be evaluated."
How the hell else are you to set the log so that the code will work under win7 with normal user rights AND not get this silly warnings?
I have 71 places that I write to the eventlog. that may or may not be too many but that is for another thread.
CODE:
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Jun 22, 2010
re: Access of shared member constant member enum member or nested type through an instance qualifying expression may not be evaluated I understand that this warning means that you should not reference a shared member via an instance. However, in my test case Test2.t.x("3"), I don't understand why it thinks I'm using an instance, since t is also a shared member. Also, note Test3. See what happens when you change declaration of GetObject() As Object to As Test3. I think I understand the behavior (not eval'd until runtime)
[Code]....
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Sep 5, 2011
I am doing work for a client who has lost the source code for one of their VB.Net WinForms applications. The assembly they have is not obfuscated at all. I am trying to recover as much of the source as I can as C# source and have tried several tools for decompiling assemblies, including Reflector, ILSpy and JustDecompile (all the latest versions), but they all produce code with a huge number of errors in them. Because of the large number of errors in the generated code, I am going to ask about the specific errors (in different questions), get more directed answers and in this way try shed some light on why all the tools are having difficulty decompiling this assembly. This question pertains to the fact that the code generated by all these tools always have a large number of invalid member variables (fields) such as the following:
private short $STATIC$Report_Print$20211C1280B1$nHeight;
private ArrayList $STATIC$Report_Print$20211C1280B1$oColumnLefts;
private StaticLocalInitFlag $STATIC$Report_Print$20211C1280B1$oColumnLefts$Init;
why the generated code has these invalid member variables?
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Dec 28, 2010
The context of this question is that I am trying to debug performance issues (apart from the obvious ones I already know about and can find).I inherited a code base (VB.NET) for an ASP.NET app. This is an app that was developed way back in .NET 1.1 days, and was the first .NET app for a lot of the developers who worked on it.
In this code base is a class called DatabaseUtility that contains several Shared Public methods as well as non-Shared Public Functions and Subs for CRUD operations to the database (SQL Server).
It is common in my "BL" that a method creates an instance of the DatabaseUtility which essentially figures out what the connection string should be and opens a connection, as well as giving the developer a handle to the other methods contained within it.Dim utility as New DatabaseUtility()
Once I have that, I start to create parameters that I am going to pass to one of the methods in DatabaseUtility (like GetDataSet). There is a Shared method in my DatabaseUtility called CreateParameter which does essentially that. It creates a SqlParameter object so I can add it to a Parameters collection.
Now, the code base is littered with a lot of this:
utility.CreateParameter(...)However, because CreateParameter is a Shared method, I am not sure what is going on behind the scenes. I know because it is a Shared member that an instance of the DatabaseUtility is not created when I call it like this:DatabaseUtility.CreateParameter(...)
However, because I am calling it from an instance (utility), does that change the behavior at all?
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Jun 20, 2012
Inside my .aspx I have some JSON code that looks like this:
[Code]....
Basically what I'm doing is pulling text from two labels on one page, and sending them to another page by calling the "doIt" function which looks like this:
[Code]....
Just so I'm clear, the "doIt" function and the JSON call are on two separate web forms. My problem is that with the "doIt" function being Shared, I can't access any global variables of the class. And if I remove the Shared, my JSON doesn't execute.
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May 4, 2009
I've got a shared class (static in C#) which mostly carries some settings data that any class in the application can read and sometimes write. Also there are some static properties which holds some internal states.
Now I want to revert this class to initial stage of it. With all default variables etc. Assume that the user want to reset the current state and start over without restarting the application.
In a singleton model I'd simply renew it with something like this :
Public Sub Reset()
_Instance = New MyClass()
End Sub
However this is not possible in a Shared class. Or should I switch back to Singleton?
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Oct 27, 2009
I Want to know which one is preferred while coding to use Static Methods or normal instances, I prefer to use static if they where few but if there was many of them I start to get some doubts
[code]...
if the EmployeeManager Has Many methods (selects deletes updates) is it ok to make them all static.and if it was Normal instance. wouldn't be a drawback if the object is initiated every time specially if GetAllEmployees() is heavily used.What is the better approach to use?
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Jun 22, 2009
exact diff b/t Static v/s Shared variables in VB.NET?
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Sep 27, 2009
I'm creating a Shared (static) method in ASP.NET MVC so it can be used by any controller in my project. This static method needs to generate a URL. I think I need to use System.Web.Mvc.UrlHelper, but I can't figure out how to call it from within a static method.The constructor seems to want a RequestContext.
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Dec 30, 2009
how I can dynamically load a control inside of a shared/static function?The function itself is inside of a mustinherit/abstract class.(It's an ASP.NET project in VB) I want to do something like this:[code]I'm getting "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.",but I don't understand this error.I understand what it means, I just don't understand why calling LoadControl isn't seen by the compiler as being an explicit instance of the class. What's not explicit about using LoadControl to create a new control from a file? I tried creating a new user control and initializing it, then setting it to a different control with LoadControl to no avail.I also don't want to do a DirectCast because I'm trying to put this in a shared, mustinheret (abstract) class, which therefore doesn't have an .aspx file to write in a <%@ Reference Control="~/SomeControlPath.ascx" %>, so the class name is unavailable.What I'm trying to do is write a static function that takes some value and returns a control based only on that control's source file location.The end result is a user-modifiable list of controls.They get a column of controls that they freely add, remove, or reorder based on a static list of available child controls that I specify.
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May 25, 2010
[using VB.NET, but I can easily read C# code in responses]I have a class called QuestionClipboard with ALL shared methods/properties. I previously had a QuesitonClipboard.doesClipboardHaveContent function that returned true/false if there was a Object on my 'clipboard'.I'd prefer to implement a Dependency Property so I can allow this true/false value to participate in data binding.The "GetValue(dp as DependencyProperty)" method requires an object instance, which would mean that my Property CAN'T be shared!Here is what the code would look like in my perfect world... Of course, the word "Shared" before the property declaration renders this code useless.
Private Shared clipboardHasContentPropertyKey As DependencyPropertyKey = DependencyProperty.RegisterReadOnly("clipboardHasContent", GetType(Boolean), GetType(QuestionClipboard), _
[code]....
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