Implement The Singleton Pattern For Access Via WCF?
Aug 17, 2010
I'd like to expose some functionality via a WCF service. I can configure WCF to instantiate a class per-request but am unsure how I can get a reference to a communal singleton if I were to have some functionality to store a list of calls to a method (call it LogMethod) via WCF in memory and return that list when the GetLogs method is called
I'm aware I could use a database/the file system to pass this data back an forth but in many cases, that seems to be overkill. Edit: It seems that nobody has a clear answer - I can't believe this is complex. Am I missing something obvious?
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Oct 16, 2009
Im trying to Implement the Singleton Pattern and im wondering if this is "Thread Safe" or if I am going to have to explicitly perform a SyncLock on the object instance? Example:
Public NotInheritable Class SingleTon
Private Shared _singleton As SingleTon
Private Sub New()
[Code].....
I tried it both ways, using the SyncLock and without, just not sure which one to be using?
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Jul 23, 2010
I am normally a c# programmer but am now working in VB for this one project when I use to set up a singleton class I would follow the Jon Skeet model
public sealed class Singleton
{
static Singleton instance = null;
static readonly object padlock = new object();
[code]....
I get StackTracker.Instance.Instance and it keeps going, while it is not the end of the world it looks bad.is there a way in VB to hide the second instance so the user can not recursively call Instance?
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Jul 5, 2010
I am working on creating a customized UI composite control. This control would be a container to several other custom controls.As a first step, i am creating the container UI using a singleton pattern. This is because at any point in time only one isntance of this container is allowed to be created. This is fine.Now i want to practice interface based desgin. So i introduced a sinple interface calleD IdesignSurface which has two properties. I would like my singleton class to implement this interface,so i tried something like this and got an error saying "end of line
NotInheritable
Class DesignSurface
implements IDesignSurface
[code]......
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Apr 16, 2011
I have a table, Users, with a related child table, UserSecurityGroups. In my GUI, the operator would select a user from a list. The program would retrieve the user record and allow the operator to edit the user data in one form. The operator could also edit the UserSecurityGroups of this user on another form.
I am considering using a singleton class for user instance retrieval and persistance back to the database. If this is a good practice, I want to use this with many other tables in my DB. My question is: Is this a good practice? What pitfalls am I missing? What would you recommend as an alternative? Would your recommendation change since I also have tables with three or four levels of relations (as opposed to two in the example above)?
Here is my proposed code:
Imports System.Data.Linq
Public Class UserConduit
Implements IDisposable
[code]....
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Nov 18, 2009
Implement singleton in a parent class.Infact what I want is that All the childs etc. should use same instance of the parent.
I have implemented singleton, Changed the scope of parent class's constructor to "Protected". But in the application when ever the new child's constructor is called i.e. "Dim abc as New Ch1()" the constructor of Parent is called (as it is Proctected and can be access from child).
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Mar 18, 2010
So I've been doing some research on the singleton factory design pattern, and I am wondering if my example implementation is correct (warning I did get carried away creating animals):
[Code]...
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Jun 7, 2011
is it possible to implement strategy pattern with different parameters in VB.net? For example I have the following code:
Public Interface InterfaceDataManipulation
Sub updateMyData()
End Interface
How to implemente updateMyData in the class that implements above interface class with different parameter,for example in class x :
Public Class X
Implements InterfaceDataManipulation
Public Sub updateMyData(ByVal x as String)[code]......
But the IDE raises an error "class x must implement updateMyData on interface InterfaceDataManipulation"
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Nov 8, 2009
I have written this code implemeting MVC design pattern.... for simplcity... i have create Model with BLL having a two classes Employee and Designation and i have created the DAL using the Dataset designer tool....thus i've implemted all relationship bewteen the two tables Empoyee and Designation connected to each toher using field EmpIndex.
In MVC design pattern i should return objects to the controller (in this case i used only the view- win form) becuase of my Designer created DAL i cannot return objects of Employee and Designation to the View... this is becuase in BLL: the following method
Code: public TestMVCWithDataset.TestDataSet.tblEmployeesDataTable SearchByIndex(int iEmpIndex) { try { empAdapter.Fill(dtEmployees, iEmpIndex); return dtEmployees; } catch { throw new Exception("Employee not found!"); } }
[code]....
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Nov 6, 2010
Anyone here kind enough to give me a code review on the following pattern that I have used for database access? I have provided one of the simpler datalayers to show the basic idea.In particular I am starting to question if using shared methods was a good idea and what problems may arise from that? Will this implementation fail in a threaded environment like ASP.Net?
Public Interface IFillable
Sub Fill(ByVal Datareader As Data.IDataReader)
End Interface
[code].....
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Jan 19, 2011
Anyone here kind enough to give me a code review on the following pattern that I have used for database access? I have provided one of the simpler datalayers to show the basic idea.In particular I am starting to question if using shared methods was a good idea and what problems may arise from that? Will this implementation fail in a threaded environment like ASP.Net?
[Code]...
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Oct 15, 2011
I am trying to implement datagridview using b.net and ms access.While I import the data from database, the connection is established and test connection succeeds. But, during the last phase, i get an error saying :
Could not load type 'Microsoft.VisualStudio.DataDesign.SyncDesigner.syncFacade.SyncManager' from assembly 'Microsoft.VisualStudio.DataDesign.SyncDesigner.DslPackage, version 9.0.0, Culture=neutral,PblicKey Token=b03f5f7f11d50a3a'
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Sep 24, 2009
I am in the beginning stages of writing a VB.NET application for our customer's pc.This app will monitor machines through a serial port and display the status of those machines on the screen. In the future, we want to be able to run this program both on the pc and from any computer connected to the internet. What steps should I be taking now to make the web access step easier to implement?What is a good resource for learning how to make an application web accessible?
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Jan 15, 2010
I typically dont create interfaces unless i have to, however in my current application i have to create interfaces in the Data access layer. I'm a in a minor confusion that hwo do i create those interfaces more how to implement them: the following code might make things clear:I have the following class and interface in the data access namespace
[code="vb"]Imports ConsoleApplication8.BusinessLayerImports ConsoleApplication8.DataAccessLayerImports System.DataImports System
Namespace DataAccessLayer
Public Class CountryGateway Implements ICountryGateway
[code]....
1. Is this way implement the interface in the data access layer? (in this case the class CountryGateway access the database.)
2. I have been told that we should create interfaces than abstract classes espcially in the data access layer, is there a particular reason for this?
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Dec 17, 2009
I've now properly started implementing OO into my system (which I probably should have done from the start) but I just want to clear some best practices.So let's say I have a class called Job which contains information such as Description, Project Manager (Employee class), Value etc. at the moment, if I initialise the Job class it will initialise all the information held within it, even if I only want the job description. Is it best practice to do this or is it better to implement the class and access the database for values as and when they're needed? Or is it just better in those cases to just access the database directly?
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Jul 29, 2010
how variables declared with protected access in a base class are used to implement inheritance.
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Sep 27, 2011
I have been requested to implement a login form into a friend's Visual Basic .NET application. He specifically requested that I should do this using LINQ to compare the input to a table in an Access database. I don't really know why he imposed these restrictions, but who am I to judge? However, the problem is I am not overly familiar with VB .NET, or LINQ.
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Nov 6, 2009
Sometimes there is a need to initialize the singleton class with some helper values. But we can't "publish" a constructor for it. What is the workaround for this?overloading the GetInstance or setting a color is not my idea. The color should be set only once. I would like to be sure that MyPainter paints ONLY with the initialized color. Any default color should ever be used.
For more clarity I provide a sample:
''' <summary>
''' Singleton class MyPainter
''' </summary>
Public Class MyPainter
[code]....
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Jan 19, 2010
I have recently discovered the singleton approach to mdi child forms and I was trying to integrate this singleton stuff into my "mChildform" class but I keep getting InvalidTypeCastException when I do so. Not sure where I am messing this up.
My mChildform class inherits Form and adds a few properties that are required by all child forms. All of my other project forms inherit this mChildform as their base type instead of form.
When I go directly to one of these forms (the logs form for example) and add
[code...]
I get the exact results that I want. Naturally, since this is something I want all child forms to be able to do I try to add it to my mChildform base class.
The code compiles, but since the reference is of mChildForm type I want to cast it to my usable form class, but it throws the InvalidCastException.
[code..]
I'm not sure why I can't cast it to the other form type, but i'm hoping someone here can explain why I cannot. The Instance() check would always fail if I do not cast my instance to another one of the types.
Since my mChildForm class only holds minimal info to do any real work I have to cast it to the other type. As a workaround I can add the instance method to each new form but I would really like to get it into the base class.
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Jan 26, 2009
In the Designer of my forms I usually have this for Singleton purposes.[code]Is there any hack in the IDE that would let me just press a button or something and it will automatically add the code I have above to the selected Designer?I can always type or copy/paste/modify it but I thought there could be something that I could set to just automate this redundant task.
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Sep 8, 2010
I have an web application written in ASP.NET (FW 3.5) (along with some VBScript, this is a legacy app) that uses a utility class in the backend that logs error. I need to log several values that a user has entered in the front-end. Since the utility class has no access to the front end (or any HTTP services), i created a singleton class within the utility namespace that my front end UI can access and store information about the user.
I guess more specifically, I am wondering if there's a way to store session variables that can be shared across the web application and web services through a class referenced by both of the application and web services. For example, I have an error handling class that is used by both instances that required information about the user. Is there a way to create a per-session singleton to hold that information, so that my error class will have access to the user info?
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Jun 11, 2009
Reading about singletons classes/pattern gave me a pretty good idea for its use. But would it be a good practice to store user related variables in properties of a thread safe singleton class so i can access them by chaining?
Example
When a user logs in several variables will be assigned to a session variable like:
Session("UserID") = reader("UserID")
Session("AccessLevels") = reader("Accesslevels")
Session("UserName") = reader("UserName")
...
Now when working on my webapplication i could always access these values by calling the session() variable, but the chance to forget the session keys or erroneous write them down is significantly. So again would it be good to store these session variables in readonly properties of singleton class so I can access them like:
MySingleton.ID
MySingleton.Accesslevels
MySingleton.UserName
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Jun 27, 2012
So I took this from an example. GetInstance() is called from hundred different places in my program, and when I debug, the line "Prog = New Program" keeps getting hit for each of those calls. Which I thought was exactly what should NOT happen.. Or do I have some fundamental misunderstanding?
[Code]....
It seems the "New" sub triggers a number of calls to Program.GetInstance, before the first one completes. This is due to me earlier having lots of shared public objects in this class, which are no longer shared since the class was made singleton. And these objects, when initialized, calls the Program class for reference to other of it's objects.
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Mar 8, 2011
I have an Addin for MS Excel which needs a singleton to share data amongst modules.Depending on the version of Excel (2003, 2007, 2010), and how Excel was started, it calls my addin from different, unpredictable AppDomains, which prevents the classic singleton approach.Creating a custom AppDomainManager won't work because Excel has already created the AppDomains before the addin is called.
Linking to mscoree to enumerate domains breaks the addin registration process (and I really don't want that anyway); there doesn't seem to be any other way of enumerating, so that isn't an option either.The only solution that I've found is to use remoting. Here's my test rig:
Imports System.Runtime.Remoting
Imports System.Runtime.Remoting.Channels
' Remeber to add reference to System.Runtime.Remoting DLL[code].....
Once everything is running, access to the singleton takes ~100µS, which is perfect. I can live with the ~400mS the first time each AppDomain is initialised. The problem is at startup, where the remoting invocation takes ~2.5 seconds.
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Jun 6, 2011
Explain Singleton architecture of Remoting.
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Nov 18, 2009
implement singleton in a parent class. Infact what I want is that All the childs etc. should use same instance of the parent.
I have implemented singleton, Changed the scope of parent class's constructor to "Protected". But in the application when ever the new child's constructor is called i.e. "Dim abc as New Ch1()" the constructor of Parent is called (as it is Proctected and can be access from child). Which is undesired behaviour.
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May 19, 2011
Testing a configuration of a Windows 7 workstation acting as a "server" and a Windows XP workstation acting as a "client" (also fails in the same way using a Windows 7 client workstation).
[Code]...
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May 10, 2012
I am trying to create an interface and then about 3 or 4 singleton classes that would be accessed via the interface.I know how to get interfaces to work and I know how to create concrete singleton classes and access them via GetInstance(). But when I put the two together, failure results.My problem is in the GetInstance method of the concrete singletons as in
Public Class MovingList
implements ISelectedList
[code]....
ISelectedList is the interface. This fails because ISelectedList.GetInstance is not of the type MovingList. Plus there is a problem with the use of Shared that I think is solved by simply deleting it (interfaces implicitly share).I can't define the type of ISelectedList.GetInstance because each of my singleton classes is of a different type even though they implement exactly the same properties and methods.How best to implement such singleton classes? I could do away with the interface and simply deal directly with the concrete singletons but that feels like bad practice. Programming to an abstraction not an implementation and all that.
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Nov 28, 2011
I have a VB.NET singleton class which implements Serializable:
Imports System.IO
Imports System.Runtime.Serialization
<Serializable()> Public Class CoordinateHistory[code].....
My problem is that I can't actually call .Serialize() on the instance of this class, like all of the examples online show. What am I doing wrong?
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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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