Pass a value/indicator between projects in DOTNET (C#)

Stephen Clarke

15y3.8k

Hi,

I have a question about passing a value/indicator between projects in DOTNET (VS2010 & C#). Overall these 2 projects create an application which continuously runs on users computers Windows XP, Vista, & Win 7). There is a main project and a Windows service project – the main project runs as an application when a user is logged into their computer, while the service project runs when the user logs out (when computer is back at the login screen). I need to pass a value/indicator between the main project and the service project, so that when the user logs off then if the value/indicator is set by the main project then the service project will recognise this, perform a task and reset/remove this so that it is only called one time (i.e. until the next time that the user logs into the computer and the value/indicators set again.

So far, I have been creating an files (XML) with a value, and saving this as a file on the (Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments) directory, so as to save this to the users MyDocuments directory. I had hoped to then access this when the user logs off (i.e. the last user to log off). However, I can't get the service part of my application to access this using the same special folder.

Overall, I am trying to find out if there is any way for a service project to access an XML file the MyDocuments (Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments) folder of the last user who was logged in, and then if the services project could modify this file to reset this value (as I just want this aspect called once when the user logs out). Alternatively, is there a different or better way to set a value/indicator from an application when the user is logged in, and then for a service project to access this when the user logs out and modify/reset it so that it isn't called continuously. From what I can see, Windows 7 seems to be tricky for permissions, so as to allow the service to both read a file and then modify it.

Hope this makes sense and any help/advice appreciated.

8 Replies

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Stephen Clarke15y ago
Hi folks, I was trying to reply to you individually, but as a reply to all thanks for all your suggestions and information. Just one comment about my wording is that I appreciate that some of my vocabulary may have had more than one meaning. By project, I meant the project within Visual Studio (ie I have a service project and another project). The 'other/main' project is the one which is called when the application starts first, and which in turn calls the service project. Thanks again, Stephen
Stephen Clarke15y ago
Thanks for your reply and information. I think that I have now got this working using winService.Start(string[] args) to start the Service and passing commands as an array of strings at the same time. Then I override the OnStart in the Service part of the solution. Thanks again, Stephen
Vulpes15y ago
It sounds to me like it's only a simple value that needs to be passed between the processes.

I think the managed documentation for named pipes is good enough to do something simple like that but, if it isn't, then I can provide an example myself.
Sam Hobbs15y ago
Also, Stephen, if you could avoid using the term "project" in this context then that will help. That is a beginner mistake. They are either applications or processes or services or class libraries or many other possibilities but the term project is too imprecise; it does not communicate what type of something that the something is.

So the term "main project" is unclear; is it a console application or some other type of application?

If the service is truly a Windows Service then I don't understand "the service project runs when the user logs out". I am not real experienced with Windows Services but what you are saying seems to not be the way that Windows Services work.
Sam Hobbs15y ago
Although there are managed classes for pipes, the documentation of the classes are difficult to figure out unless you have experience with pipes using the API documentation of them. There are many things in the documentation for the managed pipe classes that are missing. It was that way with MFC but at least then we had source code. So what I am getting at is that it seems that the managed pipes classes are there for those that are already familiar with pipes and the rest of us should use .Net Remoting or WCF.
Vulpes15y ago
It sounds to me as though the two processes will not be running concurrently i.e. the service runs when the user logs out but stops when the user logs in again.

However, if there is some overlap then I agree with Sam that you should be able to use named pipes (see http://msdn.microsoft.com/en-us/library/system.io.pipes.aspx for the .NET implementation) which I think are still able to communicate between different sessions under Vista and Windows 7.
Sam Hobbs15y ago
What you are looking for is either Interprocess Communication (IPC) or synchronization. The Windows API documents most of the possible options for doing that, but .Net seems to make the world unclear. Typical IPC mechanisms are named pipes, the copydata message and shared memory. If it truly is a service then named pipes have been the traditional choice for communication and as I understand .Net Remoting and WCF, they can use Named Pipes as a mechanism for communication.

It depends on how much data needs to be exchanged. If no data needs to be exchanged other than the execution of the application, then you probably just need a synchronization facility such as a named event or a named mutex. I forget what they are called in managed code. If you think they will help then look for articles about them and if you have specific questions let us know.
Mahesh Chand15y ago
Just to point you in the right direction, you probably need to looking into delegates and event notifications. You can use .NET Remoting (now WCF) to notify one application from another that includes passing values.