How to launch application from service on current user's desktop?

I have a service that I need to launch a forms application whenever a user logs in. This I have done, no problem, however if this user logs off using "switch user" instead of "log off", and then a new user logs in under a different account, my service will launch the application on the original user's desktop, instead of the new user's desktop. How can I fix this so that the application will launch on the correct desktop

In my OnStart() method for the service, I start a Management Event Watcher, checking for Win32_LogonSession. When the event fires, I launch my application using process.start.

This sucks. In my testing, I guess that programs launched from a service, are launched under the same SessionID as services.exe. So basically who ever logins in first, launches services.exe which in turn initializes all the services installed on the computer.

Upon startup, Services.exe enumerates through all registry subkeys located under the HKEY_LOCAL_MACHINE\Services registry key in the protected registry, where each subkey represents a service. Services.exe then uses the information located in the subkeys to initialize each service, one at a time, and in the order specified in the registry.

Is there any way to change the session ID of a running application

My service is running as local system. In vista, at this present time, I believe vista does support interaction with desktop, its just that all services run under sessionID 0 or something like that, so that the logged in user will never see the application running nor be able to interact with it. I guess technically if you can tell a program to run under a different sessionID, then you could make it work on vista as well.

I have seen video of a service interacting with desktop on vista. When launched, vista prompts the user if they want to view the desktop for the application that was launched. If user agrees, they are taken to that sessionID 0, and then see the application running........ Something like that anyway.....

Hmmm, no I figured that would just launch the process under whatever sessionID started my service, using the credentials provided in the call to CreateProcessAsUser.

As far as the techniques. I was using Process.start, and have since changed that to run my process(yes a gui window) on a thread started from the my services OnStart method. I had to make the window modal, and it seems to work fine, although I dont know how safe this is.

Hmm this looks very promising

SUMMARY

I'm not too sure, but this might be what I need. All I'm trying to do is launch a program or a thread on the current interactive desktop. If I read this correctly, the function will fail, if the thread calling SetThreadDesktop has a window or hook. Sooooo, basically as it stands now, my current threadproc calls a form.showdialog() to display a modal form, which in the form load event, installs a hook. If I make the call to SetThreadDesktop, before I show the form, shouldnt it be successfull, and the subsequent call to show my modal form appear on the desktop that I specified

http://msdn2.microsoft.com/en-us/library/ms686250.aspx

BOOL WINAPI SetThreadDesktop(
 HDESK hDesktop
);

First problem. How do I get the handle to the current interactive desktop I know I use OpenDesktop, but how do I get the "Pointer to null-terminated string specifying the name of the desktop to be opened" As indicated for the LPTSTR lpszDesktop parameter

HDESK WINAPI OpenDesktop(
 LPTSTR lpszDesktop,
 DWORD dwFlags,
 BOOL fInherit,
 ACCESS_MASK dwDesiredAccess
);

Man all this desktop stuff is pretty cool. I like how easy it is to simply create another desktop, and switch to it, or switch to an existing desktop. Anyways, I think maybe this might be my solution. Using OpenInputDesktop. If I understand this right, this will return the handle for the current interactive desktop, or in Microsoft's terms, the desktop that receives user input.

HDESK WINAPI OpenInputDesktop(
 DWORD dwFlags,
 BOOL fInherit,
 ACCESS_MASK dwDesiredAccess
);

I'm trying to have a thread run on the current interactive desktop. I am doing this so that I can launch a thread with a GUI from a service on whatever desktop is currently active. I may switch this over to launch a process instead of a thread, but thats irrelavent at this time

My test code for Form1 containing 1 button named button1

Each time the button is clicked, the first MessageBox shows a number. This number changes everytime the button is clicked. The second MessageBox always returns false, which indicates the thread was not assigned to the desktop.

I'm not confident on my API declares, especially dwDesiredAccess. Perhaps this has something to do with it.

Anyone have some suggestions

Ok it worked. I passed the value 0x0000037f to dwDesiredAccess which gives all access. The handle for the desktop returned is 0. Which is the sessionID that my current desktop is running The 2nd messagebox appeared

Thank you Peter Ritchie.