Static function, send message to hidden window

Hi Experts,

I'm using a named pipe to do IPC.  My callback function is static.  When I receive commands from this pipe, I need to call my instance class somehow - the only way I could think of was with SendMessage.  However, my AfxGetMainWnd is returning NULL since I'm not showing my window.  The reason:  this app is only displaying a system tray icon, so the main window is invisible.  How can I communicate with my class from the static callback?

Thanks,
Mike
LVL 1
threadyAsked:
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pgnatyukCommented:
Add a static variable (pointer to the instance of your class) into the cpp-file with your static function. This static variable you can use in the static function.

Not in this case probably, but, for example, a first parameter of this static function can be the object you need to use in the static function. So in the function you can access all its public methods.

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trinitrotolueneDirector - Software EngineeringCommented:
Lets look at the situation on your hands. Try analyzing whether it is absolutely essential to have a static callback function in the first place.

If you are performing some form of IPC I would suggest that you look at maintaining the abstraction of object communication. In such a case your callback function should also be serving an object.
In other words I am asking you to check whether you can make the callback function non-static.

Still if this cannot be avoided there is another alternative you might want to consider:

make the callbacks free functions in a separately named namespace. See my snippet below:
trinitrotolueneDirector - Software EngineeringCommented:
oops my snippet didnt get attached
namespace MyCallbacks
{
 rettype cb1(arg1, arg2 ..);
 rettype cb2(arg1..);
 ..
 ..

 rettype cb1(arg1, arg2)
 {
   Objecttobecommunicatedwith* ptr = new Objecttobecommunicatedwith()
   ptr->method()
 }

...
..
}

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jkrCommented:
Even if your window is hidden, 'FindWindow()' (http://msdn.microsoft.com/en-us/library/ms633499(VS.85).aspx) will still return a handle. So you could
HWND hWnd = FindWindow(_T("Window Name"),_T("Class Name or NULL"));

SendMessage(hWnd,WM_MYMSG,0,0);

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threadyAuthor Commented:
Thanks pgnatyuk, I don't know why I didn't think of that!

trinitrotoluene, that looks nice and clean, but can you think of a way to do it without creating a new object to call its method?  i.e., can i make my callback point to a specific object?

jkr, that looks dirty!  ;-)   but it would work....
jkrCommented:
>> jkr, that looks dirty!  ;-)

Absolutely not, that's a standard procedure on Windows.
threadyAuthor Commented:
jkr - how do I name my window?  The window happens to be the mainframe so there's only 1, but isn't there a chance that another instance of the program could have the same name?  How do you resolve the ambiguity?

threadyAuthor Commented:
pgnatyuk:  I created my static pointer as you suggested, just to get this working quickly, but I get a compiler error:

MainFrm.obj : error LNK2001: unresolved external symbol "public: static struct HWND__ * CMainFrame::m_hWndInstance" (?m_hWndInstance@CMainFrame@@2PAUHWND__@@A)

Why is it unresolved?
threadyAuthor Commented:
I really hate how c++ differes from java in its handling of statics....  I can never get it through my think head...  I always run into this problem whenever I use statics and I can't remember what to do...  I seem to remember needing to declare some other kind of forward declaration or something....
threadyAuthor Commented:
thick head...  not think head...  :-)
pgnatyukCommented:
You added a static variable to your class. So you need to initialize it in the cpp-file.
HWND CMainFrame::m_hWndInstance = NULL;

You need to assign a value to this variable after you create the window, and set it to NULL when you are destroying it.

jkrCommented:
>>how do I name my window?

Since you are using MFC, the Window name should be placed in the resources.
jkrCommented:
BTW, if you can't locate it there, you can use Spy+ to find out what the title and the class name are.
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