🚀 go-pugleaf

Hey guys

I am trying to create a 'once-only' app (only one instance can run).
When the user tries to run a second instance, it should pass its command
line to the first instance. I have been following the code at
http://bcbjournal.org/articles/vol3/9911/Single-instance_applications.htm
(and also
http://www.bcbjournal.org/articles/vol3/9911/Using_file_associations.htm)
but I can't get it to work. I'm using C++Builder 6.

Here is the workings of my code (slightly different from Kent's):


//---------------------------------------------------------------------------
// TFORMMAIN.CPP
//---------------------------------------------------------------------------
__fastcall TFormMain::TFormMain(TComponent* Owner)
     : TForm(Owner)
{
     WindowProc = MyWndProc;
}
//---------------------------------------------------------------------------
void __fastcall TFormMain::MyWndProc(Messages::TMessage &Message)

{
     if (Message.Msg == WM_COPYDATA) {
         Caption = "WM_COPYDATA";
     }
     else {
         WndProc(Message);
     }
}
//---------------------------------------------------------------------------


//---------------------------------------------------------------------------
// MUTEXTEST.CPP
//---------------------------------------------------------------------------
WINAPI WinMain(HINSTANCE, HINSTANCE, LPSTR cmdLine, int)
{
     try
     {
         CreateMutex(NULL, NULL, "the mutex of doom");

         if (GetLastError())
         {
             Application->Title = "Something Else";
             HWND hWnd = FindWindow("TApplication", "MutexTest");

             if (IsIconic(hWnd)) {
                 ShowWindow(hWnd, SW_SHOWDEFAULT);
             }
             SetForegroundWindow(hWnd);

             if (strlen(cmdLine) != 0)
             {
                 COPYDATASTRUCT cds;
                 cds.cbData = strlen(cmdLine) + 1;
                 cds.lpData = cmdLine;
                 SendMessage(hWnd, WM_COPYDATA, 0, (LPARAM)&cds);
             }
         }
         else
         {
             Application->Initialize();
             Application->Title = "MutexTest";
             Application->CreateForm(__classid(TFormMain), &FormMain);
             Application->Run();
         }
     }
     catch (Exception &exception)
     {
         Application->ShowException(&exception);
     }
     catch (...)
     {
         try
         {
             throw Exception("");
         }
         catch (Exception &exception)
         {
             Application->ShowException(&exception);
         }
     }
     return 0;
}
//---------------------------------------------------------------------------


Now, the once-only aspect of the app works great. But my WM_COPYDATA
message isn't being picked up at all. If anyone can help at all it would
be fantastic. Thanks!