DWinLib - The Guts

// --------------------------------------------------------------------------------------- //
// This is the entry unit into the BareApp program.  It checks for multiple instances and  //
// sets up the DWinLib application.                                                        //
// --------------------------------------------------------------------------------------- //

#include "PrecompiledHeaders.h"
#pragma hdrstop

#include "DwlApp.h"
#include "CharArrayWrappers.h"


//The method used to determine if there is another instance of this application running is
//http://www.codeproject.com/cpp/avoidmultinstance.asp.  Note that this gives a single
//instance per machine, not a single instance per user.  Newcomer's article shows how to
//extend this for the second requirement.

uint UWM_YOU_ARE_ME;

BOOL CALLBACK searcher(HWND hwnd, LPARAM lParam) {
   DWORD result;
   LRESULT ok = SendMessageTimeout(hwnd, UWM_YOU_ARE_ME, 0, 0, SMTO_BLOCK |
               SMTO_ABORTIFHUNG, 200, &result);
   if (!ok) return TRUE;
   if (result == UWM_YOU_ARE_ME) {
      HWND * target = (HWND *)lParam;
      *target = hwnd;
      return FALSE;
      }
   return TRUE;
   }


int WINAPI WinMain(HINSTANCE inst1, HINSTANCE inst2, LPSTR str, int show) {
   //For your own app, change the text accordingly using GUIDGEN.
   UWM_YOU_ARE_ME = RegisterWindowMessage(_T("MyApp-AE383CB7-EA7D-4f75-BAE5-0B46E2453DF3"));

   //Check to see if it is already running.  ERROR_ACCESS_DENIED is returned when
   //two or more user sessions are running on a computer, and it is running in another
   //session than the one the user is currently logged onto.  Of course, I don't believe
   //Windows allows you to 'Show' an app another user is running in your current session,
   //so you will not be able to run it in a second session.  Hmmmm....
   HANDLE mutex = CreateMutex(NULL, FALSE,
               _T("MyAppA-AE383CB7-EA7D-4f75-BAE5-0B46E2453DF3"));
   bool alreadyRunning = (GetLastError() == ERROR_ALREADY_EXISTS ||
               GetLastError() == ERROR_ACCESS_DENIED);
   if (alreadyRunning) { // kill this one
      Sleep(10);  //Give other window time to open up if necessary
      HWND window = NULL;
      EnumWindows(searcher, (LPARAM)&window);
      if (window != NULL) {
         SetForegroundWindow(window);
         if (IsIconic(window)) ShowWindow(window, SW_RESTORE);
         if (*str != '\0') {
            COPYDATASTRUCT cds;
            cds.dwData = UWM_YOU_ARE_ME;
            cds.cbData = s_cast<int>(strlen(str)+1);
            cds.lpData = str;
            ShowWindow(window, SW_SHOWNORMAL);
            SendMessage(window, WM_COPYDATA, 0, (LPARAM)&cds);
            }
         }
      return FALSE;
      }

   FlexiCharWrap winTitle(_T("Stupid Squares"));
   DwlMdiApp app(inst1, inst2, str, &winTitle, show);
   WPARAM ret = app.run();
   
   CloseHandle(mutex);  //Technically, you don't have to do this. Windows will close it
                        //automatically upon process termination.
   return s_cast<int>(ret);
   }