Книга: Microsoft Windows Embedded CE 6.0 Exam Preparation Kit

? Enable Power Management Notification Messages

? Enable Power Management Notification Messages

1. Continue to use the HelloWorld application in Visual Studio.

2. Generate power-management notifications in more frequent intervals by going into the subproject registry settings and setting the registry entry for the UserIdle timeout in AC power mode (ACUserIdle) to five seconds:

[HKEY_LOCAL_MACHINESYSTEMCurrentControlSetControlPowerTimeouts]
 "ACUserIdle"=dword:5 ; in seconds

3. In the ThreadProc function, create a message queue object:

// Size of a POWER_BROADCAST message.
DWORD cbPowerMsgSize =
 sizeof POWER_BROADCAST + (MAX_PATH * sizeof TCHAR);
// Initialize our MSGQUEUEOPTIONS structure.
MSGQUEUEOPTIONS mqo;
mqo.dwSize = sizeof(MSGQUEUEOPTIONS);
mqo.dwFlags = MSGQUEUE_NOPRECOMMIT;
mqo.dwMaxMessages = 4;
mqo.cbMaxMessage = cbPowerMsgSize;
mqo.bReadAccess = TRUE;
//Create a message queue to receive power notifications.
HANDLE hPowerMsgQ = CreateMsgQueue(NULL, &mqo);
if (NULL == hPowerMsgQ) {
 RETAILMSG(1, (L"CreateMsgQueue failed: %xn", GetLastError()));
 return -1;
}

4. Request to receive notifications from Power Manager and check the received messages:

// Request power notifications
HANDLE hPowerNotifications = RequestPowerNotifications(hPowerMsgQ,
 PBT_TRANSITION | PBT_RESUME | PBT_POWERINFOCHANGE);
DWORD dwCounter = 20;
// Wait for a power notification or for the app to exit
while(dwCounter-- &&
 WaitForSinglObject(hPowerMsgQ, INFINITE) == WAIT_OBJECT_0) {
 DWORD cbRead;
 DWORD dwFlags;
 POWER_BROADCAST *ppb =
  (POWER_BROADCAST*) new BYTE[cbPowerMsgSize];
 // loop through in case there is more than 1 msg.
 while(ReadMsgQueue(hPowerMsgQ, ppb, cbPowerMsgSize,
  &cbRead, 0, &dwFlags)) {
  switch(ppb->Message) {
  case PBT_TRANSITION: {
   RETAILMSG(1,(L"Notification: PBT_TRANSITIONn"));
   if(ppb->Length) {
    RETAILMSG(1,(L"SystemPowerState: %sn", ppb->SystemPowerState));
   }
   break;
  }
  case PBT_RESUME: {
   RETAILMSG(1,(L"Notification: PBT_RESUMEn"));
   break;
  }
  case PBT_POWERINFOCHANGE: {
   RETAILMSG(1,(L"Notification: PBT_POWERINFOCHANGEn"));
   break;
  }
  default:
   break;
  }
 }
 delete[] ppb;
}

5. Build the application and rebuild the run-time image.

6. Start the run-time image.

7. You generate user activity by moving the mouse cursor. After five seconds of inactivity, Power Manager should notify the application, as illustrated in Figure 3-12.

Figure 3-12 Received Power Management notifications

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