Книга: Microsoft Windows Embedded CE 6.0 Exam Preparation Kit

Notification Interface

Notification Interface

The notification interface provides two functions that applications can use to register and deregister for power notifications through message queues, as listed in Table 3-17. It is important to note that power notifications are multicast messages, which means that Power Manager sends these notification messages only to registered processes. In this way, power management-enabled applications can seamlessly coexist on Windows Embedded CE with applications that do not implement the Power Management API.

Table 3-17 Power Management notification interface

The following sample code illustrates how to use power notifications:

// Size of a POWER_BROADCAST message.
DWORD cbPowerMsgSize =
 sizeof POWER_BROADCAST + (MAX_PATH * sizeof TCHAR);
// Initialize a 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 ERROR;
}
// Request power notifications.
HANDLE hPowerNotifications = RequestPowerNotifications(hPowerMsgQ,
 PBT_TRANSITION | PBT_RESUME | PBT_POWERINFOCHANGE);
// Wait for a power notification or for the app to exit.
while(WaitForSingleObject(hPowerMsgQ, FALSE, 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)) {
  // Perform action according to the message type.
 }
}

Оглавление книги