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Enabling Notifications

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Windows Media Device Manager declares four interfaces that an application can implement in a COM class to receive event notifications. These interfaces fall into two groups, as shown in the following table.

Interfaces Description
IWMDMNotification Notifies the application when devices or storage media are connected or disconnected.
IWMDMProgress

IWMDMProgress2

IWMDMProgress3

 A very simple notification system to alert an application about the progress of any event. The application is not required to take any actions in response to these messages.

IWMDMNotification

IWMDMNotification alerts the application when Plug and Play devices are connected or disconnected from the computer, as well as when Plug and Play storage media (such as flash cards) are inserted or removed from the device. These notifications can help the application update its user interface to reflect changes.

In order to receive these notifications, your application must register to receive them using the Platform SDK IConnectionPointContainer and IConnectionPoint interfaces. Your application should register to receive events when it starts up, and unregister when it closes. Follow these steps to register to receive these notifications.

  1. Query the main IWMDeviceManager interface you received when you authenticated your application for IConnectionPointContainer.
  2. Call IConnectionPointContainer::FindConnectionPoint to retrieve a container connection point for IWMDMNotification interfaces.
  3. Register to receive events by calling IConnectionPoint::Advise. Pass in the class that implements IWMDMNotification, and retrieve a cookie, a unique ID that identifies your connection point. This must be stored, and used later to unregister for event notifications.

The following C++ code demonstrates how you can register to receive notifications from IWMDMNotification.

HRESULT CWMDMController::RegisterForNotifications()
{
    HRESULT hr = S_OK;
    CComPtr<IConnectionPointContainer> pConxnPointCont;
    CComPtr<IConnectionPoint> pIConnPoint;

    // Get the IConnectionPointContainer interface from IWMDeviceManager.
    if (SUCCEEDED (hr = m_IWMDMDeviceMgr->QueryInterface(IID_IConnectionPointContainer, (void**) & pConxnPointCont)))
    {
        // Get a connection point from the container.
        if (SUCCEEDED (hr = pConxnPointCont->FindConnectionPoint(IID_IWMDMNotification, &pIConnPoint)))
        {
            // Add ourselves as a callback handler for the connection point.
            // If we succeeded, indicate that by storing the connection point ID.
            DWORD dwCookie;
            if (SUCCEEDED (hr = pIConnPoint->Advise((IUnknown*)((IWMDMNotification*)this), &dwCookie)))
            {
                m_dwNotificationCookie = dwCookie;
            }
        }
    }

    return hr;
}

When your application closes, you must unregister with IConnectionPoint to indicate that it should no longer send you notifications. Follow these steps to unregister for notifications:

  1. Query the main IWMDeviceManager interface for IConnectionPointContainer.
  2. Get a connection point for IWMDMNotification interfaces.
  3. Unregister your application for event notifications by calling IConnectionPoint::Unadvise, passing in the unique ID received when you registered to receive events.

The following C++ code shows how to unregister for IWMDMNotification events when your application closes.

HRESULT CWMDMController::UnregisterForNotifications()
{
    HRESULT hr = S_FALSE;

    // On class initialization, we initialized the handle to -1 as a flag 
    // to indicate we had not yet registered for notifications. If registration 
    // never happened, don't bother to unregister.
    if (-1 != m_dwNotificationCookie)
    {
        CComPtr<IConnectionPointContainer> pConxnPointCont;
        CComPtr<IConnectionPoint> pIConnPoint;

        // Get the connection point container from IWMDeviceManager. 
        if (SUCCEEDED (hr = 
           m_IWMDMDeviceMgr->QueryInterface(IID_IConnectionPointContainer,
           (void**) & pConxnPointCont)))
        {
            // Get a connection point from the container.
            if (SUCCEEDED (hr = pConxnPointCont->FindConnectionPoint(IID_IWMDMNotification, &pIConnPoint)))
            {
                // Remove ourselves as a callback from the connection point.
                // If successful, reset the ID to a flag value.
                if (SUCCEEDED (hr = 
                    pIConnPoint->Unadvise(m_dwNotificationCookie)))
                {
                    m_dwNotificationCookie = -1;
                    hr = S_OK;
                }
            }
        }
    }

    return hr;
}

Using IWMDMProgress

Windows Media Device Manager can send your application status messages when specific actions, such as content transfer, secure clock acquisition, and encountering DRM file information, occur. Your application can use these messages to monitor the status of the event or cancel an event. To use this interface, implement IWMDMProgress, IWMDMProgress2, or IWMDMProgress3, and pass it in as a parameter to a method that will accept a progress message. Note that IWMDMProgress3 is the superior interface because it provides an identification GUID that specifies what action is being tracked. The following application methods accept a progress interface (the corresponding service provider methods should be able to send notifications to a submitted interface):

IWMDMStorageControl::Delete

IWMDMStorageControl::Insert

IWMDMStorageControl::Move

IWMDMStorageControl::Read

IWMDMStorageControl::Rename

IWMDMStorageControl2::Insert2

IWMDMStorageControl3::Insert3

IWMDMStorageGlobals::Initialize

IWMDRMDeviceApp::AcquireDeviceData

Examples of passing an interface into a method are given in the documentation for these methods. For examples of implementing the callback interfaces, see the documentation for the methods of IWMDMProgress, IWMDMProgress2, or IWMDMProgress3.

See Also