Enumerating Devices

After authenticating an application, you can begin to enumerate the devices detected by Windows Media Device Manager. Enumeration is done by using an enumeration interface, IWMDMEnumDevice, obtained by using either IWMDeviceManager2::EnumDevices2 or IWMDeviceManager::EnumDevices. If supported, use the EnumDevices2 method, because the earlier version only returned legacy interfaces on devices, whereas the new version returns both the legacy and the new interfaces.

Before obtaining an enumerator, you should decide what enumeration view to use. Some devices expose each storage as a different device. For example, two flash memory cards on a device will enumerate as if they were separate devices. You can specify that all storages on a device are enumerated together as a single device. You can set this preference only once in your application; if you want to change it, you must shut down the application and restart it. However, note that legacy devices will sometimes ignore a request to enumerate separate device storages as a single device, and continue to enumerate them separately.

The following steps show how to enumerate connected devices:

  1. Set the device enumeration preference using IWMDeviceManager3::SetDeviceEnumPreference. If this method is not called, the default method is to show storages as separate devices. To determine whether individual "devices" are actually storages on the same device, call IWMDMDevice2::GetCanonicalName; storages from the same device will return identical values, except for the final digit after the last "$" sign.
  2. Query for IWMDeviceManager or IWMDeviceManager2, and then call IWMDeviceManager2::EnumDevices2 to obtain the device enumerator interface, IWMDMEnumDevice. (If supported, use EnumDevices2, which is more efficient, as the earlier version may not return MTP devices).
  3. Call the IWMDMEnumDevices::Next method to retrieve one or more devices at a time. Continue to call this method until the method returns S_FALSE or an error message. If retrieving only one device at a time, you do not need to allocate an array to hold the devices.

Because users can attach or remove devices from the computer while your application is running, it is a good idea to implement notification of device connection or removal. This is done by implementing the IWMDMNotification interface and registering it. For more information on this, see Enabling Notifications.

The following C++ code enumerates devices and requests information about each device.



HRESULT CWMDMController::EnumDevices()
{
    HRESULT hr = S_OK;

    // Change behavior to show devices as one object, not each storage as a device.
    // This can be called only once for each instance of this application.
    CComQIPtr<IWMDeviceManager3>pDevMgr3(m_IWMDMDeviceMgr);
    hr = pDevMgr3->SetDeviceEnumPreference(DO_NOT_VIRTUALIZE_STORAGES_AS_DEVICES);
    
    // Get number of attached devices.
    DWORD iDevices = 0;
    hr = m_IWMDMDeviceMgr->GetDeviceCount(&iDevices);
    if (hr == S_OK)
    {
        // TODO: Display count of devices.
    }

    //
    // Get a device enumerator to enumerate devices.
    //
    CComPtr<IWMDeviceManager2> pDevMgr2;
    hr = m_IWMDMDeviceMgr->QueryInterface (__uuidof(IWMDeviceManager2), (void**) &pDevMgr2);
    if (hr == S_OK)
    {
        // TODO: Display message indicating that application obtained IWMDeviceManager2.
    }
    else
    {
        // TODO: Display message indicating that we couldn't 
        // get IWMDeviceManager2 in EnumDevices.
        return hr;
    }
   CComPtr<IWMDMEnumDevice> pEnumDevice;
   hr = pDevMgr2->EnumDevices2(&pEnumDevice);
    if (hr != S_OK)
    {
        // TODO: Display messaging indicating that an error occurred 
        // in calling EnumDevices2.
        return hr;
    }

    // Length of all the strings we'll send in. 
    const UINT MAX_CHARS = 100;

    // Iterate through devices.
    while(TRUE)
    {
        // Get a device handle.
        IWMDMDevice *pIWMDMDevice;
        ULONG ulFetched = 0;
        hr = pEnumDevice->Next(1, &pIWMDMDevice, &ulFetched);
        if ((hr != S_OK) || (ulFetched != 1))
        {
            break;
        }
        
        // Get a display icon for the device.
        ULONG deviceIcon = 0;
        hr = pIWMDMDevice->GetDeviceIcon(&deviceIcon);

        // Print the device manufacturer.
        WCHAR manufacturer[MAX_CHARS];
        hr = pIWMDMDevice->GetManufacturer((LPWSTR)&manufacturer, MAX_CHARS);
        if (hr == S_OK)
        {
            // TODO: Display manufacturer name.
        }

        // Get the device name.
        WCHAR name[MAX_CHARS];
        hr = pIWMDMDevice->GetName((LPWSTR)&name, MAX_CHARS);
        if (hr == S_OK)
        {
            // TODO: Display name.
        }

        // TODO: Get other device information if wanted.

        // Obtain an IWMDMDevice2 interface and call some methods.
        CComQIPtr<IWMDMDevice2> pIWMDMDevice2(pIWMDMDevice);
        if (pIWMDMDevice2 != NULL)
        {
            // Get the canonical name.
            WCHAR canonicalName[MAX_CHARS];
            hr = pIWMDMDevice2->GetCanonicalName(canonicalName, MAX_CHARS);
            if (hr == S_OK)
            {
                // TODO: Display canonical name.
            }
        }

        // Obtain an IWMDMDevice3 interface and call some methods.
        CComQIPtr<IWMDMDevice3>pIWMDMDevice3(pIWMDMDevice);
        if (pIWMDMDevice3 != NULL)
        {
            // Find out what protocol is being used.
            PROPVARIANT val;
            PropVariantInit(&val);
            hr = pIWMDMDevice3->GetProperty(g_wszWMDMDeviceProtocol, &val);

            if (hr == S_OK)
            {
                if (*val.puuid == WMDM_DEVICE_PROTOCOL_RAPI)
                {
                    // TODO: Display message indicating device is a RAPI device.
                }
                else if (*val.puuid == WMDM_DEVICE_PROTOCOL_MTP)
                {
                    / /TODO: Display message indicating device is an MTP device.
                }
                else if (*val.puuid == WMDM_DEVICE_PROTOCOL_MSC)
                {
                    // TODO: Display message indicating device is an MSC device.
                }
                else
                {
                    // TODO: Display message indicating that the 
                    // application encountered an unknown protocol.
                }
                PropVariantClear(&val);
            }
        }

        // Examine the device capabilities. You could use some of these
        // to enable or disable the application's UI elements.
        CComQIPtr<IWMDMDeviceControl> pDeviceControl(pIWMDMDevice);
        if (pDeviceControl != NULL)
        {
            DWORD caps = 0;
            hr = pDeviceControl->GetCapabilities(&caps);
            if (caps & WMDM_DEVICECAP_CANPLAY)
            {
                // TODO: Display message indicating that the media 
                // device can play MP3 audio.
            }
            // TODO: Test for other capabilities here.
        }
    } // Get the next device.
    return hr;
}


Related topics

Creating a Windows Media Device Manager Application

 

 

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