Establishing a Connection

Once the user selects a device, the ChooseDevice function, in turn, calls the IPortableDevice::Open method to establish a connection between the application and the device. The IPortableDevice::Open method takes two arguments:

• A pointer to a null-terminated string that specifies the Plug and Play name of the device. (This string is retrieved by calling the IPortableDeviceManager::GetDevices method.)
• A pointer to an IPortableDeviceValues interface that specifies client information for the application.

// CoCreate the IPortableDevice interface and call Open() with
// the chosen PnPDeviceID string.
hr = CoCreateInstance(CLSID_PortableDeviceFTM,
                      NULL,
                      CLSCTX_INPROC_SERVER,
                      IID_PPV_ARGS(ppDevice));
if (SUCCEEDED(hr))
{
    hr = (*ppDevice)->Open(pPnpDeviceIDs[uiCurrentDevice], pClientInformation);
    if (FAILED(hr))
    {
        if (hr == E_ACCESSDENIED)
        {
            printf("Failed to Open the device for Read Write access, will open it for Read-only access instead\n");
            pClientInformation->SetUnsignedIntegerValue(WPD_CLIENT_DESIRED_ACCESS, GENERIC_READ);
            hr = (*ppDevice)->Open(pPnpDeviceIDs[uiCurrentDevice], pClientInformation);
            if (FAILED(hr))
            {
                printf("! Failed to Open the device, hr = 0x%lx\n",hr);
                // Release the IPortableDevice interface, because we cannot proceed
                // with an unopen device.
                (*ppDevice)->Release();
                *ppDevice = NULL;
            }
        }
        else
        {
            printf("! Failed to Open the device, hr = 0x%lx\n",hr);
            // Release the IPortableDevice interface, because we cannot proceed
            // with an unopen device.
            (*ppDevice)->Release();
            *ppDevice = NULL;
        }
    }
}
else
{
    printf("! Failed to CoCreateInstance CLSID_PortableDeviceFTM, hr = 0x%lx\n",hr);
}

For Windows 7, IPortableDevice supports two CLSIDs for CoCreateInstance. CLSID_PortableDevice returns an IPortableDevice pointer that does not aggregate the free-threaded marshaler; CLSID_PortableDeviceFTM is a new CLSID that returns an IPortableDevice pointer that aggregates the free-threaded marshaler. Both pointers support the same functionality otherwise.

Applications that live in Single Threaded Apartments should use CLSID_PortableDeviceFTM as this eliminates the overhead of interface pointer marshaling. CLSID_PortableDevice is still supported for legacy applications.

Related topics

Selecting a Device