Transferring Content from the Device to a PC

One common operation accomplished by a WPD application is the transfer of content from a connected device to the PC.

Content transfers are accomplished using the interfaces described in the following table.

The TransferContentFromDevice function in the sample application's ContentTransfer.cpp module demonstrates how an application could transfer contact information from a connected device to a PC.

The first task accomplished by the TransferContentFromDevice function is to prompt the user to enter an object identifier for the parent object on the device (under which the content will be transferred).

HRESULT                            hr                   = S_OK;
WCHAR                              szSelection[81]      = {0};
CComPtr<IPortableDeviceContent>    pContent;
CComPtr<IPortableDeviceResources>  pResources;
CComPtr<IPortableDeviceProperties> pProperties;
CComPtr<IStream>                   pObjectDataStream;
CComPtr<IStream>                   pFinalFileStream;
DWORD                              cbOptimalTransferSize = 0;
CAtlStringW                        strOriginalFileName;

if (pDevice == NULL)
{
    printf("! A NULL IPortableDevice interface pointer was received\n");
    return;
}


// Prompt user to enter an object identifier on the device to transfer.
printf("Enter the identifer of the object you wish to transfer.\n>");
hr = StringCbGetsW(szSelection,sizeof(szSelection));
if (FAILED(hr))
{
    printf("An invalid object identifier was specified, aborting content transfer\n");
}

The next step is the retrieval of an IPortableDeviceContent object that the sample uses to access the content-specific methods.

if (SUCCEEDED(hr))
{
    hr = pDevice->Content(&pContent);
    if (FAILED(hr))
    {
        printf("! Failed to get IPortableDeviceContent from IPortableDevice, hr = 0x%lx\n",hr);
    }
}

The next step is the retrieval of an IPortableDeviceResources object that the sample uses to access the resource-specific methods.

if (SUCCEEDED(hr))
{
    hr = pContent->Transfer(&pResources);
    if (FAILED(hr))
    {
        printf("! Failed to get IPortableDeviceResources from IPortableDeviceContent, hr = 0x%lx\n",hr);
    }
}

The next step is the retrieval of an IStream object that the sample uses to read the data it is transferring from the device.

if (SUCCEEDED(hr))
{
    hr = pResources->GetStream(szSelection,             // Identifier of the object we want to transfer
                               WPD_RESOURCE_DEFAULT,    // We are transferring the default resource (which is the entire object's data)
                               STGM_READ,               // Opening a stream in READ mode, because we are reading data from the device.
                               &cbOptimalTransferSize,  // Driver supplied optimal transfer size
                               &pObjectDataStream);
    if (FAILED(hr))
    {
        printf("! Failed to get IStream (representing object data on the device) from IPortableDeviceResources, hr = 0x%lx\n",hr);
    }
}

The next step is the retrieval of the object's file name on the device. This string is used to create the corresponding file name on the PC. If the object does not have a file name on the device, the object's identifier is converted to a string and used to create the destination file name.

if (SUCCEEDED(hr))
{
    hr = pContent->Properties(&pProperties);
    if (SUCCEEDED(hr))
    {
        hr = GetStringValue(pProperties,
                            szSelection,
                            WPD_OBJECT_ORIGINAL_FILE_NAME,
                            strOriginalFileName);
        if (FAILED(hr))
        {
            printf("! Failed to read WPD_OBJECT_ORIGINAL_FILE_NAME on object '%ws', hr = 0x%lx\n", szSelection, hr);
            strOriginalFileName.Format(L"%ws.data", szSelection);
            printf("* Creating a filename '%ws' as a default.\n", (PWSTR)strOriginalFileName.GetString());
            // Set the HRESULT to S_OK, so we can continue with our newly generated
            // temporary file name.
            hr = S_OK;
        }
    }
    else
    {
        printf("! Failed to get IPortableDeviceProperties from IPortableDeviceContent, hr = 0x%lx\n", hr);
    }
}

After this, the sample creates a destination IStream object.

if (SUCCEEDED(hr))
{
    hr = SHCreateStreamOnFile(strOriginalFileName, STGM_CREATE|STGM_WRITE, &pFinalFileStream);
    if (FAILED(hr))
    {
        printf("! Failed to create a temporary file named (%ws) to transfer object (%ws), hr = 0x%lx\n",(PWSTR)strOriginalFileName.GetString(), szSelection, hr);
    }
}

Finally, the source IStream object is copied to the destination on the PC.

if (SUCCEEDED(hr))
{
    DWORD cbTotalBytesWritten = 0;

    // Since we have IStream-compatible interfaces, call our helper function
    // that copies the contents of a source stream into a destination stream.
    hr = StreamCopy(pFinalFileStream,       // Destination (The Final File to transfer to)
                    pObjectDataStream,      // Source (The Object's data to transfer from)
                    cbOptimalTransferSize,  // The driver specified optimal transfer buffer size
                    &cbTotalBytesWritten);  // The total number of bytes transferred from device to the finished file
    if (FAILED(hr))
    {
        printf("! Failed to transfer object from device, hr = 0x%lx\n",hr);
    }
    else
    {
        printf("* Transferred object '%ws' to '%ws'.\n", szSelection, (PWSTR)strOriginalFileName.GetString());
    }
}

Related topics

IPortableDevice Interface

IPortableDeviceContent Interface

IPortableDeviceValues Interface

Programming Guide