Transferring an Image or Music File to the Device

One of the most common operations accomplished by an application is the transfer of content to a connected device.

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

Interface Description
IPortableDeviceContent Interface Provides access to the content-specific methods.
IPortableDeviceDataStream Interface Used when writing the content to the device.
IPortableDeviceValues Interface Used to retrieve properties that describe the content.
IStream Interface Used to simplify reading of content and writing to the device.

 

The TransferContentToDevice function in the sample application's ContentTransfer.cpp module demonstrates how an application could transfer content from a PC to a connected device. In this particular sample, the transferred content can be a file containing an image, music, or contact information.

The first task accomplished by the TransferContentToDevice function is to prompt the user to enter an object identifier, which identifies the object to be transferred.

HRESULT                             hr = S_OK;
WCHAR                               szSelection[81]        = {0};
WCHAR                               szFilePath[MAX_PATH]   = {0};
DWORD                               cbOptimalTransferSize   = 0;
CComPtr<IStream>                    pFileStream;
CComPtr<IPortableDeviceDataStream>  pFinalObjectDataStream;
CComPtr<IPortableDeviceValues>      pFinalObjectProperties;
CComPtr<IPortableDeviceContent>     pContent;
CComPtr<IStream>                    pTempStream;  // Temporary IStream which we use to QI for IPortableDeviceDataStream

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

The second task accomplished by the TransferContentToDevice function is to create an IPortableDeviceContent object by calling the IPortableDevice::Content method.

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

The next task accomplished by the TransferContentToDevice function is the creation of a FileOpen dialog with which the user can specify the location and name of the file to be transferred.

if (SUCCEEDED(hr))
{
    OPENFILENAME OpenFileNameInfo   = {0};

    OpenFileNameInfo.lStructSize    = sizeof(OPENFILENAME);
    OpenFileNameInfo.hwndOwner      = NULL;
    OpenFileNameInfo.lpstrFile      = szFilePath;
    OpenFileNameInfo.nMaxFile       = ARRAYSIZE(szFilePath);
    OpenFileNameInfo.lpstrFilter    = pszFileTypeFilter;
    OpenFileNameInfo.nFilterIndex   = 1;
    OpenFileNameInfo.Flags          = OFN_PATHMUSTEXIST | OFN_FILEMUSTEXIST;
    OpenFileNameInfo.lpstrDefExt    = pszDefaultFileExtension;

    if (GetOpenFileName(&OpenFileNameInfo) == FALSE)
    {
        printf("The transfer operation was canceled.\n");
        hr = E_ABORT;
    }
}

The TransferContentToDevice function passes a filter string (wszFileTypeFilter) to the GetOpenFileName method, which determines the type of files that the user can choose. Refer to the DoMenu function in the WpdApiSample.cpp module for examples of the three different filters allowed by the sample.

After the user identifies a particular file for transfer to the device, the TransferContentToDevice function opens that file as an IStream object and retrieves properties that are required to complete the transfer.

if (SUCCEEDED(hr))
{
    // Open the selected file as an IStream.  This will simplify reading the
    // data and writing to the device.
    hr = SHCreateStreamOnFile(szFilePath, STGM_READ, &pFileStream);
    if (SUCCEEDED(hr))
    {
        // Get the required properties needed to properly describe the data being
        // transferred to the device.
        hr = GetRequiredPropertiesForContentType(guidContentType,           // Content type of the data
                                                 szSelection,              // Parent to transfer the data under
                                                 szFilePath,               // Full file path to the data file
                                                 pFileStream,               // Open IStream that contains the data
                                                 &pFinalObjectProperties);  // Returned properties describing the data
        if (FAILED(hr))
        {
            printf("! Failed to get required properties needed to transfer a file to the device, hr = 0x%lx\n", hr);
        }
    }

    if (FAILED(hr))
    {
        printf("! Failed to open file named (%ws) to transfer to device, hr = 0x%lx\n",szFilePath, hr);
    }
}

The required properties are retrieved by calling theGetRequiredPropertiesForContentType helper-function, which operates on the IStream object. The GetRequiredPropertiesForContentType helper-function creates an IPortableDeviceValues object, retrieves the properties in the following list, and adds them to this object.

  • Parent-object identifier
  • Stream size in bytes
  • Content file name
  • Content name (the file name without the extension)
  • Content type (image, audio, or contact)
  • Content format (JFIF, WMA, or vCard2)

The sample application uses the retrieved properties to create the new content on the device. This is done in three phases:

  1. The application calls IPortableDeviceContent::CreateObjectWithPropertiesAndData method to create a new IStream object on the device.
  2. The application uses this object to obtain an IPortableDeviceDataStream object from the WPD driver.
  3. The application uses the new IPortableDeviceDataStream object to write the content to the device (via the StreamCopy helper function). The helper function writes the data from the source file to the stream returned by IPortableDeviceContent::CreateObjectWithPropertiesAndData.
  4. The application completes the operation by calling the Commit method on the destination stream.
// 4) Transfer for the content to the device
if (SUCCEEDED(hr))
{
    hr = pContent->CreateObjectWithPropertiesAndData(pFinalObjectProperties,    // Properties describing the object data
                                                     &pTempStream,              // Returned object data stream (to transfer the data to)
                                                     &cbOptimalTransferSize,    // Returned optimal buffer size to use during transfer
                                                     NULL);

    // Once we have a the IStream returned from CreateObjectWithPropertiesAndData,
    // QI for IPortableDeviceDataStream so we can use the additional methods
    // to get more information about the object (i.e. The newly created object
    // identifier on the device)
    if (SUCCEEDED(hr))
    {
        hr = pTempStream->QueryInterface(IID_PPV_ARGS(&pFinalObjectDataStream));
        if (FAILED(hr))
        {
            printf("! Failed to QueryInterface for IPortableDeviceDataStream, hr = 0x%lx\n",hr);
        }
    }

    // Since we have IStream-compatible interfaces, call our helper function
    // that copies the contents of a source stream into a destination stream.
    if (SUCCEEDED(hr))
    {
        DWORD cbTotalBytesWritten = 0;

        hr = StreamCopy(pFinalObjectDataStream, // Destination (The Object to transfer to)
                        pFileStream,            // Source (The File data to transfer from)
                        cbOptimalTransferSize,  // The driver specified optimal transfer buffer size
                        &cbTotalBytesWritten);  // The total number of bytes transferred from file to the device
        if (FAILED(hr))
        {
            printf("! Failed to transfer object to device, hr = 0x%lx\n",hr);
        }
    }
    else
    {
        printf("! Failed to get IStream (representing destination object data on the device) from IPortableDeviceContent, hr = 0x%lx\n",hr);
    }

    // After transferring content to the device, the client is responsible for letting the
    // driver know that the transfer is complete by calling the Commit() method
    // on the IPortableDeviceDataStream interface.
    if (SUCCEEDED(hr))
    {
        hr = pFinalObjectDataStream->Commit(0);
        if (FAILED(hr))
        {
            printf("! Failed to commit object to device, hr = 0x%lx\n",hr);
        }
    }

    // Some clients may want to know the object identifier of the newly created
    // object.  This is done by calling GetObjectID() method on the
    // IPortableDeviceDataStream interface.
    if (SUCCEEDED(hr))
    {
        PWSTR pszNewlyCreatedObject = NULL;
        hr = pFinalObjectDataStream->GetObjectID(&pszNewlyCreatedObject);
        if (SUCCEEDED(hr))
        {
            printf("The file '%ws' was transferred to the device.\nThe newly created object's ID is '%ws'\n",szFilePath ,pszNewlyCreatedObject);
        }

        if (FAILED(hr))
        {
            printf("! Failed to get the newly transferred object's identifier from the device, hr = 0x%lx\n",hr);
        }

        // Free the object identifier string returned from the GetObjectID() method.
        CoTaskMemFree(pszNewlyCreatedObject);
        pszNewlyCreatedObject = NULL;
    }
}

IPortableDevice Interface

IPortableDeviceContent Interface

IPortableDeviceDataStream Interface

IPortableDeviceValues Interface

Programming Guide