将图像或音乐文件传输到设备

项目
06/13/2023

应用程序完成的最常见操作之一是将内容传输到连接的设备。

内容传输是使用下表中所述的接口完成的。

接口	说明
IPortableDeviceContent 接口	提供对特定于内容的方法的访问。
IPortableDeviceDataStream 接口	在将内容写入设备时使用。
IPortableDeviceValues 接口	用于检索描述内容的属性。
IStream 接口	用于简化内容读取和写入设备。

TransferContentToDevice示例应用程序的 ContentTransfer.cpp 模块中的函数演示了应用程序如何将内容从电脑传输到连接的设备。在此特定示例中，传输的内容可以是包含图像、音乐或联系信息的文件。

函数完成 TransferContentToDevice 的第一个任务是提示用户输入对象标识符，用于标识要传输的对象。

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");
}

函数完成TransferContentToDevice的第二个任务是通过调用 IPortableDevice：：Content 方法创建 IPortableDeviceContent 对象。

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

函数完成 TransferContentToDevice 的下一个任务是创建 FileOpen 对话框，用户可以使用该对话框指定要传输的文件的位置和名称。

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;
    }
}

函数 TransferContentToDevice 将筛选器字符串 (wszFileTypeFilter) 传递给 GetOpenFileName 方法，该方法确定用户可以选择的文件类型。有关 DoMenu 示例允许的三个不同筛选器的示例，请参阅 WpdApiSample.cpp 模块中的函数。

用户标识要传输到设备的特定文件后，函数将 TransferContentToDevice 该文件作为 IStream 对象打开，并检索完成传输所需的属性。

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);
    }
}

通过调用对 IStream 对象操作的GetRequiredPropertiesForContentType helper-function 来检索所需的属性。帮助 GetRequiredPropertiesForContentType 程序函数创建 IPortableDeviceValues 对象，检索以下列表中的属性，并将其添加到此对象。

父对象标识符
流大小（以字节为单位）
内容文件名
内容名称 (没有扩展名的文件名)
内容类型 (图像、音频或联系人)
内容格式 (JFIF、WMA 或 vCard2)

示例应用程序使用检索到的属性在设备上创建新内容。此操作分三个阶段完成：

应用程序调用 IPortableDeviceContent：：CreateObjectWithPropertiesAndData 方法在设备上创建新的 IStream 对象。
应用程序使用此对象从 WPD 驱动程序获取 IPortableDeviceDataStream 对象。
应用程序使用新的 IPortableDeviceDataStream 对象通过 StreamCopy 帮助程序函数) 将内容写入设备 (。帮助程序函数将数据从源文件写入 IPortableDeviceContent：：CreateObjectWithPropertiesAndData 返回的流。
应用程序通过在目标流上调用 Commit 方法来完成操作。

// 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 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 接口
IPortableDeviceContent 接口
IPortableDeviceDataStream 接口
IPortableDeviceValues 接口
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