设置多个对象的属性
某些设备驱动程序支持在单个函数调用中为多个对象设置属性，这称为批量写入。 应用程序可以使用下表中所述的接口执行批量写入。
| 接口 | 说明 |
|---|---|
| IPortableDeviceContent 接口 | 提供对特定于内容的方法的访问。 |
| IPortableDeviceProperties 接口 | 提供对特定于属性的方法的访问。 |
| IPortableDevicePropertiesBulk 接口 | 支持大容量写入操作。 |
| IPortableDevicePropVariantCollection 接口 | 用于存储批量操作的对象标识符。 |
| IPortableDeviceValuesCollection 接口 | 用于标识要写入的属性。 |
WriteContentPropertiesBulk示例应用程序的 ContentProperties.cpp 模块中的 函数演示了大容量写入操作。
此示例中完成的第一个任务是确定给定的驱动程序是否支持批量操作。 这是通过在 IPortableDeviceProperties 对象上调用 QueryInterface 并检查 是否存在 IPortableDevicePropertiesBulk 来实现的。
HRESULT hr = S_OK;
GUID guidContext = GUID_NULL;
CSetBulkValuesCallback* pCallback = NULL;
CComPtr<IPortableDeviceProperties> pProperties;
CComPtr<IPortableDevicePropertiesBulk> pPropertiesBulk;
CComPtr<IPortableDeviceValues> pObjectProperties;
CComPtr<IPortableDeviceContent> pContent;
CComPtr<IPortableDeviceValuesCollection> pPropertiesToWrite;
CComPtr<IPortableDevicePropVariantCollection> pObjectIDs;
DWORD cObjectIDs = 0;
if (SUCCEEDED(hr))
{
hr = pDevice->Content(&pContent);
if (FAILED(hr))
{
printf("! Failed to get IPortableDeviceContent from IPortableDevice, hr = 0x%lx\n",hr);
}
}
if (SUCCEEDED(hr))
{
hr = pContent->Properties(&pProperties);
if (FAILED(hr))
{
printf("! Failed to get IPortableDeviceProperties from IPortableDevice, hr = 0x%lx\n",hr);
}
}
if (SUCCEEDED(hr))
{
hr = pProperties->QueryInterface(IID_PPV_ARGS(&pPropertiesBulk));
if (FAILED(hr))
{
printf("This driver does not support BULK property operations.\n");
}
}
下一个任务需要创建 IPortableDeviceValuesCollection 对象。 这是包含示例将写入的属性值的 对象。
HRESULT hr = S_OK;
GUID guidContext = GUID_NULL;
CSetBulkValuesCallback* pCallback = NULL;
CComPtr<IPortableDeviceProperties> pProperties;
CComPtr<IPortableDevicePropertiesBulk> pPropertiesBulk;
CComPtr<IPortableDeviceValues> pObjectProperties;
CComPtr<IPortableDeviceContent> pContent;
CComPtr<IPortableDeviceValuesCollection> pPropertiesToWrite;
CComPtr<IPortableDevicePropVariantCollection> pObjectIDs;
DWORD cObjectIDs = 0;
if (SUCCEEDED(hr))
{
hr = CoCreateInstance(CLSID_PortableDeviceValuesCollection,
NULL,
CLSCTX_INPROC_SERVER,
IID_IPortableDeviceValuesCollection,
(VOID**) &pPropertiesToWrite);
if (FAILED(hr))
{
printf("! Failed to CoCreate IPortableDeviceValuesCollection for bulk property values, hr = 0x%lx\n", hr);
}
}
在此之后，该示例将创建 IPortableDevicePropertiesBulkCallback 接口的实例。 应用程序将使用此接口中的方法跟踪异步大容量写入操作的进度。
HRESULT hr = S_OK;
GUID guidContext = GUID_NULL;
CSetBulkValuesCallback* pCallback = NULL;
CComPtr<IPortableDeviceProperties> pProperties;
CComPtr<IPortableDevicePropertiesBulk> pPropertiesBulk;
CComPtr<IPortableDeviceValues> pObjectProperties;
CComPtr<IPortableDeviceContent> pContent;
CComPtr<IPortableDeviceValuesCollection> pPropertiesToWrite;
CComPtr<IPortableDevicePropVariantCollection> pObjectIDs;
DWORD cObjectIDs = 0;
if (SUCCEEDED(hr))
{
pCallback = new CSetBulkValuesCallback();
if (pCallback == NULL)
{
hr = E_OUTOFMEMORY;
printf("! Failed to allocate CSetBulkValuesCallback, hr = 0x%lx\n", hr);
}
}
示例应用程序调用的下一个函数是 CreateIPortableDevicePropVariantCollectionWithAllObjectIDs 帮助程序函数。 此函数以递归方式枚举给定设备上的所有对象，并返回 一个 IPortableDevicePropVariantCollection 接口 ，该接口包含它找到的每个对象的标识符。 此函数在模块 ContentEnumeration.cpp 中定义。
// 7) Call our helper function CreateIPortableDevicePropVariantCollectionWithAllObjectIDs
// to enumerate and create an IPortableDevicePropVariantCollection with the object
// identifiers needed to perform the bulk operation on.
if (SUCCEEDED(hr))
{
hr = CreateIPortableDevicePropVariantCollectionWithAllObjectIDs(pDevice,
pContent,
&pObjectIDs);
}
IPortableDevicePropVariantCollection 对象包含同一 VARTYPE 的索引 PROPVARIANT 值的集合。 在这种情况下，这些值包含设备上找到的每个对象的给定对象标识符。
对象标识符及其各自的名称属性存储在 IPortableDeviceValuesCollection 对象中。 组织名称属性，以便为第一个对象分配名称属性“NewName0”，为第二个对象分配名称属性“NewName1”，依此而论。
以下示例的以下摘录演示了如何使用对象标识符和新名称字符串初始化 IPortableDeviceValuesCollection 对象。
HRESULT hr = S_OK;
GUID guidContext = GUID_NULL;
CSetBulkValuesCallback* pCallback = NULL;
CComPtr<IPortableDeviceProperties> pProperties;
CComPtr<IPortableDevicePropertiesBulk> pPropertiesBulk;
CComPtr<IPortableDeviceValues> pObjectProperties;
CComPtr<IPortableDeviceContent> pContent;
CComPtr<IPortableDeviceValuesCollection> pPropertiesToWrite;
CComPtr<IPortableDevicePropVariantCollection> pObjectIDs;
DWORD cObjectIDs = 0;
if (SUCCEEDED(hr))
{
hr = pObjectIDs->GetCount(&cObjectIDs);
if (FAILED(hr))
{
printf("! Failed to get number of objectIDs from IPortableDevicePropVariantCollection, hr = 0x%lx\n", hr);
}
}
if (SUCCEEDED(hr))
{
for(DWORD dwIndex = 0; (dwIndex < cObjectIDs) && (hr == S_OK); dwIndex++)
{
CComPtr<IPortableDeviceValues> pValues;
PROPVARIANT pv = {0};
PropVariantInit(&pv);
hr = CoCreateInstance(CLSID_PortableDeviceValues,
NULL,
CLSCTX_INPROC_SERVER,
IID_IPortableDeviceValues,
(VOID**) &pValues);
if (FAILED(hr))
{
printf("! Failed to CoCreate CLSID_PortableDeviceValues, hr = 0x%lx\n", hr);
}
// Get the Object ID whose properties we will set
if (hr == S_OK)
{
hr = pObjectIDs->GetAt(dwIndex, &pv);
if (FAILED(hr))
{
printf("! Failed to get next Object ID from list, hr = 0x%lx\n", hr);
}
}
// Save them into the IPortableDeviceValues so the driver knows which object this proeprty set belongs to
if (hr == S_OK)
{
hr = pValues->SetStringValue(WPD_OBJECT_ID, pv.pwszVal);
if (FAILED(hr))
{
printf("! Failed to set WPD_OBJECT_ID, hr = 0x%lx\n", hr);
}
}
// Set the new values. In this sample, we attempt to set the name property.
if (hr == S_OK)
{
CAtlStringW strValue;
strValue.Format(L"NewName%d", dwIndex);
hr = pValues->SetStringValue(WPD_OBJECT_NAME, strValue.GetString());
if (FAILED(hr))
{
printf("! Failed to set WPD_OBJECT_NAME, hr = 0x%lx\n", hr);
}
}
// Add this property set to the collection
if (hr == S_OK)
{
hr = pPropertiesToWrite->Add(pValues);
if (FAILED(hr))
{
printf("! Failed to add values to collection, hr = 0x%lx\n", hr);
}
}
PropVariantClear(&pv);
}
}
示例创建包含对象标识符和名称对的 IPortableDeviceValuesCollection 对象后，可以开始异步操作。
当示例调用 IPortableDevicePropertiesBulk：：QueueSetValuesByObjectList 方法时，异步写入操作开始。 此方法通知驱动程序批量操作即将开始。 在此之后，示例调用 IPortableDeviceBulk：：Start 方法，开始实际编写新名称值。
HRESULT hr = S_OK;
GUID guidContext = GUID_NULL;
CSetBulkValuesCallback* pCallback = NULL;
CComPtr<IPortableDeviceProperties> pProperties;
CComPtr<IPortableDevicePropertiesBulk> pPropertiesBulk;
CComPtr<IPortableDeviceValues> pObjectProperties;
CComPtr<IPortableDeviceContent> pContent;
CComPtr<IPortableDeviceValuesCollection> pPropertiesToWrite;
CComPtr<IPortableDevicePropVariantCollection> pObjectIDs;
DWORD cObjectIDs = 0;
if (SUCCEEDED(hr))
{
hr = pPropertiesBulk->QueueSetValuesByObjectList(pPropertiesToWrite,
pCallback,
&guidContext);
if(SUCCEEDED(hr))
{
// Cleanup any previously created global event handles.
if (g_hBulkPropertyOperationEvent != NULL)
{
CloseHandle(g_hBulkPropertyOperationEvent);
g_hBulkPropertyOperationEvent = NULL;
}
// In order to create a simpler to follow example we create and wait infinitly
// for the bulk property operation to complete and ignore any errors.
// Production code should be written in a more robust manner.
// Create the global event handle to wait on for the bulk operation
// to complete.
g_hBulkPropertyOperationEvent = CreateEvent(NULL, FALSE, FALSE, NULL);
if (g_hBulkPropertyOperationEvent != NULL)
{
// Call Start() to actually being the Asynchronous bulk operation.
hr = pPropertiesBulk->Start(guidContext);
if(FAILED(hr))
{
printf("! Failed to start property operation, hr = 0x%lx\n", hr);
}
}
else
{
printf("! Failed to create the global event handle to wait on for the bulk operation. Aborting operation.\n");
}
}
else
{
printf("! QueueSetValuesByObjectList Failed, hr = 0x%lx\n", hr);
}
}
请注意，该示例等待操作完成的时间无限长。 如果这是生产应用程序，则需要修改代码。
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