IWMDMStorage3：：CreateEmptyMetadataObject 方法 (mswmdm.h)

發行項
03/05/2024

CreateEmptyMetadataObject 方法會建立新的 IWMDMMetaData 介面。這個介面是用來設定或擷取記憶體的元數據屬性。

語法

HRESULT CreateEmptyMetadataObject(
  [out] IWMDMMetaData **ppMetadata
);

參數

[out] ppMetadata

接收新的 IWMDMMetaData 介面。呼叫端必須在完成時釋放這個介面。

傳回值

方法會傳回 HRESULT。 Windows Media 中的所有介面方法裝置管理員都可以傳回下列任何錯誤碼類別：

標準 COM 錯誤碼
轉換成 HRESULT 值的 Windows 錯誤碼
Windows Media 裝置管理員錯誤碼

如需可能錯誤碼的廣泛清單，請參閱錯誤碼。

備註

建立的元數據介面不會隱含地連接到建立它的記憶體;它只是空的元數據容器。您必須將介面提交至方法來設定或擷取元數據值。

範例

下列 C++ 函式會將檔案傳送至裝置。在傳輸過程中，它必須將元數據新增至記憶體，以指定新的記憶體類型。


HRESULT mySendFile(LPCWSTR pwszFileName, IWMDMStorage* pStorage, IWMDMOperation* pOperation)
{
   HRESULT hr = S_OK;

   // A dummy loop to handle unrecoverable errors. When we hit an error we
   // can't handle or don't like, we just use a 'break' statement.
   // The custom BREAK_HR macro checks for failed HRESULT values and does this.
   do
   {
      if (pwszFileName == NULL || pStorage == NULL)
      {
         BREAK_HR(E_POINTER,"","Bad pointer passed in.");
         return E_POINTER;
      }

      // Make sure the destination is a folder.
      DWORD attributes = 0;
      _WAVEFORMATEX format;
      hr = pStorage->GetAttributes(&attributes, &format);
      if (!(attributes | WMDM_FILE_ATTR_FOLDER))
      {
         BREAK_HR(E_FAIL, "", "Storage submitted to mySendFile is not a folder.");
         return E_FAIL;
      }

      // Transcode the file
      hr = myTranscodeMethod(pwszFileName);
      BREAK_HR(hr, "Couldn't transcode the file in mySendFile.", "Transcoded the file in mySendFile.");
      //
      // Let's set some metadata in the storage.
      //
      CComPtr<IWMDMStorage3> pStorage3;
      hr = pStorage->QueryInterface(__uuidof(IWMDMStorage3), (void**)(&pStorage3));
      BREAK_HR(hr, "Got an IWMDMStorage3 interface in mySendFile.","Couldn't get an IWMDMStorage3 in mySendFile.");

      // First create the IWMDMMetaData interface.
      IWMDMMetaData* pMetadata;
      hr = pStorage3->CreateEmptyMetadataObject(&pMetadata);
      BREAK_HR(hr,"Created an IWMDMMetaData interface in mySendFile.","Couldn't create an IWMDMMetaData interface in mySendFile.");

      //
      // Set the file format.
      //
      WMDM_FORMATCODE fileFormat = myGetWMDM_FORMATCODE(pwszFileName);
      hr = pMetadata->AddItem(WMDM_TYPE_DWORD, g_wszWMDMFormatCode, (BYTE*)&fileFormat, sizeof(WMDM_TYPE_DWORD));


      //
      // Get the proper interface and transfer the file.
      //
      CComPtr<IWMDMStorageControl3> pStgCtl3;
      CComPtr<IWMDMStorage> pNewStorage;
      hr = pStorage->QueryInterface(__uuidof(IWMDMStorageControl3),(void**)(&pStgCtl3));

      // Get the simple file name to use for the destination file.
      wstring destFile = pwszFileName;
      destFile = destFile.substr(destFile.find_last_of(L"\\") + 1);

      // Get a progress indicator.
      CComQIPtr<IWMDMProgress> pProgress(this);

      // Set the flags for the operation
      UINT flags = WMDM_MODE_BLOCK | // Synchronous call. 
         WMDM_STORAGECONTROL_INSERTINTO | // Insert it into the destination folder.
         WMDM_CONTENT_FILE | // We're inserting a file.
         WMDM_FILE_CREATE_OVERWRITE; // Overwrite existing files.
      if (pOperation != NULL)
         flags |= WMDM_CONTENT_OPERATIONINTERFACE;

      // Send the file and metadata.
      hr = pStgCtl3->Insert3(
         flags,
         WMDM_FILE_ATTR_FOLDER, // The current storage is a folder.
         const_cast<WCHAR*>(pwszFileName), // Source file.
         NULL, // Destination file name.
         pOperation, // Null to allow WMDM to read the file; non-null to present raw data bytes to WMDM.
         pProgress, // Interface to send simple progress notifications.
         pMetadata, // IWMDMMetaData interface previously created and filled.
         NULL, 
         &pNewStorage);
      if (FAILED(hr))
         m_pLogger->LogDword(WMDM_LOG_SEV_ERROR, NULL, "Error calling Insert3 in mySendFile: %lX", hr);
      BREAK_HR(hr, "Wrote a file to the device in mySendFile", "Couldn't write to the device in mySendFile.");

   } while (FALSE); // End of dummy loop

   return hr;
}