iWMDMStorage3：：GetMetadata 方法 (mswmdm.h)

發行項
02/29/2024

GetMetadata 方法會擷取與記憶體相關聯的元數據。

語法

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

參數

[out] ppMetadata

與記憶體相關聯的 IWMDMMetaData 指標指標指標指標。呼叫端負責在此介面上呼叫 Release ，並在完成時呼叫所有已配置的值，如探索裝置格式功能中的「清除已配置的記憶體」所述。

傳回值

方法會傳回 HRESULT。 Windows Media 中的所有介面方法裝置管理員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

這個方法會擷取與記憶體相關聯的所有元數據。如果應用程式正在搜尋特定的元數據，呼叫 IWMDMStorage4：：GetSpecifiedMetadata 可能會更有效率。

從 Windows 可攜式裝置 (WPD) 裝置擷取數據時，數據會以二進位格式傳回。應用程式應該取消串行化此數據，以取得實際的屬性值。

範例

下列 C++ 函式會擷取與記憶體相關聯的所有元數據。


// Function to print out all the metadata associated with a storage.
HRESULT CWMDMController::GetMetadata(IWMDMStorage *pStorage)
{
   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
   {
      CComPtr<IWMDMStorage3> pStorage3;
      CComPtr<IWMDMMetaData> pMetadata;
      hr = pStorage->QueryInterface(__uuidof(IWMDMStorage3), (void**)&pStorage3);
      BREAK_HR(hr, "Got an IWMDMStorage3 interface in GetMetadata.", "Couldn't get an IWMDMStorage3 interface in GetMetadata.");

      hr = pStorage3->GetMetadata(&pMetadata);
      BREAK_HR(hr, "Got an IWMDMMetaData interface in GetMetadata.", "Couldn't get an IWMDMMetaData interface in GetMetadata.");

      //
      // Loop through all metadata properties, and print out the value of each.
      //
      BYTE* value;
      WMDM_TAG_DATATYPE type;
      UINT len = 0;
      UINT count = 0;
      WCHAR* name;
      // Get the number of metadata items.
      hr = pMetadata->GetItemCount(&count);

      BREAK_HR(hr, "Got a metadata count in GetMetadata.", "Couldn't get a metadata count in GetMetadata.");
      for(;count > 0; count--)
      {
         // Get the metadata property by index.
         WCHAR* name;
         hr = pMetadata->QueryByIndex(count-1, &name, &type, &value, &len);
         if (SUCCEEDED(hr))
         {
            // TODO: Display the property name.
            CoTaskMemFree(name);

            // Print out the value of the property, according to the value type.
            switch (type)
            {
            case WMDM_TYPE_QWORD:
            case WMDM_TYPE_DWORD:
            case WMDM_TYPE_WORD:
               // TODO: Display the value.
               break;
            case WMDM_TYPE_STRING:
               // TODO: Display the value.
               // Release the method-allocated property value memory.
                    if (SUCCEEDED(hr))
                        CoTaskMemFree(value);
               break;
            case WMDM_TYPE_BOOL:
               // TODO: Display the value.
               break;
            case WMDM_TYPE_BINARY:
               // TODO: Display the value.
               break;
            case WMDM_TYPE_DATE:
               {
                  WMDMDATETIME *val = (WMDMDATETIME*)value;
                        // TODO: Display the month, day, and year.
               }
               break;
            case WMDM_TYPE_GUID:
               {
                  WCHAR strGuid[64];
                  StringFromGUID2(reinterpret_cast<GUID&>(value),(LPOLESTR)strGuid, 64);
                  // TODO: Display the GUID value.
               }
               break;
            default:
               // TODO: Display the message: "Could not understand the returned value type
            }
         }
         else // Couldn't get the metadata property at index count - 1.
            // TODO: Display the message: 
            // "Couldn't get a value for index " 
            // followed by the current index value.
      }

      // Now get a specific property by name.
      // If this property isn't supported, the method returns E_INVALIDARG.
      hr = pMetadata->QueryByName(g_wszWMDMFileName, &type, &value, &len);
      if (hr == S_OK) 
      {
         wstring wstr((wchar_t*)value, len / 2); // Create a string from the name.
            // TODO: Display the file name.
            CoTaskMemFree(value);
      }

      // See if file is DRM-protected.
      hr = pMetadata->QueryByName(g_wszWMDMIsProtected, &type, &value, &len);
      if (hr == S_OK)
      {
         // TODO: Display a message that the object is DRM protected.
      }


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

   // Clean up and return.
   return hr;
}