ptr::GetInterface

Returns a pointer to the owned COM object.

_interface_type * GetInterface();

Возвращаемое значение

A pointer to the owned COM object.

Исключения

Internally, QueryInterface is called on the owned COM object and any error HRESULT is converted to an exception by ThrowExceptionForHR.

Заметки

The com::ptr adds a reference to the COM object on the caller's behalf and also keeps its own reference on the COM object. The caller must ultimately release the reference on the returned object or it will never be destroyed.

Пример

This example implements a CLR class that uses a com::ptr to wrap its private member IXMLDOMDocument object. The GetDocument member function uses GetInterface to return a pointer to the COM object.

// comptr_getinterface.cpp
// compile with: /clr /link msxml2.lib
#include <msxml2.h>
#include <msclr\com\ptr.h>

#import <msxml3.dll> raw_interfaces_only

using namespace System;
using namespace System::Runtime::InteropServices;
using namespace msclr;

// a ref class that uses a com::ptr to contain an 
// IXMLDOMDocument object
ref class XmlDocument {
public:
   // construct the internal com::ptr with a null interface
   // and use CreateInstance to fill it
   XmlDocument(String^ progid) {
      m_ptrDoc.CreateInstance(progid);   
   }

   // add a reference to and return the COM object
   // but keep an internal reference to the object
   IXMLDOMDocument* GetDocument() {
      return m_ptrDoc.GetInterface();
   }

   // simplified function that only writes the first node
   void WriteDocument() {
      IXMLDOMNode* pNode = NULL;
      BSTR bstr = NULL;

      try {
         // use operator -> to call XML Doc member
         Marshal::ThrowExceptionForHR(m_ptrDoc->get_firstChild(&pNode));
         if (NULL != pNode) {
            // write out the xml
            Marshal::ThrowExceptionForHR(pNode->get_nodeName(&bstr));
            String^ strName = gcnew String(bstr);
            Console::Write("<{0}>", strName);
            ::SysFreeString(bstr);
            bstr = NULL;

            Marshal::ThrowExceptionForHR(pNode->get_text(&bstr));
            Console::Write(gcnew String(bstr));
            ::SysFreeString(bstr);
            bstr = NULL;

            Console::WriteLine("</{0}>", strName);
         }
      }
      finally {
         if (NULL != pNode) {
            pNode->Release();
         }
         ::SysFreeString(bstr);
      }
   }

   // note that the destructor will call the com::ptr destructor
   // and automatically release the reference to the COM object

private:
   com::ptr<IXMLDOMDocument> m_ptrDoc;
};

// unmanaged function that loads XML into a raw XML DOM Document object
HRESULT LoadXml(IXMLDOMDocument* pDoc, BSTR bstrXml) {
   HRESULT hr = S_OK;
   VARIANT_BOOL bSuccess;
   hr = pDoc->loadXML(bstrXml, &bSuccess);
   if (S_OK == hr && !bSuccess) {
      hr = E_FAIL;
   }
   return hr;
}


// use the ref class to handle an XML DOM Document object
int main() {
   IXMLDOMDocument* pDoc = NULL;
   BSTR bstrXml = NULL;

   try {
      // create the class from a progid string
      XmlDocument doc("Msxml2.DOMDocument.3.0");

      bstrXml = ::SysAllocString(L"<word>persnickety</word>");
      if (NULL == bstrXml) {
         throw gcnew OutOfMemoryException("bstrXml");
      }
      // detach the document object from the ref class
      pDoc = doc.GetDocument();
      // use unmanaged function and raw object to load xml
      Marshal::ThrowExceptionForHR(LoadXml(pDoc, bstrXml));
      // release reference to document object (but ref class still references it)
      pDoc->Release();
      pDoc = NULL;

      // call another function on the ref class
      doc.WriteDocument();
   }
   catch (Exception^ e) {
      Console::WriteLine(e);   
   }
   finally {
      if (NULL != pDoc) {
         pDoc->Release();
      }
      
   }
}

<word>persnickety</word>

Требования

Header file <msclr\com\ptr.h>

Namespace msclr::com

См. также

Основные понятия

ptr Members

ptr::QueryInterface