ptr::operator=

Статья
10/16/2008

Attaches a COM object to a com::ptr.

ptr<_interface_type> % operator=(
   _interface_type * _right
);

Параметры

_right
The COM interface pointer to attach.

Возвращаемое значение

A tracking reference on the com::ptr.

Исключения

If the com::ptr already owns a reference to a COM object, operator= throws InvalidOperationException.

Заметки

Assigning a COM object to a com::ptr references the COM object but does not release the caller's reference to it.

This operator has the same effect as Attach.

Пример

This example implements a CLR class that uses a com::ptr to wrap its private member IXMLDOMDocument object. The ReplaceDocument member function first calls Release on any previously owned object and then uses operator= to attach a new document object.

// comptr_op_assign.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);   
   }

   // replace currently held COM object with another one
   void ReplaceDocument(IXMLDOMDocument* pDoc) {
      // release current document object
      m_ptrDoc.Release();
      // attach the new document object
      m_ptrDoc = pDoc;
   }

   // 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 creates a raw XML DOM Document object
IXMLDOMDocument* CreateDocument() {
   IXMLDOMDocument* pDoc = NULL;
   Marshal::ThrowExceptionForHR(CoCreateInstance(CLSID_DOMDocument30, NULL,
      CLSCTX_INPROC_SERVER, IID_IXMLDOMDocument, (void**)&pDoc));
   return pDoc;
}


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

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

      // get another document object from unmanaged function and
      // store it in place of the one held by the ref class
      pDoc = CreateDocument();
      doc.ReplaceDocument(pDoc);
      // no further need for raw object reference
      pDoc->Release();
      pDoc = NULL;
   }
   catch (Exception^ e) {
      Console::WriteLine(e);   
   }
   finally {
      if (NULL != pDoc) {
         pDoc->Release();
      }
   }
}