Professional OPC
Development Tools

logos

Online Forums

Technical support is provided through Support Forums below. Anybody can view them; you need to Register/Login to our site (see links in upper right corner) in order to Post questions. You do not have to be a licensed user of our product.

Please read Rules for forum posts before reporting your issue or asking a question. OPC Labs team is actively monitoring the forums, and replies as soon as possible. Various technical information can also be found in our Knowledge Base. For your convenience, we have also assembled a Frequently Asked Questions page.

Do not use the Contact page for technical issues.

DUE TO ADMINISTRATIVE REASONS, WE MAY NOT BE ABLE TO RESPOND (OR TO RESPOND AS QUICKLY AS USUAL) BETWEEN August 19 - August 30, 2022. WE APOLOGIZE FOR INCONVENIENCE.

Example - OPC SubscribeMultipleItems in VC++

More
26 May 2014 08:46 #1996 by support
Hello,

here is an example of subscribing to OPC item changes in C++, using the ItemChanged event on the EasyDAClient object:
 
// This example shows how to subscribe to changes of multiple items and display the value of the item with each change.
// SubscribeMultipleItems.cpp : Defines the entry point for the console application.
//
 
#include "stdafx.h"
#include <atlcom.h>
#include <atlsafe.h>
#include <comutil.h>
 
#import "libid:FAB7A1E3-3B79-4292-9C3A-DF39A6F65EC1" version(5.2)	// EasyOpcLib
using namespace EasyOpcLib;
 
#define DISPID_EASYDACLIENTEVENTS_ITEMCHANGED 1002
 
//
 
class CSubscribeMultipleItemsModule : public ATL::CAtlModuleT< CSubscribeMultipleItemsModule >
{
};
 
CSubscribeMultipleItemsModule _AtlModule;
 
// CCoEasyDAClientEvents
 
class CCoEasyDAClientEvents : 
    public CComObjectRoot,
    public IDispEventImpl<1, CCoEasyDAClientEvents, &__uuidof(DEasyDAClientEvents), &__uuidof(__EasyOpcLib), 5, 2>
{
 
BEGIN_COM_MAP(CCoEasyDAClientEvents)
    COM_INTERFACE_ENTRY_IID(__uuidof(IDispatch), CCoEasyDAClientEvents)
    COM_INTERFACE_ENTRY_IID(__uuidof(DEasyDAClientEvents), CCoEasyDAClientEvents)
END_COM_MAP()
 
BEGIN_SINK_MAP(CCoEasyDAClientEvents)
    // Event handlers must have the __stdcall calling convention
    SINK_ENTRY_EX(1, __uuidof(DEasyDAClientEvents), DISPID_EASYDACLIENTEVENTS_ITEMCHANGED, 
        &CCoEasyDAClientEvents::ItemChanged)
END_SINK_MAP()
 
public:
    // The handler for EasyDAClient.ItemChanged event
    STDMETHOD(ItemChanged)(VARIANT varSender, VARIANT varEventArgs)
    {
        // Obtain the event arguments
        IEasyDAItemChangedEventArgsPtr EasyDAItemChangedEventArgsPtr(varEventArgs);
 
        IDAItemDescriptorPtr DAItemDescriptorPtr(EasyDAItemChangedEventArgsPtr->ItemDescriptor);
        IDAVtqPtr VtqPtr(EasyDAItemChangedEventArgsPtr->Vtq);
 
        // Not shown in this example: You should test the VtqPtr against NULL.
        _tprintf(_T("%s: %s\n"), COLE2CT(_bstr_t(DAItemDescriptorPtr->ItemId)), COLE2CT(_bstr_t(VtqPtr->ToString())));
 
        return S_OK;
    }
};
 
//
 
int _tmain(int argc, _TCHAR* argv[])
{
    // Initialize the COM library
    CoInitializeEx(NULL, COINIT_MULTITHREADED);
 
    // Instatiate the EasyOPC-DA client object
    IEasyDAClientPtr EasyDAClientPtr(__uuidof(EasyDAClient));
 
    // Hook the event handler
    IConnectionPointContainerPtr ConnectionPointContainerPtr(EasyDAClientPtr);
    IConnectionPointPtr ConnectionPointPtr;
    ConnectionPointContainerPtr->FindConnectionPoint(__uuidof(DEasyDAClientEvents), &ConnectionPointPtr);
 
    CComObject<CCoEasyDAClientEvents>* pCoEasyDAClientEvents = NULL;
    CComObject<CCoEasyDAClientEvents>::CreateInstance(&pCoEasyDAClientEvents);
    DEasyDAClientEventsPtr EasyDAClientEventsPtr(pCoEasyDAClientEvents);
 
    DWORD Cookie;
    ConnectionPointPtr->Advise(EasyDAClientEventsPtr, &Cookie);
 
    // Create array of OPC item IDs
    CComSafeArray<BSTR> ItemIdArray(4);
    ItemIdArray[0] = _T("Simulation.Random");
    ItemIdArray[1] = _T("Trends.Ramp (1 min)");
    ItemIdArray[2] = _T("Trends.Sine (1 min)");
    ItemIdArray[3] = _T("Simulation.Register_I4");
 
    CComVariant vResults(EasyDAClientPtr->SubscribeMultipleItems(
        /*varMachineNames:*/            _T(""), 
        /*varServerClasses:*/           _T("OPCLabs.KitServer.2"), 
        /*varItemIds:*/                 CComVariant(ItemIdArray.Detach()), 
        /*varRequestedUpdateRates:*/    1000));
 
    CComSafeArray<VARIANT> ResultArray(vResults.parray);
    for (int i = ResultArray.GetLowerBound(0); i <= ResultArray.GetUpperBound(0); i++)
    {
        IHandleResultPtr HandleResultPtr(ResultArray[i]);
        // Not shown in this example: Obtain the handle of the subscribed item from HandleResultPtr.
        // The handle is needed if you later wish to unsubscribe from certain items individually.
    }
 
    _tprintf(_T("Processing item changed events for 1 minute..."));
    Sleep(60*1000);
 
    // Unsubscribe from changes to all OPC items
    EasyDAClientPtr->UnsubscribeAllItems();
 
    // Release all interface pointers BEFORE calling CoUninitialize()
    ResultArray.Destroy();
    vResults.Clear();
    EasyDAClientEventsPtr = NULL;
    ConnectionPointPtr = NULL;
    ConnectionPointContainerPtr = NULL;
    EasyDAClientPtr = NULL;
 
    CoUninitialize();
    return 0;
}
 

The project file is attached as well.

File Attachment:

File Name: SubscribeM...5-26.zip
File Size:7 KB
Attachments:

Please Log in or Create an account to join the conversation.

Moderators: support
Time to create page: 0.063 seconds