Knowledge Base

AtlEvnt.exe sample shows how to creates ATL sinks by using the ATL IDispEventImpl and IDispEventSimpleImpl classes

Article ID: 194179

Article Last Modified on 6/2/2005

APPLIES TO

Microsoft ActiveX Template Library 3.0, when used with:
- Microsoft Visual C++ 6.0 Enterprise Edition
- Microsoft Visual C++ 6.0 Professional Edition
- Microsoft Visual C++ 6.0 Standard Edition
- Microsoft Visual C++ .NET 2002 Standard Edition
- Microsoft Visual C++ .NET 2003 Standard Edition

This article was previously published under Q194179

Microsoft Visual C++ .NET (2002) and Microsoft Visual C++ .NET (2003) support both the managed code model that is provided by the .NET Framework and the unmanaged native Windows code model. The information in this article applies to unmanaged Visual C++ code only.

SUMMARY

AtlEvnt.exe shows you how to implement an event sink using the ATL IDispEventImpl and IDispEventSimpleImpl classes. For composite controls or ATL dialogs, the wizard inserts IDispEventImpl in the inheritance list to set up the sink. So the focus of this sample is to create sinks for other types of COM objects and clients. This is only applicable to source interfaces of type dispinterface.

Use IDispEventImpl when you have access to a type library. Use IDispEventSimpleImpl when you do not have access to the type library or when you want to be more efficient by not loading the type library.

In addition to a link to the sample, the MORE INFORMATION section of this article includes an overview of the project and information on how to implement each class.

MORE INFORMATION

The following files are available for download from the Microsoft Download Center:

Visual C++ 6.0

Download Atlevnt.exe now

For more information about how to download Microsoft Support files, click the following article number to view the article in the Microsoft Knowledge Base:

119591 How to obtain Microsoft support files from online services

Microsoft scanned this file for viruses. Microsoft used the most current virus-detection software that was available on the date that the file was posted. The file is stored on security-enhanced servers that help prevent any unauthorized changes to the file.

Visual C++ .NET

Download Atlevntvcnet.exe now

Release Date: June 25, 2002

For more information about how to download Microsoft Support files, click the following article number to view the article in the Microsoft Knowledge Base:

119591 How to obtain Microsoft support files from online services

Microsoft scanned this file for viruses. Microsoft used the most current virus-detection software that was available on the date that the file was posted. The file is stored on security-enhanced servers that help prevent any unauthorized changes to the file. The ATLEVNT workspace consists of two projects, AtlEvnt and EventSrc. Use the -d option when you run AtlEvnt.exe:

AtlEvnt.exe -d

Project Overview

The AtlEvnt Workspace consists of two projects, AtlEvnt and EventSrc.

The EventSrc project is a default ATL DLL project with one "Simple Object." The simple object has no methods and has been modified to support connection points and the IPersist interface. The COM object exposes a default source interface (below) which has a single method called Tick. The COM object calls this method on all sink objects connected to it, based on a timer:

   dispinterface _EventSink
   {

      properties:
      methods:
      [id(1), helpstring("method Tick")] HRESULT Tick([in] long tckcnt);

   }

The AltEvnt project is an ATL EXE project. An ATL CDialogImpl class was added to turn the project into a simple dialog application. Four sinks were added to the project (two using IDispEventImpl and two using IDispEventSimpleImpl). Each sink illustrates a different way of providing a sink object to handle the Tick event fired by the EventSrc COM object.

The dialog box has four buttons and clicking a button enables connecting the corresponding sink to the EventSrc COM object. The list box displays a string of form "Sinkn : Tick Event Received - x" each time the Tick event handler in the sink is called. Once a connection is established, the button is disabled. If there is any problem establishing the connection then the button text is replaced with a string of form "Connect Err-hr" where "hr" represents the failure HRESULT. Use the "Error LookUp" tool that ships with Visual C++, version 6.0 to get an explanation of the error.

To run this sample, first build the EventSrc project and ensure the EventSrc object is successfully registered. Then build the AtlEvnt project and run it. A dialog box with four buttons (apart from OK and Cancel) and a list box is displayed. The four buttons represent four sinks. Clicking a button connects the sink to the source. Once the connection is made, strings are added to the list box each time a handler is called.

Steps to implement IDispEventImpl

Create a new class derived from IDispEventImpl. You can click New Class on the Insert menu to generate a new class. For each different sink, add an IDispEventImpl class to the inheritance list with a unique ID as the first parameter. The sink class can either be a COM object (as in a composite control) or a class that just derives from IdispEventImpl:

// Just a sink.
      class CSinkObj : public IDispEventImpl<IDC_OBJ, CSinkObj>
      {
         ...
      }

-or-

// COM object that also implements a sink (as in a composite
      // control).
      class ATL_NO_VTABLE CSinkObj :
         public CComObjectRootEx<CComSingleThreadModel>,
         public CComCoClass<CSinkObj, &CLSID_SinkObj>,
         public IDispatchImpl<ISinkObj, &IID_ISinkObj, &LIBID_SINKPROJLib>,
         public IDispEventImpl<IDC_SRCOBJ, CSinkObj>
      {
         ...
      }

You can either specify the source interface ID, the type library ID, major and minor version numbers of the type library containing the source interface explicitly as parameters of IdispEventImpl, or use the AtlGetObjectSourceInterface() to extract this information from the type library. Use of AtlGetObjectSourceInterface() requires that the COM object firing the event implement either IProvideClassInfo2 or IPersist*:

class CSinkObj : public IDispEventImpl<IDC_OBJ, CSinkObj>
      {
         ...
      }

-or-

class CSinkObj : public IDispEventImpl<IDC_OBJ, CSinkObj,
         &DIID__EventSink, // Source interface GUID.
         &LIBID_COMOBJLib, // typelib ID containing source interface.
         1,                // Major version # of LIBID_COMOBJLib.
         0>                // Minor version # of LIBID_COMOBJLib.
      {
         ...
      }

Add a sink map to the above class and a sink entry corresponding to each event of a source interface that you would like to handle. Use SINK_ENTRY_EX() when the source interface is specified as a parameter in IDispEventImpl, otherwise, use SINK_ENTRY():

class CSinkObj : public IDispEventImpl<IDC_SRCOBJ, CSinkObj>
      {
      public:
         BEGIN_SINK_MAP(CSinkObj)
            SINK_ENTRY(IDC_SRCOBJ, 1 /*DISPID*/, OnTick /*Event Handler*/)
         END_SINK_MAP()
         ...
      }

-or-

class CSinkObj : public IDispEventImpl<IDC_OBJ, CSinkObj,
                              &DIID__EventSink, &LIBID_COMOBJLib, 1, 0>
      {
      public:
         BEGIN_SINK_MAP(CSinkObj)
            SINK_ENTRY_EX(IDC_SRCOBJ, DIID__EventSink, 1, OnTick)
         END_SINK_MAP()
         ...
      }

Add event handler methods to your class. Make sure they have the __stdcall calling convention:

class CSinkObj : public IDispEventImpl<IDC_SRCOBJ, CSinkObj3>
      {
      public:
         BEGIN_SINK_MAP(CSinkObj)
            SINK_ENTRY(IDC_SRCOBJ, 1 , OnTick)
         END_SINK_MAP()


         // event handler for event defined in idl as
         // [id(1)] HRESULT Tick([in] long tckcnt);
         HRESULT __stdcall OnTick(long tickcnt)
         {
            ATLTRACE("CSinkObj::OnTick\n");
            return S_OK;
         }
         ...
      }

Connect the sink to the COM object by calling DispEventAdvise(). If the source interface is specified as a parameter to IDispEventImpl then call:

// pUnk is the IUnknown pointer of the COM object that fires events.
   // pSinkObj is an instance of the CSinkObj class.
      pSinkObj->DispEventAdvise(pUnk);

or else call:

// Make sure the COM object corresponding to pUnk implements
      // IProvideClassInfo2 or IPersist*.
      // Call this method to extract info about source type library if you
      // specified only two parameters to IdispEventImpl.
      AtlGetObjectSourceInterface(pUnk, &pSinkObj->m_libid,
         &pSinkObj->m_iid, &pSinkObj->m_wMajorVerNum,
         &pSinkObj->m_wMinorVerNum);

      hr = pSinkObj->DispEventAdvise(pUnk, &pSinkObj->m_iid);

Disconnect the sink by calling DispEventUnadvise():
```
pSinkObj->DispEventUnadvise(pUnk);
```

Steps to implement IDispEventSimpleImpl

Create a class derived from IDispEventSimpleImpl. The source interface has to be specified.
Follow step 3 above except add SINK_ENTRY_INFO() for each method of a source interface that you would like to handle. Since IDispEventSimpleImpl does not have access to the type library you have to provide information about each event handler through an _ATL_FUNC_INFO structure, one for each event handler.

Instead of specifying an _ATL_FUNC_INFO structure in SINK_ENTRY_INFO(), you can use the SINK_ENTRY_EX() macro and override the virtual function GetFuncInfoFromId() to fill in the _ATL_FUNC_INFO structure, as shown in the following code.

Follow steps 4 through 6 from above:

static _ATL_FUNC_INFO OnTickInfo = {
         CC_STDCALL,   // Calling convention.
         VT_I4,        // Return type.
         1,            // Number of arguments.
         {VT_I4}       // Argument types.
      };

      class CSinkObj :
         public IDispEventSimpleImpl<IDC_SRCOBJ, CSinkObj,
                &DIID__EventSink>
      {
      public:
      BEGIN_SINK_MAP(CSinkObj)
         SINK_ENTRY_INFO(IDC_SRCOBJ, DIID__EventSink, 1, OnTick,
                         &OnTickInfo)
      END_SINK_MAP()

         HRESULT __stdcall OnTick(long tickcnt)
         {
            ATLTRACE("CSinkObj::OnTick\n");
            return S_OK;
         }
         ...

      }

-or-

class CSinkObj :
         public IDispEventSimpleImpl<IDC_SRCOBJ, CSinkObj,
                &DIID__EventSink>
      {
      public:
      BEGIN_SINK_MAP(CSinkObj4)
         SINK_ENTRY_EX(IDC_SRCOBJ, DIID__EventSink, 1, OnTick)
         // Equivalent to:
         // SINK_ENTRY_INFO(IDC_SRCOBJ, DIID__EventSink, 1, OnTick, NULL)
      END_SINK_MAP()

         HRESULT GetFuncInfoFromId(const IID& iid, DISPID dispidMember,
            LCID lcid, _ATL_FUNC_INFO& info)
         {
            if (InlineIsEqualGUID(iid, DIID__EventSink))
            {
               info.cc = CC_STDCALL;
               switch(dispidMember)
               {
                  case 1:
                     info.vtReturn = VT_I4;
                     info.nParams = 1;
                     info.pVarTypes[0] =  VT_I4;
                     return S_OK;

                  default:
                     return E_FAIL;
               }
            }
            return E_FAIL;
         }

         HRESULT __stdcall OnTick(long tickcnt)
         {
            ATLTRACE("CSinkObj::OnTick\n");
            return S_OK;
         }
         ...
      }

REFERENCES

For more information, click the following article number to view the article in the Microsoft Knowledge Base:

181277 AtlSink uses ATL to create a dispinterface sink

Additional query words: listbox Atlevnt Atlevntvcnet

Keywords: kbhowto kbdownload kbtshoot kbfile kbsample kbconnpts kbfaq kbactivexevents KB194179

Microsoft KB Archive/194179

Contents

AtlEvnt.exe sample shows how to creates ATL sinks by using the ATL IDispEventImpl and IDispEventSimpleImpl classes

SUMMARY

MORE INFORMATION

Visual C++ 6.0

Visual C++ .NET

Project Overview

Steps to implement IDispEventImpl

Steps to implement IDispEventSimpleImpl

REFERENCES