Adding an Event Handler for the Button （OutLook）

Adding an Event Handler for the Button created in previous tutorial

In the previous tutorials, we have seen how to add a toolbar and thus create a button in Microsoft Outlook. Now, in this tutorial, we will see how to invoke an event handler for the button, or in terms of COM, how to advise the Button event!.

The idea behind this tutorial is simple, we need to display a message box saying, "Button Clicked", when we click on the button created. For this, we have to capture the Button Click Event, i.e., CommandBar Events. The disp interface responsible for this is _CommandBarButtonEvents. So now, if we implement this sink interface that will be called by the event source, then our job is over.

IDispEventSimpleImpl<>

So, here we have to create a connection point between our button and interface in simple words. The IDispEventSimpleImpl<> interface provides the connection points for an ATL COM Object. It is also used to implement an event dispinterface. Now, we have to derive our class from this interface. This is done as follows:

class ATL_NO_VTABLE CAddin : 
    public CComObjectRootEx<CComSingleThreadModel>,
    public CComCoClass<CAddin, &CLSID_Addin>,
    public IDispatchImpl<IAddin, &IID_IAddin, &LIBID_OUTLOOKADDINLib>,
    public IDispatchImpl<_IDTExtensibility2, 
        &IID__IDTExtensibility2, &LIBID_AddInDesignerObjects>,
    //the derivation is done here
    public IDispEventSimpleImpl<1,CAddin, 
        &__uuidof(Office::_CommandBarButtonEvents)> 
Parameters:

1. The first parameter is a unique identifier for the source object.
2. The second parameter is the user's class, so here we have CAddin.
3. The third parameter is pointer to IID of the event dispinterface by this class.
4. Here our dispinterface is Office::_CommandBarButtonEvents. For help, please refer Microsoft Outlook Object Model.

A Simple Shortcut:

Now, we do a simple shortcut to make our job easier. We add this code before the constructor in our file:

public:
//the added code is here
 typedef IDispEventSimpleImpl</*nID =*/ 1, 
    CAddin, &__uuidof(Office::_CommandBarButtonEvents)> CommandButton1Events;
 CAddin()
 {
 }

As we can see, this can help in advising our sink since we are doing typedef here. If you get confused here, please do feel free to proceed to the next step.

Sink Entry:

In order to move with sinks, we have to have entries for our event notifications to be handled by their proper functions as we have for Messages in MFC and Win32.

So, we need to enter the SINK ENTRY as follows after END_COM_MAP() macro.

BEGIN_SINK_MAP(CAddin)
SINK_ENTRY_INFO(1, __uuidof(Office::_CommandBarButtonEvents),0x01, 
                               OnClickButton, &OnClickButtonInfo)
END_SINK_MAP() 
in SINK_ENTRY_INFO

We have specified our unique identifier, IID identifying the dispatch interface, dispid identifying the specified event, name of the event handler function, and the last parameter corresponds to type information. This is provided in the form of ATL_FUNC_INFO structure. We do it in Addin.cpp file.

_ATL_FUNC_INFO OnClickButtonInfo = 
  {CC_STDCALL,VT_EMPTY,2,{VT_DISPATCH,VT_BYREF | VT_BOOL}}; 

Setting up our CallBack:

1. We define our callback as follows:

   void __stdcall 
         OnClickButton(IDispatch * /*Office::_CommandBarButton**/ Ctrl, 
         VARIANT_BOOL * CancelDefault); 

2. Next would be our declaration of our OnClickButton function which is added at the top of Addin.h.

   extern _ATL_FUNC_INFO OnClickButtonInfo;

3. The next and final step is to write our function! So, here is the function, in Addin.cpp.

   void __stdcall CAddin::OnClickButton(IDispatch* Ctrl, 
                                   VARIANT_BOOL * CancelDefault)
   {
       MessageBox(NULL, "U Have Clicked Me, 
                               Friend", "OnClickButton", MB_OK);
   }

That's it....we have completed our second tutorial of getting a message box when we press the button...hmm...it looks so simple and sure it is.