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ALT_MSG_MAP

Marks the beginning of an alternate message map.

ALT_MSG_MAP( msgMapID )

msgMapID

[in] The message map identifier.

ATL identifies each message map by a number. The default message map (declared with the BEGIN_MSG_MAP macro) is identified by 0. An alternate message map is identified by msgMapID.

Message maps are used to process messages sent to a window. For example, CContainedWindow allows you to specify the identifier of a message map in the containing object. CContainedWindow::WindowProc then uses this message map to direct the contained window's messages either to the appropriate handler function or to another message map. For a list of macros that declare handler functions, see BEGIN_MSG_MAP.

Always begin a message map with BEGIN_MSG_MAP. You can then declare subsequent alternate message maps.

The END_MSG_MAP macro marks the end of the message map. Note that there is always exactly one instance of BEGIN_MSG_MAP and END_MSG_MAP.

For more information about using message maps in ATL, see Message Maps.

The following example shows the default message map and one alternate message map, each containing one handler function:

BEGIN_MSG_MAP(CMyOneAltClass)
   MESSAGE_HANDLER(WM_PAINT, OnPaint)
ALT_MSG_MAP(1)
   MESSAGE_HANDLER(WM_SETFOCUS, OnSetFocus)
END_MSG_MAP()

The next example shows two alternate message maps. The default message map is empty.

BEGIN_MSG_MAP(CMyClass)
ALT_MSG_MAP(1)
   MESSAGE_HANDLER(WM_PAINT, OnPaint)
   MESSAGE_HANDLER(WM_SETFOCUS, OnSetFocus)
ALT_MSG_MAP(2)
   MESSAGE_HANDLER(WM_CREATE, OnCreate)
END_MSG_MAP()

Header: atlwin.h

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