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CHAIN_MSG_MAP

 

Defines an entry in a message map.

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CHAIN_MSG_MAP( theChainClass )

theChainClass

[in] The name of the base class containing the message map.

CHAIN_MSG_MAP directs messages to a base class's default message map (declared with BEGIN_MSG_MAP). To direct messages to a base class's alternate message map (declared with ALT_MSG_MAP), use CHAIN_MSG_MAP_ALT.

System_CAPS_noteNote

Always begin a message map with BEGIN_MSG_MAP. You can then declare subsequent alternate message maps with ALT_MSG_MAP. The END_MSG_MAP macro marks the end of the message map. Every message map must have exactly one instance of BEGIN_MSG_MAP and END_MSG_MAP.

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

Example

C++
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class CMyExtClass : public CMyBaseClass
{
public:
  BEGIN_MSG_MAP(CMyExtClass)
     MESSAGE_HANDLER(WM_PAINT, OnPaint)
     // chain to default message map in CMyBaseClass
     CHAIN_MSG_MAP(CMyBaseClass)
  ALT_MSG_MAP(1)
     // chain to first alternative message map in CMyBaseClass
     CHAIN_MSG_MAP(CMyBaseClass)
  ALT_MSG_MAP(2)
     MESSAGE_HANDLER(WM_CHAR, OnChar)
     // chain to alternate message map in CMyBaseClass
     CHAIN_MSG_MAP_ALT(CMyBaseClass, 1)
  END_MSG_MAP()

   LRESULT OnPaint(UINT /*nMsg*/, WPARAM /*wParam*/, LPARAM /*lParam*/, 
      BOOL& /*bHandled*/)
   {
      return 0;   
   }

   LRESULT OnChar(UINT /*nMsg*/, WPARAM /*wParam*/, LPARAM /*lParam*/, 
      BOOL& /*bHandled*/)
   {
      return 0;   
   }
};

This example illustrates the following:

  • If a window procedure is using CMyClass's default message map and OnPaint does not handle a message, the message is directed to CMyBaseClass's default message map for processing.

  • If a window procedure is using the first alternate message map in CMyClass, all messages are directed to CMyBaseClass's default message map.

  • If a window procedure is using CMyClass's second alternate message map and OnChar does not handle a message, the message is directed to the specified alternate message map in CMyBaseClass. CMyBaseClass must have declared this message map with ALT_MSG_MAP(1).

Requirements

Header: atlwin.h

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