ON_MESSAGE

Article
12/01/2015

Indicates which function will handle a user-defined message.

Syntax

ON_MESSAGE(
message
, 
memberFxn
)

Parameters

message
The message ID.
memberFxn
The name of the message-handler function to which the message is mapped.

The type of the function must be afx_msg LRESULT (CWnd::*)(WPARAM, LPARAM).

Remarks

User-defined messages are any messages that are not standard Windows WM_MESSAGE messages. When selecting a message ID, you must use values within the range of WM_USER (0x0400) to 0x7FFF or WM_APP (0x8000) to 0xBFFF. For more information regarding message IDs, see WM_APP.

There should be exactly one ON_MESSAGE macro statement in your message map for every user-defined message that must be mapped to a message-handler function.

Note

In addition to user-defined messages, ON_MESSAGE handles less common Windows messages. For more information, see Knowledge Base article 99848: INFO: Use ON_MESSAGE() Macro to Map Less-Common Messages.

For more information and examples, see Message Handling and Mapping Topics and User-Defined Handlers

Example

#define WM_MYMESSAGE (WM_USER + 100)

BEGIN_MESSAGE_MAP(CMyWnd2, CWnd)
   ON_MESSAGE(WM_MYMESSAGE, OnMyMessage)
END_MESSAGE_MAP()

// inside the class declaration
 afx_msg LRESULT OnMyMessage(WPARAM wParam, LPARAM lParam);

LRESULT CMyWnd2::OnMyMessage(WPARAM wParam, LPARAM lParam)
{
   UNREFERENCED_PARAMETER(wParam);
   UNREFERENCED_PARAMETER(lParam);

   // Handle message here.

   return 0;
}

Requirements

Header: afxmsg_.h