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Title |
Posting Messages
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Summary |
Posting Messages within an application is a simple method of communicating within various windows using message queues that don't tie up the system. |
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Contributor |
John McTainsh
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Published |
23-Sep-2000 |
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Last updated |
23-Sep-2000 |
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Description.
If the handle or pointer to the CWnd is available it is a simple task
to post a message to that window with numbers or a pointer to some memory. See the
article on "Getting pointers to Documents and Views" to see how to navigate
the application.
Setting up the Post/Send message.
A message must be defines higher than WM_USER. A good place
for this is in the StdAfx.h
#define UNUSED_MEMORY (0xcd) //Initialised memory
#define FREED_MEMORY (0xdd) //Deleted memory
#define ASSERT_USED(x) ASSERT( (BYTE)x[0] != UNUSED_MEMORY )
#define ASSERT_NOT_DELETED(x) ASSERT( (BYTE)x[0] != DELETED_MEMORY )
#define WM_MY_NUM_MESSAGE (WM_USER+23) //Number posting message
#define WM_MY_STRING_MESSAGE (WM_USER+24) //Memory posting message
Post or Send the the message to the other window as follows. Note Post
will return immediately and be processed when the the system is idle
to process messages. Send will be processed immediately. Any memory allocated
for the PostMessage should be freed when processed to ensure it is
not deleted before it is used. For safety it is best to do this for SendMessage
as well.
CWnd* pWndOther = AfxGetMainWnd(); //Get pointer to the window
ASSERT( pWndOhter );
//Post some numbers and Wait for return
pWndOther->SendMessage( WM_MY_NUM_MESSAGE, wSomeWord, lSomeLong );
//Post some Memory
LPCTSTR lpszName = new TCHAR[MY_STR_LEN+1];
if( lpszName != NULL )
{
strncpy( lpszName, _T("Some name data"), MY_STR_LEN );
lpszName[MY_STR_LEN-1] = NULL;
pWndOther->PostMessage( WM_MY_STRING_MESSAGE, wSomeWord, lpszName );
}
else
{
//TODO : Process no memory error
}
Processing the Message.
Notification of the message will be come through the message handler
the functions should be defined in the header/definition.
//}}AFX_MSG
afx_msg LONG OnNummber( WPARAM wSomeWord, LPARAM lSomeLong );
afx_msg LONG OnString( WPARAM wSomeWord, LPARAM lName );
DECLARE_MESSAGE_MAP()
In the implementation file add to the message map as follows.
//}}AFX_MSG_MAP
ON_MESSAGE(WM_MY_NUM_MESSAGE, OnNumber)
ON_MESSAGE(WM_MY_STRING_MESSAGE, OnString)
END_MESSAGE_MAP()
Now process the message.
// ***************************************************************************
//DESCRIPTION:
// Do something with the numbers
//PARAMS:
// wSomeWord Blah blah ....
// lSomeLong Blah blah ....
//RETURN:
// no relevant for PostMessage but used for SendMessage
//CREATED:
// 26-6-2000, 14:59:17 by john@mctainsh.com
// ***************************************************************************
LONG CMainFrame::OnNumber( WPARAM wSomeWord, LPARAM lSomeLong )
{
TRACE( _T("CMainFrame::OnNumber( %d, %ld )\n"), wSomeWord, lSomeLong );
return( wSomeWord + lSomeLong );
}
// ***************************************************************************
//DESCRIPTION:
// Do something with the string
//PARAMS:
// wSomeWord Blah blah ....
// lName Blah blah ....
//RETURN:
// no relevant for PostMessage but used for SendMessage
//CREATED:
// 26-6-2000, 14:59:17 by john@mctainsh.com
// ***************************************************************************
LONG CMainFrame::OnString( WPARAM wSomeWord, LPARAM lName )
{
TRACE( _T("CMainFrame::OnString( %d, %ld )\n"), wSomeWord, lName );
LPCTSTR lpszName = (LPCTSTR)lName; //Case MUST be appropiate
ASSERT( lpszName != NULL );
ASSERT_USED( lpszName );
ASSERT_NOT_DELETED( lpszName );
SetWindowTitle( lpszName );
delete [] lpszName;
//Return something useful only if the SendMessage is used
return( wSomeWord + 1 );
}
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