mfc - sendmessage/postmessage with custom parameters

Question

I want to have a message handler in MFC which accepts whatever parameters I define in the message-map.

For example,

static UINT UWM_STATUS_MSG = RegisterWindowMessage("Status message");
static UINT UWM_GOT_RESULT= RegisterWindowMessage("Result has been obtained");

//{{AFX_MSG(MyClass)
    afx_msg void OnCustomStringMessage(LPCTSTR);
    afx_msg void OnStatusMessage();
//}}AFX_MSG


BEGIN_MESSAGE_MAP(MyClass, CDialog)
    //{{AFX_MSG_MAP(MyClass)
        ON_REGISTERED_MESSAGE(UWM_STATUS_MSG, OnStatusMessage)
        ON_REGISTERED_MESSAGE(UWM_GOT_RESULT, OnCustomStringMessage)
    //}}AFX_MSG_MAP
END_MESSAGE_MAP()

void MyClass::OnCustomStringMessage(LPCTSTR result)
{
    m_result.SetWindowText(result);
}

void MyClass::OnStatusMessage()
{
    // Do something
}

DWORD WINAPI MyClass::thread(LPVOID lParam)
{
    char result[256] = { 0 };
    SendMessage(UWM_STATUS_MSG);

    // Do some stuff and store the result

    PostMessage(UWM_GOT_RESULT, result);
}

Is such a thing possible?

Jabberwocky Jabberwocky · Accepted Answer · 2013-03-25T10:03:45

The signature of member functions that are invoked via ON_MESSAGE or ON_REGISTERED_MESSAGE must be:

afx_msg LRESULT OnMyFunction(WPARAM p1, LPARAM p2);

You have to deal with that using cast operators.

Therefore you should write this:

...
afx_msg LRESULT OnCustomStringMessage(WPARAM p1, LPARAM p2);
...

LRESULT MyClass::OnCustomStringMessage(WPARAM p1, LPARAM p2)
{
  LPCTSTR result = (LPCTSTR)p1 ;
   m_result.SetWindowText(result);
}

DWORD WINAPI MyClass::thread(LPVOID lParam)
{
    static char result[256] = { 0 };   // we need a static here
                                       // (see explanations from previous answers)
    SendMessage(UWM_STATUS_MSG);

    // Do some stuff and store the result

    PostMessage(UWM_GOT_RESULT, (WPARAM)result);
}

If MyClass::thread is meant to be invoked from several different threads you need to deal with the result array in a more compilcated manner that just declaring it static, for example allocating the array in MyClass::thread ands deleting it in OnCustomStringMessage as suggested by user2173190's answer.

mfc - sendmessage/postmessage with custom parameters

3 Answers