User message

[Oliver123]

My existing code is below. A global function which is not a member of any class is calling a function which is a member of class CNewDlg. This code works, but I don't like it. I'm using it because it's the best I have been able to do. I think it can be done better using a user message, but I don't know how user messages work and haven't been able to find any examples. How would I code this using a user message? void WINAPI HostChange(LinkPtr data) <---global; not in any class. A callback provides ptr data. { ((CNewDlg*)AfxGetApp()->m_pMainWnd)->LogonChange(data); } void CNewDlg::LogonChange(LinkPtr data) <---function in a dialog class { if(data->SomeField == 3){Do something...} }

[Ravi Bhavnani]

Oliver123 wrote:

This code works, but I don't like it.

I'm with you on this! :) Here's an ultra-easy alternative, which while not perfect, has its advantages.

1. Add 2 buttons (IDC_HOST_CHANGE and IDC_LOGON_CHANGE) to CNewDlg and make them invisible.

2. Write a handler for each - the one for IDC_HOST_CHANGE should call HostChange() and the one for IDC_LOGON_CHANGE should call LogonChange().

3. HostChange() and LogonChange() should get a pointer to an (perhaps the) instance of LinkPtr via a singleton access method exposed by your app class.

4. Your static callbacks should post the appropriate message to your app's AfxGetMainWnd(). No casting to CNewDlg is required. For example:

   AfxGetMainWnd()->PostMessage (WM_COMMAND, IDC_HOST_CHANGE);

In lieu of a registered message, this provides a clean separation between event generation by your application's innards and event handling by your application's user interface. /ravi

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[Gary R Wheeler]

Here's a quick, general introduction to user-defined messages. I'm assuming you're using MFC here. 1. Define a message identifier. You can base it off of WM_USER or WM_APP:

#define WM_MY_MESSAGE (WM_APP + 1)

2. Declare a message handler in your dialog class:

afx_msg LRESULT OnMyMessage(WPARAM wParam,LPARAM lParam);

3. Add an entry to the message map for your dialog class:

BEGIN_MESSAGE_MAP(...)
// ...
ON_MESSAGE(WM_MY_MESSAGE,OnMyMessage)
// ...
END_MESSAGE_MAP()

4. Define your message handler:

LRESULT MyDialogClass::OnMyMessage(WPARAM wParam,LPARAM lParam)
{
// ...
}

5. Finally, send the message when needed:

my_dialog->SendMessage(WM_MY_MESSAGE,
(WPARAM)first_parameter,
(LPARAM)second_parameter);

where first_parameter and second_parameter are whatever values you want to send with the message.

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