Advanced MFC Programming

Chapter 16. Context Sensitive Help
Client Implementation
Sample 15.2\DDE\Client is implemented as a dialog based application using Application Wizard.
Similar to the server, here an edit control is included in the dialog template that will be used to display
DDE activities. The DDE initialization procedure is implemented in function
CDDEDialog::OnInitDialog(). There is also another edit box and a button labeled “Connect” in the dialog
box. When the user clicks this button, the application will retrieve the string from this edit box, use it as the
topic name and call function ::DdeConnect(…) to connect to the server:
……
void CDDECliDlg::OnButtonConnect()
{
if(m_hConvClient == 0)
{
UpdateData();
if(m_szTopic.IsEmpty())
{
AfxMessageBox("Please input a topic name!");
return;
}
m_hszTopicName=ObtainHsz(m_szTopic);
m_hConvClient=::DdeConnect
(
m_dwInst, m_hszServiceName, m_hszTopicName, (PCONVCONTEXT)NULL
);
if(m_hConvClient == FALSE)
{
UnobtainHsz(m_hszTopicName);
Printf("Unable to connect server!\r\n");
}
else Printf("Connected to server!\r\n");
m_btnConnect.SetWindowText("Disconnect");
}
}
The value returned by function ::DdeConnect(…) is a handle used for conversation. Every time the
client want to make a transaction to the server, it must present this handle. By using the handle, the server
knows with whom it is talking with.
In case the connection is not successful, function ::DdeConnect(…) will return a FALSE value.
Confirm Connection
On the server side, if the connection is successful, it will further receive an XTYP_CONNECT_CONFIRM
message from the client. In this case, apart from hszTopic and hszAppName parameters, hconv is also used
to provide the conversation handle that should be used by the server to make further conversation with the
client. The following code segment shows how this message is processed on the server side:
……
……
case XTYP_CONNECT_CONFIRM:
{
m_hConvServer=hConv;
Printf("Handle saved for conversation!\r\n");
return (HDDEDATA)NULL;
}
Variable m_hConvServer is a static variable declared in class CMainFrame and is initialized to NULL in
the constructor.
DDE Disconnection
After the connection is set up, the client and server can proceed to initiate various types of transactions.
We will show this in later sections. After all the transactions are finished, or if one side wants to exit, the
463