Advanced MFC Programming

Chapter 16. Context Sensitive Help
}
XTYP_ADVSTOP,
5000,
NULL
);
if(hData != FALSE)
{
m_btnAdvise.SetWindowText("Advise");
m_bAdvise=FALSE;
}
}
UnobtainHsz(hszTextItem);
On the server side, after receiving this message, it simply turns off CMainFrame::m_bAdvise flag. After
this, if the user updates variable CMainFrame::m_szText, function ::DdePostAdvise(…) will not be called.
15.5 Transactions: Poke and Execute
Sample 15.5\DDE\Server and 15.5\DDE\Client are based on sample 15.4\DDE\Server and
15.4\DDE\Client respectively.
The poke transaction is the opposite of request transaction: the client can use this transaction to send
data to the server. The transaction is relatively simple: the client initiates the transaction by sending a
message along with the data handle to the server. After the server receives the message, it can obtain the
data from the data handle.
Like require and advise transactions, poke transaction also needs a topic name and an item name. In
the samples contained in 15.5\DDE\, a new item “Poke” is supported by both the server and the client.
Also, a new edit box and a new button labeled “Poke” are added to the client dialog box (see Figure 15-5).
The user can input any string into the edit box, and use poke transaction to send it to the server.
Poke Transaction: Client Side
Figure 15-5. New controls are added for “poke” and “execute”
transactions
The procedure of preparing data and calling function ::DdeClientTransaction(…) is very similar to
that of request transaction. The difference between two types of transactions is that here it is the client that
needs to prepare the data handle. In sample 15.5\DDE\Client, the user can input any string into the edit box
and send it to the server.
By now when sending data between two DDE applications, we always use data handle. An alternate
way of sending data is to use a pointer that contains the address to the data buffers. (The samples contained
in 15.5\DDE use data handle. We will see an example using pointer to transfer data in a later section).
When the client calls function ::DdeClientTransaction(…), the first parameter can be set to either a string
handle or a string pointer. If it is string handle, the second parameter must be 0xFFFFFFFF. If the first
parameter is a string pointer, the second parameter must specify the length of the buffers.
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