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Q82077: FIFLE: Sample Application Demonstrates Using DDEML

Article: Q82077
Product(s): Microsoft Windows Software Development Kit
Version(s): 3.0,3.1
Operating System(s): 
Keyword(s): kbfile kbsample kb16bitonly kbDDE kbGrpDSUser kbOSWin310 kbOSWin300 kbUser
Last Modified: 23-JUL-2001

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The information in this article applies to:

- Microsoft Windows Software Development Kit (SDK) versions 3.0, 3.1 
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SUMMARY
=======

Dmldemo.exe is a file in the Microsoft Download Center that demonstrates how two
applications for the Windows environment can communicate using the Dynamic Data
Exchange Management Libraries (DDEML). Dmldemo.exe demonstrates the following
types of transactions:

- Connect

- Request

- Asynchronous Request

- Hot Advise Loop

- Warm Advise Loop

NOTE: The DMLDEMO file contains code for a client application and for a server
application in separate directories. To preserve the directory structure, be
sure to specify the -d option when extracting the files. For example,

     dmldemo -d

MORE INFORMATION
================

The following file is available for download from the Microsoft Download
Center:

  Dmldemo.exe

For additional information about how to download Microsoft Support files, click
the article number below to view the article in the Microsoft Knowledge Base:

  Q119591 How to Obtain Microsoft Support Files from Online Services

Microsoft used the most current virus detection software available on the date of
posting to scan this file for viruses. Once posted, the file is housed on secure
servers that prevent any unauthorized changes to the file.

Transactions Types:

The remainder of this article details the five transaction types.

Connect Transaction
-------------------

The client calls the DdeConnect function to connect to the server and initiate a
conversation. In the DMLDEMO application, the DdeConnect function starts a
general conversation, which deals with text and bitmaps, and a SYSTEM
conversation, which supports the system topic.

Request Transaction
-------------------

When the client requires information from the server, the client calls the
DdeClientTransaction function, specifying XTYP_REQUEST as the value for the
uType parameter. The DMLDEMO client uses a request transaction to retrieve the
number and type of bitmaps to display. The request transaction is used in both
synchronous and asynchronous contexts.

Asynchronous Transaction
------------------------

The client starts an asynchronous transaction with the server to request
information that may not be ready at the time the client makes the request.

In the DMLDEMO application, the client starts an asynchronous transaction when
the user chooses Asynchronous Transaction from the Transactions menu. When the
server receives the request (as an XTYP_REQUEST transaction), it displays a
dialog box that asks the user how many copies of the window bitmap the client
should display. After the user dismisses the dialog box, the server returns a
data handle containing the number the user selected from its callback function.
When the server has completed the transaction, the DDEML sends an
XTYP_XACT_COMPLETE to the client application's callback function. The client
then displays the requested number of bitmaps.

In this case, an asynchronous transaction is required to prevent the transaction
from timing out before the user has a chance to close the dialog box.

Hot Advise Loop
---------------

When a hot advise loop is established between a client and a server, the server
notifies the client (through an XTYP_ADVDATA transaction) each time a certain
piece of data changes. The notification includes a handle to the changed data.
When a hot advise loop is active in the DMLDEMO application, the server notifies
the client that the bitmap has changed (this notification includes a handle to
the changed bitmap) every time the server's bitmap is changed. (To change the
bitmap, choose Change Bitmap from the server application's menu.) The client
application then displays the bitmap.

Warm Advise Loop
----------------

When a warm advise loop is established between a client and a server, the server
notifies the client that the specified data has changed, but the server does not
send the changed data to the client. In the DMLDEMO application, when the client
receives a notification from the server, the client brings up a message box
asking the user if the client's window should be updated with the new bitmap
from the server. If the user chooses the "Yes" button, the client requests the
changed bitmap from the server using the DdeClientTransaction function,
specifying XTYP_REQUEST as the value of the uType parameter.

Additional query words: DMLDEMO

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Keywords          : kbfile kbsample kb16bitonly kbDDE kbGrpDSUser kbOSWin310 kbOSWin300 kbUser 
Technology        : kbAudDeveloper kbWin3xSearch kbSDKSearch kbWinSDKSearch kbWinSDK300 kbWinSDK310
Version           : :3.0,3.1

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