Dynamic Data Exchange Demos

                             Horizon Technologies Inc.


            Overview:

            The Dynamic Data Exchange (DDE) demo programs illustrate the
              concept of inter-program communications in a Microsoft
              Windows environment.  Source code for three programs is
              included.  All interactions between these programs are
              accomplished via the process of message passing in
              accordance with the DDE protocol defined by Microsoft.  A
              dynamic link library, DDELIB, developed by Horizon
              Technologies Inc., has been utilized in each of these
              programs to significantly reduce development time and
              program complexity.  The following material builds upon
              the information presented in the Overview of the  DDELIB
              documentation.


            AccExcel:


            ACCEXCEL is a menu driven application that shows the basics
              of a DDE connection to EXCEL.  EXCEL is a popular Windows
              spreadsheet application written by Microsoft.  The
              ACCEXCEL pull-down menu "DDE" lists four items; Initiate,
              Poke, Advise and Terminate.

            Initiate will establish a DDE session with a spreadsheet in
              EXCEL.  The name of the spreadsheet is entered into a
              dialog box presented by ACCEXCEL.  Poke will send data to
              the spreadsheet.  A dialog box will allow the
              specification of the cell range and the comma separated
              data values.  Advise will set up an advise circuit with a
              cell range in EXCEL.  When any data is modified in this
              range, EXCEL will advise ACCEXCEL which in turn will
              display a message box with the modified data.  Terminate
              simply closes the DDE session established with Initiate.


            Sub:


            SUB is a DDE client application that talks to the server
              application FISH.  FISH, supplied by Microsoft, displays
              fish swimming in a tank.  When FISH establishes a session
              with a client, it reveals a yellow submarine.  This
              submarine can then be manipulated by the client to move
              up, down, left, right and even fire a torpedo.  To
              augment this capability, the client can also obtain the
              current position of a fish in x,y coordinates.  With a
              simple sneak-up-from-behind-and-fire strategy, SUB easily
              controls the submarine in a mission to liquidate fish.

            Dynamic Data Exchange Demos - Copyright (C) 1990 Horizon
              Technologies Inc.  All rights reserved.  (517) 347-0800
                                       1



            Technically, SUB initiates two sessions with fish;  one for
              sub control and reporting, the other for fish position
              monitoring.  A DDE advise circuit for fish number zero is
              established.  The callback routine Fish() is called by
              DDELIB every time the fish moves.  In this routine, a
              request for the current sub position is made.  This
              results in a callback to the Sub() routine.  Once the
              current fish and sub positions are known, a call to
              MoveSub() is made.  Here, a command is sent to the sub
              for positioning and firing.  Note that the sub must be
              moving up or down, left or right.  Therefore, if the sub
              needs to maintain elevation, it must oscillate up and
              down.


            Session and SessUtil:


            SESSION is a DDE server application that provides a means
              for clients to store and retrieve string variable
              contents by name.  SESSION accepts DDE pokes, requests,
              and advises.  Commands are not supported.

            SESSION accomplishes this by registering the topic
              Variables.  The callback routine Session() is invoked by
              DDELIB every time a new client establishes a session,
              terminates a session, pokes or requests data, establishes
              an advise circuit, or sends a command.  SESSION processes
              these events to provide its services, such as saving the
              contents of a poke or advising a client of a change in
              the variable.

            SESSUTIL is a DDE client application that communicates with
              the SESSION application.  SESSUTIL shows the current
              contents of the User variable, as provided by SESSION, on
              its client area.  The user can set the contents of the
              User variable by selecting the Modify item from the File
              menu.  The new value is displayed on every instance of
              SESSUTIL running.

            SESSUTIL initially establishes a DDE advise circuit with
              SESSION on the variable User.  This causes the callback
              routine User() to be invoked by DDELIB whenever SESSION
              performs an advise.  User() will update its own copy of
              the value and then force a repaint of the client area,
              resulting in the new value of the User variable to be
              displayed.  When the user selects OK from the modify
              dialog box, the Poke() routine is called.  This sends the
              new variable to SESSION, which in turn advises SESSUTIL,
              which then displays the new value.

            Microsoft Word for Windows can eavesdrop in on the
              conversation, displaying the current contents of the User
              variable.  Simply insert a field of the form {ddeauto
              SESSION Variables User}.

            Dynamic Data Exchange Demos - Copyright (C) 1990 Horizon
              Technologies Inc.  All rights reserved.  (517) 347-0800
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