Change value of variable from another program?!!!!!!


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Thread: Change value of variable from another program?!!!!!!

  1. #1
    Jack Renold Guest

    Change value of variable from another program?!!!!!!


    I need to be able to change a value of a variable in my application from an
    other application that i have created. One application will sit on the users
    task bar making constant checks to a SQL Server database. if a value has
    changed in a particular table i want to tell the second application and update
    a variable.

    I could just make the second application to the checks to the database but
    that would mean both applications are doing the checking, which in turn could
    put alot of pressure on the database.

    Is there away of creating Environment variables that are global to both applications?
    Or is there another place i can write to in Windows? Maybe the registry.

    Any ideas

    Thanks

  2. #2
    Larry Rebich Guest

    Re: Change value of variable from another program?!!!!!!

    Jack:

    Some months ago I wrote a tip of the month that I call 'Send Text from One
    App to Another'. Link to http://www.buygold.net/tips then look for the
    December 2000 tip of the month. A sample program is provided. From the tip's
    intro:

    Thanks to Francesco Balena's article, Synchronize Your Apps, page 58, in the
    September 2000 issue of the Visual Basic Programmers Journal, I was able to
    develop a simple routine to allow communication between running
    applications. I added a few wrinkles and made this the tip-of-the-month.

    Cheers,
    Larry Rebich

    More tips link to:
    http://www.buygold.net/tips

    Please:
    No personal e-mail questions :-)

    "Jack Renold" <Renold_Jacks234@hotmail.com> wrote in message
    news:3dee0712$1@tnews.web.devx.com...
    >
    > I need to be able to change a value of a variable in my application from

    an
    > other application that i have created. One application will sit on the

    users
    > task bar making constant checks to a SQL Server database. if a value has
    > changed in a particular table i want to tell the second application and

    update
    > a variable.
    >
    > I could just make the second application to the checks to the database but
    > that would mean both applications are doing the checking, which in turn

    could
    > put alot of pressure on the database.
    >
    > Is there away of creating Environment variables that are global to both

    applications?
    > Or is there another place i can write to in Windows? Maybe the registry.
    >
    > Any ideas
    >
    > Thanks




  3. #3
    Russ Holsclaw Guest

    Re: Change value of variable from another program?!!!!!!

    > I need to be able to change a value of a variable in my application from
    an
    > other application that i have created. One application will sit on the

    users
    > task bar making constant checks to a SQL Server database. if a value has
    > changed in a particular table i want to tell the second application and

    update
    > a variable.
    >
    > I could just make the second application to the checks to the database but
    > that would mean both applications are doing the checking, which in turn

    could
    > put alot of pressure on the database.
    >
    > Is there away of creating Environment variables that are global to both

    applications?
    > Or is there another place i can write to in Windows? Maybe the registry.


    There are a number of options here, as you've evidently surmised. One you
    didn't mention is Dynamic Data Exchange, or DDE, which is a messaging
    protocol supported by Windows that is specifically designed to make one
    application aware of changing data values in another.

    The DDE mechanism is associated with forms and controls, permitting
    applications to exchange commands and data with each other that are tied to
    the contents of individual controls.

    Read the writeups on the various properties, methods and events with names
    beginning with "Link" in the VB Reference.

    I gather that Microsoft has de-emphasized its use in recent years, but it's
    still supported by Windows, and VB, at least for the immediate future. I
    haven't looked to see if it's still there in the .NET world. I notice that
    there does not appear to be a writeup on DDE in the VB6 Programmer's Guide
    anymore, only in the Reference Guide, so a nice introductory writeup doesn't
    seem to be included in the latest MSDN docs. That seems to suggest that MS
    may eventually phase out support. I'm not clear on what

    You should also look into creating an interface between the applications by
    implementing the second, "background" application as an out-of-process
    ActiveX server. It could notify your "foreground" application raising
    Events.

    By the way, I wouldn't recommend having a program in a continuous loop
    constantly querying an SQL database, at least not without regulating the
    frequency of checking through the use of a Timer. (A few years ago, I worked
    with a programming team that adopted the term "Prairie-Dog Interface" to
    describe methods of polling files and databases looking for updates. -- I
    live in Boulder, Colorado, so this is a metaphor referencing the known
    behavior patterns of the little rodents, who are constantly sticking their
    noses out of their burrows checking on current conditions.) Any mechanism
    you can use wherein one process receives a direct notification of updates
    via a message is preferable to the Prairie-Dog method, which should only be
    used if there is no direct message-sending mechanism readily available.


  4. #4
    Phil Weber Guest

    Re: Change value of variable from another program?!!!!!!

    > I gather that Microsoft has de-emphasized its use in recent
    > years, but it's still supported by Windows, and VB, at least for
    > the immediate future. I haven't looked to see if it's still there
    > in the .NET world.


    Russ: FYI, VB.NET does not support DDE.
    --
    Phil Weber



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