[AccessD] using the message class

John,
Thanks for always making your fine examples avaiable to us all. I really
appreciate it!

John B.


-----Original Message-----
From: accessd-bounces at databaseadvisors.com
[mailto:accessd-bounces at databaseadvisors.com] On Behalf Of jwcolby
Sent: Friday, January 23, 2009 12:01 AM
To: Access Developers discussion and problem solving
Subject: [AccessD] using the message class

I am building a system to process rather large files.  I 
export tables in SQL Server out to files, process the files 
via an address validation program, then process the files 
back into SQL Server.

One of the steps has to process every file in a directory. 
The code itself sits out in a function, which is called from 
a form.  The form allows me to select a from dir and to dir, 
then do the processing.

The functions can be called by hand from the debug window (I 
do this during debug, or from the click of a button on the 
form once things are working.

One way to feed the status back is to hard code the name of 
the form and control on the form that the status value is to 
go into, in this case the name of the file currently 
processing, and a line count mod 1000 kind of thing to show 
me every 1000th record processed.

Another way to do the status is to set up a message channel. 
    By passing in the name of the form, the function that 
iterates the directory can then broadcast a message with the 
"to" being the name of the form passed in, the subject being 
"FileName", and the message being the name of the file being 
processed.

The form sinks the message event and if the To matches 
me.name it processes the message.  If the Subj = "FileName", 
it takes the Message value and places it into 
txtFileName.Value, IOW it displays the message (the name of 
the file being processed) in a text box.

Likewise I have another function that actually processes 
each file.  It opens the file, reads line by line, massaging 
the data and writing the results out to another file.  It is 
helpful to be able to see the line number being processed 
every once in awhile to know that something is happening.

Again, that function simply calls the msg channel (class) 
every 1000th record and passes the record counter out.  It 
passes out the form name as the To, "RecordCnt" as the 
subject, and the count itself as the message.

Again, the form sinks the message event and if the To 
matches me.name it processes the message.  If the Subj = 
"RecordCnt", it takes the Message value and places it into 
txtRecordCnt.Value, IOW it displays the message (the current 
line count of the file being processed) in a text box.

Now obviously this can be done other ways, but the advantage 
of WithEvents is that the form does not have to be open, or 
for that matter even exist, and the code will still run. 
Messages are broadcast, and if the form happens to be open 
(trigggered the code to run) it can sink the messages and 
display the status.

This is an example of how I actually use my message class to 
broadcast status messages from code and display them in a form.

I can run the code by hand and because there is no hard 
coded form / control reference, the code runs just fine.  I 
can then tie the code to a specific form (or many different 
forms) and simply by passing in the form name the message 
can tell the form that the message is intended for it, and 
the form can process the message.

I am sitting here watching my code process about 85 
different files, displaying the file name and an 
incrementing line count, and it all took just a few minutes 
to set up the status display.

A single line of code in each of two functions, and an event 
sink in the form, about 12 lines of code.

Classes and withevents.

As I mentioned the message class is available for your 
enjoyment on my web site, along with a very simple demo to 
show you how to use it.
-- 
John W. Colby
www.ColbyConsulting.com
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