Exclusive access to barcode reader C#

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Hello guys, i have a situation where i would like to use barcode scanner exclusively using c#, i have a USB barcode scanner i want it to scan barcode behind the scene and print barcode anywhere the cursor is with some additional information with barcode.

Flow : barcode scanner scans barcode -> barcode gets searched in db to get info -> barcode + info gets printed in any active editor on screen.

For e.g.

DAP-11002233:testinformation

Hope i explained well.

thanks.

What I have tried:

i tried with low level keyboard hooks but it still prints barcode, also barcode is configured with enter key at the end but i am unable to manipulate it.

Posted 9-Aug-21 1:56am

Arsalan Khan 2

Updated 9-Aug-21 5:15am

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Richard MacCutchan 9-Aug-21 9:07am

"i want it to scan barcode behind the scene"
How would that work? A barcode scanner needs a human to point it at the barcode.

OriginalGriff 9-Aug-21 11:16am

Not all of them - some sit there passively scanning 24/7 or are activated by a product breaking a photocell beam.

Richard MacCutchan 9-Aug-21 11:22am

I doubt that the OP is using one of that type.

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OriginalGriff · Answer 1 · 2021-08-09T05:15:00

Solution 1

The problem is that USB scanners are generally shipped set to emulate a keyboard - and once any character of the code has been received nothing in the system (including the operating system itself) has any idea if it was typed or scanned.

It may be possible to program the code reader to produce unique "lead in" and "tail out" sequences so that code can "recognise" a scanned code and divert it somewhere, but to do that you would need to write a global hook that intercepts the keyboard, looks for the lead in, code, tail out sequence and passes it to a specific application for processing. And those in C# are definitely not a job for the inexperienced as a single slip can crash out your whole computer. Develop these in a VM or get used to frequent reboots or even reinstalling the OS ... :laugh:

Chances are, you're overthinking your application and should reconsider exactly what you are trying to accomplish. Installing global hooks isn't easy on production machines, and is likely to become harder in future to reduce the impact of key loggers and such like.

Posted 9-Aug-21 5:15am

OriginalGriff

Comments

Dave Kreskowiak 9-Aug-21 11:26am

Global keyboard hook? Damn! I must have gone overboard when I did this 15 years ago, using nothing but the form's KeyPreview and KeyDown event.

...and the scanners ability to be told what lead-in and out sequences to use.

OriginalGriff 9-Aug-21 12:37pm

That works, but only if the app is the active one.
The way I read the question, he's talking about "any active" on the screen - which means global hooking.

Dave Kreskowiak 9-Aug-21 13:06pm

I was thinking more like the "background" of his app, but yeah.

He needs to be more specific.

Arsalan Khan 2 10-Aug-21 3:41am

yes you are right i need the output in any active editor on screen, but with additional info with barcode, is there any way we can catch barcode scanner datarecieved event or something like that?

Dave Kreskowiak 10-Aug-21 9:28am

If this is a "keyboard wedge" scanner there are no events. The scanner acts just like a normal keyboard, typing whatever code it scans. The only events you get are the normal keyboard events, KeyDown, KeyUp, KeyPressed. There is no way for you to tell the difference between what is typed at the keyboard and what is typed by the scanner.

Arsalan Khan 2 10-Aug-21 3:44am

no i can not use suffix and prefix in the barcode scanner that is not requirment, barcode scanner is programmed with enter key at the end and we need to trigger something in between barcode and enter key so i m looking for some help if i can manage it through windows events or any thing which could help.

Dave Kreskowiak 10-Aug-21 9:31am

Without the prefix/postfix abilities, you have no way of telling what is typed by the user and what is typed by the scanner.

At least with a scanner with these abilities, you can watch for certain key strokes you normally wouldn't be able to type at the keyboard to tell you a barcode is coming and when it stops.

"that is not a requirement" IS a requirement if you have to do something when the barcode is scanned.

OriginalGriff 10-Aug-21 9:51am

I suspect that translates into "I don't know how to use a prefix / suffix" :sigh:

Dave Kreskowiak 10-Aug-21 10:15am

I'll give him a small benefit of doubt and guess it means a scanner off of AliExpress with no documentation. :)

OriginalGriff 10-Aug-21 10:25am

Oh, right. So no problem then - it'll be broken and useless within the week anyway ... :laugh:

PIEBALDconsult 9-Aug-21 12:52pm

Or a service, in the background.

Dave Kreskowiak 9-Aug-21 13:07pm

Keyboard input won't go to the service desktop, so that doesn't work.

Of course, this is assuming a keyboard wedge scanner...

I've dealt with ethernet-based scanners before where a service could easily get at it.

PIEBALDconsult 9-Aug-21 13:31pm

I've mostly interfaced with serial (RS-232 etc.) devices, so my knowledge is way out of date. I definitely would not recommend using a device which can only squirt bytes into the keyboard buffer -- that way madness lies.

Dave Kreskowiak 9-Aug-21 13:34pm

They're pretty easy to work with, so long as you understand how to handle keyboard events and focus in your app.

Personally, I like the ethernet variety better. You get more options on scanner placement away from the PC doing the work.

Arsalan Khan 2 10-Aug-21 3:38am

yes i would need background windows service

OriginalGriff 10-Aug-21 3:49am

You can't direct keyboard input to a service at all. A service cannot have any interaction with the user: input or output.

Which means that your scanner cannot be set to provide input as a keyboard device (with or without lead in and tailk out sequences). You will need to talk to your scanner manufacturer and either change the way it works, or find a scanner that provides a serial or ethernet connection.