Is it possible to scan barcodes into a process in the background? - io

Question

I'm making a gym management web app that handles sign-ins. Members have a barcode on a tag that they scan when they arrive to the gym.
I've heard that most barcode scanners simply act as a keyboard. This would require the scanning-in page to be open and in the foreground when a barcode is scanned.
If it's just a keyboard, how would I send the barcode scanner input to a single background process running on the computer, and have it ignore by all processes that may be in focus?

Answer 1

You're right that most scanner can support HID in keyboard emulation, but that's just the start.
If you want to have a bit more control over the data you can use a scanners that support the OPOS driver model.
Take a look at Zebra's Windows SDK to have a overview of the things that you can do. It may be a better solution than try to steal the barcode data coming in the OS as a keyboard entry to the foreground app.
Disclaimer: I work for Zebra Technologies
Other Barcode scanner vendor support a similar driver model.

Answer 2

I found an interesting post with a simple solution:
On the form constructor
InitializeComponent():
this.KeyPress += new System.Windows.Forms.KeyPressEventHandler(this.Form1_KeyPress);
Handler & supporting items:
DateTime _lastKeystroke = new DateTime(0);
List<char> _barcode = new List<char>(10);
private void Form1_KeyPress(object sender, KeyPressEventArgs e)
{
// check timing (keystrokes within 100 ms)
TimeSpan elapsed = (DateTime.Now - _lastKeystroke);
if (elapsed.TotalMilliseconds > 100)
_barcode.Clear();
// record keystroke & timestamp
_barcode.Add(e.KeyChar);
_lastKeystroke = DateTime.Now;
// process barcode
if (e.KeyChar == 13 && _barcode.Count > 0) {
string msg = new String(_barcode.ToArray());
MessageBox.Show(msg);
_barcode.Clear();
}
}
Credits: #ltiong_sh
Original post: Here

Answer 3

Use RawInput API (https://www.codeproject.com/Articles/17123/Using-Raw-Input-from-C-to-handle-multiple-keyboard#_Toc156395975) and check device ID for incoming keystrokes. Different devices have different IDs. You can also block keystrokes from scanner from reaching your application and interfering with input fields.
One thing you might want to add is option for user to identity which device is used as a barcode scanner. I did it by asking user to test-scan barcode with scanner on first application startup or in settings.
Works with any barcode scanner which outputs keystrokes.