Develop Reference

C# how to detect which keyboard is pressed? [duplicate]

I have a barcode scanner (which acts like a keyboard) and of course I have a keyboard too hooked up to a computer. The software is accepting input from both the scanner and the keyboard. I need to accept only the scanner's input. The code is written in C#. Is there a way to "disable" input from the keyboard and only accept input from the scanner?
Note:
Keyboard is part of a laptop...so it cannot be unplugged. Also, I tried putting the following code
protected override Boolean ProcessDialogKey(System.Windows.Forms.Keys keyData)
{
return true;
}
But then along with ignoring the keystrokes from the keyboard, the barcode scanner input is also ignored.
I cannot have the scanner send sentinal characters as, the scanner is being used by other applications and adding a sentinal character stream would mean modifying other code.
Also, I cannot use the timing method of determining if the input came from a barcode scanner (if its a bunch of characters followed by a pause) since the barcodes scanned could potentially be single character barcodes.
Yes, I am reading data from a stream.
I am trying to follow along with the article: Distinguishing Barcode Scanners from the Keyboard in WinForms. However I have the following questions:
I get an error NativeMethods is inaccessible due to its protection level. It seems as though I need to import a dll; is this correct? If so, how do I do it?
Which protected override void WndProc(ref Message m) definition should I use, there are two implementations in the article?
Am getting an error related to [SecurityPermission( SecurityAction.LinkDemand, Flags = SecurityPermissionFlag.UnmanagedCode)] error CS0246: The type or namespace name 'SecurityPermission' could not be found (are you missing a using directive or an assembly reference?). How do I resolve this error?
There is also an error on the line containing: if ((from hardwareId in hardwareIds where deviceName.Contains(hardwareId) select hardwareId).Count() > 0) Error is error CS1026: ) expected.
Should I be placing all the code in the article in one .cs file called BarcodeScannerListener.cs?
Followup questions about C# solution source code posted by Nicholas Piasecki on http://nicholas.piasecki.name/blog/2009/02/distinguishing-barcode-scanners-from-the-keyboard-in-winforms/:
I was not able to open the solution in VS 2005, so I downloaded Visual C# 2008 Express Edition, and the code ran. However, after hooking up my barcode scanner and scanning a barcode, the program did not recognize the scan. I put a break point in OnBarcodeScanned method but it never got hit. I did change the App.config with the id of my Barcode scanner obtained using Device Manager. There seems to be 2 deviceNames with HID#Vid_0536&Pid_01c1 (which is obtained from Device Manager when the scanner is hooked up). I don't know if this is causing the scanning not to work. When iterating over the deviceNames, here is the list of devices I found (using the debugger):
"\??\HID#Vid_0536&Pid_01c1&MI_01#9&25ca5370&0&0000#{4d1e55b2-f16f-11cf-88cb-001111000030}"
"\??\HID#Vid_0536&Pid_01c1&MI_00#9&38e10b9&0&0000#{884b96c3-56ef-11d1-bc8c-00a0c91405dd}"
"\??\HID#Vid_413c&Pid_2101&MI_00#8&1966e83d&0&0000#{884b96c3-56ef-11d1-bc8c-00a0c91405dd}"
"\??\HID#Vid_413c&Pid_3012#7&960fae0&0&0000#{378de44c-56ef-11d1-bc8c-00a0c91405dd}"
"\??\Root#RDP_KBD#0000#{884b96c3-56ef-11d1-bc8c-00a0c91405dd}"
"\??\ACPI#PNP0303#4&2f94427b&0#{884b96c3-56ef-11d1-bc8c-00a0c91405dd}"
"\??\Root#RDP_MOU#0000#{378de44c-56ef-11d1-bc8c-00a0c91405dd}"
"\??\ACPI#PNP0F13#4&2f94427b&0#{378de44c-56ef-11d1-bc8c-00a0c91405dd}"
So there are 2 entries for HID#Vid_0536&Pid_01c1; could that be causing the scanning not to work?
OK so it seems that I had to figure out a way to not depend on the ASCII 0x04 character being sent by the scanner...since my scanner does not send that character. After that, the barcode scanned event is fired and the popup with the barcode is shown. So thanks Nicholas for your help.

You could use the Raw Input API to distinguish between the keyboard and the scanner like I did recently. It doesn't matter how many keyboard or keyboard-like devices you have hooked up; you will see a WM_INPUT before the keystroke is mapped to a device-independent virtual key that you typically see in a KeyDown event.
Far easier is to do what others have recommended and configure the scanner to send sentinel characters before and after the barcode. (You usually do this by scanning special barcodes in the back of the scanner's user manual.) Then, your main form's KeyPreview event can watch those roll end and swallow the key events for any child control if it's in the middle of a barcode read. Or, if you wanted to be fancier, you could use a low-level keyboard hook with SetWindowsHookEx() to watch for those sentinels and swallow them there (advantage of this is you could still get the event even if your app didn't have focus).
I couldn't change the sentinel values on our barcode scanners among other things so I had to go the complicated route. Was definitely painful. Keep it simple if you can!
--
Your update, seven years later: If your use case is reading from a USB barcode scanner, Windows 10 has a nice, friendly API for this built-in in Windows.Devices.PointOfService.BarcodeScanner. It's a UWP/WinRT API, but you can use it from a regular desktop app as well; that's what I'm doing now. Here's some example code for it, straight from my app, to give you the gist:
{
using System;
using System.Linq;
using System.Threading.Tasks;
using System.Windows;
using Windows.Devices.Enumeration;
using Windows.Devices.PointOfService;
using Windows.Storage.Streams;
using PosBarcodeScanner = Windows.Devices.PointOfService.BarcodeScanner;
public class BarcodeScanner : IBarcodeScanner, IDisposable
{
private ClaimedBarcodeScanner scanner;
public event EventHandler<BarcodeScannedEventArgs> BarcodeScanned;
~BarcodeScanner()
{
this.Dispose(false);
}
public bool Exists
{
get
{
return this.scanner != null;
}
}
public void Dispose()
{
this.Dispose(true);
GC.SuppressFinalize(this);
}
public async Task StartAsync()
{
if (this.scanner == null)
{
var collection = await DeviceInformation.FindAllAsync(PosBarcodeScanner.GetDeviceSelector());
if (collection != null && collection.Count > 0)
{
var identity = collection.First().Id;
var device = await PosBarcodeScanner.FromIdAsync(identity);
if (device != null)
{
this.scanner = await device.ClaimScannerAsync();
if (this.scanner != null)
{
this.scanner.IsDecodeDataEnabled = true;
this.scanner.ReleaseDeviceRequested += WhenScannerReleaseDeviceRequested;
this.scanner.DataReceived += WhenScannerDataReceived;
await this.scanner.EnableAsync();
}
}
}
}
}
private void WhenScannerDataReceived(object sender, BarcodeScannerDataReceivedEventArgs args)
{
var data = args.Report.ScanDataLabel;
using (var reader = DataReader.FromBuffer(data))
{
var text = reader.ReadString(data.Length);
var bsea = new BarcodeScannedEventArgs(text);
this.BarcodeScanned?.Invoke(this, bsea);
}
}
private void WhenScannerReleaseDeviceRequested(object sender, ClaimedBarcodeScanner args)
{
args.RetainDevice();
}
private void Dispose(bool disposing)
{
if (disposing)
{
this.scanner = null;
}
}
}
}
Granted, you'll need a barcode scanner that supports the USB HID POS and isn't just a keyboard wedge. If your scanner is just a keyboard wedge, I recommend picking up something like a used Honeywell 4600G off eBay for like $25. Trust me, your sanity will be worth it.

What I did in a similar situation is distinguish between a scan and a user typing by looking at the speed of the input.
Lots of characters very close together then a pause is a scan. Anything else is keyboard input.
I don't know exactly your requirements, so maybe that won't do for you, but it's the best I've got :)

It depends on the way you are interacting with the device. Anyway it wont be a C# solution, it will be some other library. Are you reading data from a stream? If you are just taking keystrokes, there may be nothing you can do about it.

I know this is an old thread, found it by searching barcode scanning in WIN10.
Just a few notes in case someone needs it.
These scanners from Honeywell have several USB interfaces.
One is a keyboard + Hid Point of sales (composite device).
Also there are CDC-ACM (ComPort emulation) and Hid Point of sales (alone) + more.
By default the scanners expose a serial number, so the host can distinguish between many devices (I had once +20 connected). There is a command to disable the serial number though!
The newer models behave the same in this regard.
If you want to see it live, try my terminal program yat3 (free on my site).
It can open all the interfaces mentioned above and is tailored for such devices.
A word to use keyboard interfaces:
Only use them as a last resort. They are slow, less reliable when it comes to exotic characters. The only good use is if you want to enter data into existing applications. If you code anyway, then reading from ComPort/HidPos-Device is easier.

look at this: http://nate.dynalias.net/dev/keyboardredirector.rails (NOT AVAILABLE ANYMORE) works great!
Specify the keyboard and the keys you want to block, and it works like a charm!
Also take a look at this: http://www.oblita.com/interception.html
You can create a C# wrapper for it - it also works like a charm..

I think you might be able to distinguish multiple keyboards through DirectX API, or if that doesn't work, through raw input API.

I have successfully accomplished what you folks are looking for here. I have an application that receives all barcode character data from a Honeywell/Metrologic barcode scanner. No other application on the system receives the data from the scanner, and the keyboard continues to function normally.
My application uses a combination of raw input and the dreaded low-level keyboard hook system. Contrary to what is written here, I found that the wm_input message is received before the keyboard hook function is called. My code to process the wm_input message basically sets a boolean variable to specify whether or not the received character is from the scanner. The keyboard hook function, called immediately after the wm_input is processed, swallows the scanner’s pseudo-keyboard data, preventing the data from being received by other applications.
The keyboard hook function has to be placed in an dll since you want to intercept all system keyboard messages. Also, a memory mapped file has to be used for the wm_input processing code to communicate with the dll.

Unity3D KeyCode.Home issue?

Hello i have a line of code that should quit the game upon pressing the three hardware button on the bottom like Menu, Home, Back
it seems that the back and the home only is working but the menu is not working
I have a Xiaomi Redmi Note 4X phone, how am i suppose to fix this issue?
Is it the same "Menu" as the other phone where when you press it, it'll show list of the opened app
here's the code:
if (Input.GetKey (KeyCode.Home) || Input.GetKey (KeyCode.Escape) || Input.GetKey (KeyCode.Menu))
{
Save ();
System.Diagnostics.Process.GetCurrentProcess ().Kill ();
}

Is it the same "Menu" as the other phone where when you press it,
it'll show list of the opened ap
Yes.
I have a Xiaomi Redmi Note 4X phone, how am i suppose to fix this
issue?
It should work otherwise it is a bug and you should file for a bug request. Before you file for abug request, use the script below to make that the Menu key is not mapped to another key.
public class KeyCodeFinder : MonoBehaviour
{
public Text text;
Array allKeyCodes;
void Start()
{
allKeyCodes = System.Enum.GetValues(typeof(KeyCode));
}
void Update()
{
foreach (KeyCode tempKey in allKeyCodes)
{
if (Input.GetKeyDown(tempKey))
{
text.text = "Pressed: KeyCode." + tempKey;
Debug.Log("Pressed: KeyCode." + tempKey);
}
}
}
}
Meanwhile, you can make a Java plugin that calls your C# function when the Menu keycode is pressed. That's another option you have.

Those buttons are OS related, you don't really control what happens with those. Well, you can track them and kill your app but this is going against what every single application does. That is, if you press the back or home or quit, it gets back to the main OS page, but your app is still on the stack ready to get back.
If you want to save when the user quits, maybe you want to look into
https://docs.unity3d.com/ScriptReference/MonoBehaviour.OnApplicationPause.html
This will make your app behave in a more common way.
On a side note, I would even assume this kind of attempt to over control the app would be rejected for AppStore (iOS) as it would not comply with their generic requirements.

It is allways possible to map a custom KeyCode that is not mapped so far.
First find out what keycode the key has
Event e = Event.current;
if (e.isKey)
{
Debug.Log("Detected key code: " + e.keyCode);
}
Let's say this gives you 10 as keycode (a one that is not mapped in Unities KeyCode so far)
You can than simply define a new one like
KeyCode MY_HOME_BUTTON = (KeyCode) 10;
and than use it like
if(Input.MY_HOME_BUTTON)
{
...
}
If it is completely possible to catch the home button depends on the OS (most of the time those buttons cannot be catched by an app but are handled by the OS first)

Writing to textbox inside an unselected tab

I have a program that can read and write on serial, GPIB, USB, and Ethernet. It has a tab for each method of communication with a textbox inside that displays communication on the port. One of the tabs is listed as All Comms and that text box has data from all communication methods. I am currently working on the serial port portion of the code and my program keeps freezing. Half the time I run my code it functions without issue writing to both tabs. The other half it freezes up when it tries to write to the text box inside the tab that is not selected(found by stepping through the code a line at a time).
I pulled the text boxes outside the tab control and this fixes the freezing issue. When the program freezes it does not display an error message and does not crash so no crash report(left it running over the weekend and it never finished crashing).
I would think that I need to select the other tab and then write to it, but why would the code work correctly half the time I run it?
Image of the program
private void serialPort1_DataReceived(object sender, System.IO.Ports.SerialDataReceivedEventArgs e)
{
rxString = rxString + serialPort1.ReadExisting();
if (rxString == "\b")
{
//Removes 1 character when backspace is the key pressed
rxSerialTextBox.ReadOnly = false;
rxSerialTextBox.Select(rxSerialTextBox.TextLength - 1, rxSerialTextBox.TextLength);
rxSerialTextBox.SelectedText = String.Empty;
rxSerialTextBox.ReadOnly = true;
rxString = "";
}
while (rxString.Length != 0)
{
try
{
while (rxString.Length != 0)
{
if (rxString.IndexOf("\r\n") == 0)
{
//Adds a newline when newline is the next characters in the string
rxString = rxString.Substring(rxString.IndexOf("\r\n") + 2);
rxAllCommsTextBox.AppendText(Environment.NewLine);
rxSerialTextBox.AppendText(Environment.NewLine);
}
//Adds a new character to the text box
rxAllCommsTextBox.AppendText(rxString.Substring(0, 1));
rxSerialTextBox.AppendText(rxString.Substring(0, 1));
rxString = rxString.Substring(1, rxString.Length - 1);
}
}
catch
{
//rxString = "";
}
}
}

A quck look at the SerialPort.DataReceived event documentation brings into attention the following Remarks section paragraph:
The DataReceived event is raised on a secondary thread when data is received from the SerialPort object. Because this event is raised on a secondary thread, and not the main thread, attempting to modify some elements in the main thread, such as UI elements, could raise a threading exception. If it is necessary to modify elements in the main Form or Control, post change requests back using Invoke, which will do the work on the proper thread.
According to this, your code that touches UI elements (text boxes) inside that event handler is incorrect. What the documentation doesn't say is that when you do so, the behavior is undefined - sometimes it may work, another time hang, yet another time throw exception.
So, instead of asking why your incorrect code sometimes work, you'd better concentrate on making it correct, and only then if something is not working, ask why and seek for a solution.
P.S. I'm not going to address how the concrete issue can be solved - there are a tons of posts, explanations and examples of how to marshal the calls to the UI thread, and in that regard there is nothing special in your case.

It was a little confusing your question ...
you can try, it is understood correctly, try to keep the value you want to assign the memory context, and assign the value based on another type of iteration.
At the moment the application freezes, which shows the breakpoint? The expected behavior does it work?
I would try a configuration object, such as a list, with various configurations, and certain state, the amount you need to pass the list to the tabcontrol. Obviously, it needs to check what's not working and why is not ...

Monitoring keyboard activity in C# while my application is in the background

First of all I need to make it clear that I have no interest in keylogging.
I need a way to monitor keyboard activity at the most basic level while my application is in the background.
I don't need to know which keys, I don't need to save any data, I don't need or plan to hide my application at all, all I need is to know when keys are pressed and invoke a method.
I'm looking for the simplest way to do this possible, I know a reasonable amount of C# but nothing too complex as most of my knowledge is self-taught.
I've looked around for some appropriate ways of doing this and I've found nothing useful. All I've found is a bunch of people saying "No, that's illegal" on forums and source code for in depth keyloggers.
If any of you could advise me on a way to achieve this then I would be most appreciative.

You'll need to use Window Hooks:
Low-Level Keyboard Hook in C#
But beware, Windows security, may be protecting us from doing what you want!

You can monitor keyboard and mouse activity in the background with the Nuget package MouseKeyHook (GitHub).
This code detects when a key is pressed:
private IKeyboardMouseEvents _globalHook;
private void Subscribe()
{
if (_globalHook == null)
{
// Note: for the application hook, use the Hook.AppEvents() instead
_globalHook = Hook.GlobalEvents();
_globalHook.KeyPress += GlobalHookKeyPress;
}
}
private static void GlobalHookKeyPress(object sender, KeyPressEventArgs e)
{
Console.WriteLine("KeyPress: \t{0}", e.KeyChar);
}
private void Unsubscribe()
{
if (_globalHook != null)
{
_globalHook.KeyPress -= GlobalHookKeyPress;
_globalHook.Dispose();
}
}
You will need to call Subscribe() to start listening, and Unsubscribe() to stop listening. Obviously you need to modify GlobalHookKeyPress() to do useful work.
I needed this functionality in order to write a utility which will turn on the keyboard backlight on a Lenovo Thinkpad when any key is pressed, including CTRL (which KeyPress doesn't catch). For this purpose, I had to monitor for key down instead. The code is the same except we attach to a different event...
_globalHook.KeyDown += GlobalHookOnKeyDown;
and the event handler signature is different:
private static void GlobalHookOnKeyDown(object sender, KeyEventArgs e)
{
Console.WriteLine("KeyDown: \t{0}", e.KeyCode);
}
The library can also detect specific key combinations and sequences. For example:
Hook.GlobalEvents().OnCombination(new Dictionary<Combination, Action>
{
{ Combination.TriggeredBy(Keys.A).Control(), () => { Console.WriteLine("You Pressed CTRL+A"); } },
{ Combination.FromString("Shift+Alt+Enter"), () => { Console.WriteLine("You Pressed FULL SCREEN"); } }
});

Microsoft tells you How to: Handle Keyboard Input at the Form Level. As long as you handle the same event(s) this works for any non web application.
You should also take a look at the other questions here on SO, such as Handling Input from a Keyboard Wedge

You could register Windows Hot Key with RegisterHotKey windows API, look at this blog post :
http://www.liensberger.it/web/blog/?p=207

MC75 Barcode Reader Issue

I am aiding in the development for a custom made application for the Motorola MC75. It is well tuned except for a random bug with the barcode reader. Periodically, the barcode reader will only activate (start a read) if the right shoulder button is pressed. The middle and left shoulder buttons somehow become disabled. This is a unique bug in that it happens randomly and only effects 2 of the three buttons. The EMDK enables all buttons simultaneously so I am clueless as to where this is coming from (Internal or code related). If anyone has any input or advice please let me know and thank you beforehand.
Thanks,
Zach

I've worked with the Motorola EMDK before on the MC55. I'm not sure why the buttons are being disabled, and since you posted this in June you probably don't need the answer anymore, but here's a possible workaround:
Instead of letting the EMDK handle the triggers on its own, you can capture all triggers by setting up an event:
// Create a trigger device to handle all trigger events of stage 2 (pressed) or RELEASED
var device = new TriggerDevice(TriggerID.ALL_TRIGGERS, new[] { TriggerState.RELEASED, TriggerState.STAGE2 });
var trigger = new Trigger(device);
trigger.Stage2Notify += OnTrigger;
Then, in your OnTrigger method, you can handle the trigger and perform the appropriate action. For example, you can activate your barcode reader when any trigger is pressed:
private void OnTrigger(object sender, TriggerEventArgs e)
{
if (e.NewState == e.PreviousState)
return;
// Pseudocode
if (e.NewState == TriggerState.RELEASED)
{
myBarcodeReader.Actions.ToggleSoftTrigger();
myBarcodeReader.Actions.Flush();
myBarcodeReader.Actions.Disable();
}
else if (e.NewState == TriggerState.STAGE2)
{
// Prepare the barcode reader for scanning
// This initializes various objects but does not actually enable the scanner device
// The scanner device would still need to be triggered either via hardware or software
myBarcodeReader.Actions.Enable();
myBarcodeReader.Actions.Read(data);
// Finally, turn on the scanner via software
myBarcodeReader.Actions.ToggleSoftTrigger();
}
}