Develop Reference

C# BarCode Scanning Program won't Accept Alphabetic Characters

I've some code written in C# that allows the user to scan a barcode, and the label.Text changes to the input of the barcode. I used a label instead of textbox to prevent the user from fat-fingering a wrong barcode -basically disabling any keyboard input.
Everything works nice, except when the barcode being scanned has alphabetic characters in it. If the barcode starts with an alphabetic character and ends with an alphabetic character, then the barcode doesn't scan at all.
If the barcode starts with an alphabetic character, but ends with numeric characters, the program picks up only the trailing numeric characters.
Here's the code:
char cforKeyDown = '\0';
int _lastKeystroke = DateTime.Now.Millisecond;
List<char> _barcode = new List<char>();
bool UseKeyboard = false;
private void Form1_Load(object sender, EventArgs e)
{
this.ActiveControl = label1;
this.KeyDown += new KeyEventHandler(Form1_KeyDown);
this.KeyUp += new KeyEventHandler(Form1_KeyUp);
}
private void Form1_KeyUp(object sender, KeyEventArgs e)
{
// if keyboard input is allowed to read
if (UseKeyboard && e.KeyData != Keys.Enter)
{
MessageBox.Show(e.KeyData.ToString());
}
/* check if keydown and keyup is not different
* and keydown event is not fired again before the keyup event fired for the same key
* and keydown is not null
* Barcode never fired keydown event more than 1 time before the same key fired keyup event
* Barcode generally finishes all events (like keydown > keypress > keyup) of single key at a time, if two different keys are pressed then it is with keyboard
*/
if (cforKeyDown != (char) e.KeyCode || cforKeyDown == '\0')
{
cforKeyDown = '\0';
_barcode.Clear();
return;
}
// getting the time difference between 2 keys
int elapsed = (DateTime.Now.Millisecond - _lastKeystroke);
/*
* Barcode scanner usually takes less than 17 milliseconds to read, increase this if neccessary of your barcode scanner is slower
* also assuming human can not type faster than 17 milliseconds
*/
// Bumped it up to 35[ms]
if (elapsed > 50)
_barcode.Clear();
// Do not push in array if Enter/Return is pressed, since it is not any Character that need to be read
if (e.KeyCode != Keys.Return)
{
//_barcode.Add((char) e.KeyData);
_barcode.Add((char) e.KeyData);
}
// Barcode scanner hits Enter/Return after reading barcode
if (e.KeyCode == Keys.Return && _barcode.Count > 0)
{
string BarCodeData = new String(_barcode.ToArray());
if (!UseKeyboard)
{
//MessageBox.Show(String.Format("{0}", BarCodeData));
label1.Text = String.Format("{0}", BarCodeData);
}
//_barcode.Clear();
}
// update the last key stroke time
_lastKeystroke = DateTime.Now.Millisecond;
}
private void Form1_KeyDown(object sender, KeyEventArgs e)
{
//Debug.WriteLine("CS_Single_Label_Printer_KeyDown : " + (char)e.KeyCode);
cforKeyDown = (char) e.KeyCode;
}
I've narrowed down the problem to the fact that the alphabetic parts of the alpha-numeric barcodes being scanned are uppercase. I generated a test barcode using lower-case letters, and everything worked as it should, but this still doesn't fix the problem as I have to scan thousands of already printed barcodes that have uppercase characters encoded into the barcode data matrix.
Is there a way to switch the above code in order to account for the 'character | Shift' KeyData?

The answer is that KeyCode returns the KEY pressed. It does not respect the case of the key. Use Shift to get the case. Below is a working example based on your supplied code. The magic is in the local function ToCharacter. You'll need to play with the if statements at the top to include numbers too if that's your desire.
From1.cs
using System;
using System.Collections.Generic;
using System.Windows.Forms;
namespace DesktopApp2
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
char cforKeyDown = '\0';
int _lastKeystroke = DateTime.Now.Millisecond;
List<char> _barcode = new List<char>();
bool UseKeyboard = false;
private void Form1_Load(object sender, EventArgs e)
{
this.ActiveControl = InputBox;
this.InputBox.KeyDown += new KeyEventHandler(Form1_KeyDown);
this.InputBox.KeyUp += new KeyEventHandler(Form1_KeyUp);
}
private void Form1_KeyUp(object sender, KeyEventArgs e)
{
char NotALetter = '-';
DebugBox.Items.Clear();
DebugBox.Items.Add($"KeyEventArgs->KeyCode = {e.KeyCode.ToString()}");
DebugBox.Items.Add($"KeyEventArgs->KeyData = {e.KeyData.ToString()}");
DebugBox.Items.Add($"KeyEventArgs->KeyValue = {e.KeyValue.ToString()}");
DebugBox.Items.Add($"KeyEventArgs->e.Shift = {e.Shift.ToString()}");
DebugBox.Items.Add($"ToCharacter = {ToCharacter(e) ?? NotALetter}");
char? ToCharacter(KeyEventArgs kea)
{
int DtoNumPadOffset = (int)(Keys.NumPad0 - Keys.D0);
if (kea.KeyCode < Keys.D0) return null; // Keys.D0 through Kyes.D9 are the Keys on the top row of the keyboard. D9 is right next to A in the enum type.
if (kea.KeyCode > Keys.NumPad9) return null;
if (kea.KeyCode > Keys.Z && kea.KeyCode < Keys.NumPad0) return null; //knocks out keys between Z and NumPad0
if (kea.Shift && kea.KeyCode < Keys.A) return null; // rejects special characters when numbers across the top are used with the <shift> key.
if (kea.KeyCode < Keys.A) return (char)kea.KeyCode;
if (kea.KeyCode > Keys.Z) return (char)((int)kea.KeyCode - DtoNumPadOffset);
return kea.Shift
? (char)kea.KeyCode
: char.ToLower((char)kea.KeyCode);
}
// if keyboard input is allowed to read
if (UseKeyboard && e.KeyData != Keys.Enter)
{
MessageBox.Show(e.KeyData.ToString());
}
/* check if keydown and keyup is not different
* and keydown event is not fired again before the keyup event fired for the same key
* and keydown is not null
* Barcode never fired keydown event more than 1 time before the same key fired keyup event
* Barcode generally finishes all events (like keydown > keypress > keyup) of single key at a time, if two different keys are pressed then it is with keyboard
*/
//if (cforKeyDown != (char)e.KeyCode || cforKeyDown == '\0')
//{
// cforKeyDown = '\0';
// _barcode.Clear();
// return;
//}
// getting the time difference between 2 keys
int elapsed = (DateTime.Now.Millisecond - _lastKeystroke);
/*
* Barcode scanner usually takes less than 17 milliseconds to read, increase this if neccessary of your barcode scanner is slower
* also assuming human can not type faster than 17 milliseconds
*/
// Bumped it up to 35[ms]
//if (elapsed > 2000)
if (e.KeyCode == Keys.Return)
{
InputBox.Text = String.Empty;
_barcode.Clear();
}
// Do not push in array if Enter/Return is pressed, since it is not any Character that need to be read
if (e.KeyCode != Keys.Return)
{
char? TestForCharacter = ToCharacter(e);
if (TestForCharacter != null)
{
//_barcode.Add((char) e.KeyData);
_barcode.Add((char)TestForCharacter);
}
}
OutputBox.Text = string.Concat(_barcode);
// Barcode scanner hits Enter/Return after reading barcode
if (e.KeyCode == Keys.Return && _barcode.Count > 0)
{
string BarCodeData = new String(_barcode.ToArray());
if (!UseKeyboard)
{
//MessageBox.Show(String.Format("{0}", BarCodeData));
OutputBox.Text = String.Format("{0}", BarCodeData);
}
//_barcode.Clear();
}
// update the last key stroke time
_lastKeystroke = DateTime.Now.Millisecond;
}
private void Form1_KeyDown(object sender, KeyEventArgs e)
{
//Debug.WriteLine("CS_Single_Label_Printer_KeyDown : " + (char)e.KeyCode);
cforKeyDown = (char)e.KeyCode;
}
}
}
Form1.Designer.cs
namespace DesktopApp2
{
partial class Form1
{
/// <summary>
/// Required designer variable.
/// </summary>
private System.ComponentModel.IContainer components = null;
/// <summary>
/// Clean up any resources being used.
/// </summary>
/// <param name="disposing">true if managed resources should be disposed; otherwise, false.</param>
protected override void Dispose(bool disposing)
{
if (disposing && (components != null))
{
components.Dispose();
}
base.Dispose(disposing);
}
#region Windows Form Designer generated code
/// <summary>
/// Required method for Designer support - do not modify
/// the contents of this method with the code editor.
/// </summary>
private void InitializeComponent()
{
this.OutputBox = new System.Windows.Forms.TextBox();
this.InputBox = new System.Windows.Forms.TextBox();
this.DebugBox = new System.Windows.Forms.ListBox();
this.SuspendLayout();
//
// OutputBox
//
this.OutputBox.Location = new System.Drawing.Point(52, 93);
this.OutputBox.Name = "OutputBox";
this.OutputBox.ReadOnly = true;
this.OutputBox.Size = new System.Drawing.Size(650, 22);
this.OutputBox.TabIndex = 1;
//
// InputBox
//
this.InputBox.Location = new System.Drawing.Point(52, 45);
this.InputBox.Name = "InputBox";
this.InputBox.Size = new System.Drawing.Size(650, 22);
this.InputBox.TabIndex = 2;
//
// DebugBox
//
this.DebugBox.FormattingEnabled = true;
this.DebugBox.ItemHeight = 16;
this.DebugBox.Location = new System.Drawing.Point(52, 131);
this.DebugBox.Name = "DebugBox";
this.DebugBox.Size = new System.Drawing.Size(650, 308);
this.DebugBox.TabIndex = 3;
//
// Form1
//
this.AutoScaleDimensions = new System.Drawing.SizeF(8F, 16F);
this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
this.ClientSize = new System.Drawing.Size(716, 450);
this.Controls.Add(this.DebugBox);
this.Controls.Add(this.InputBox);
this.Controls.Add(this.OutputBox);
this.Name = "Form1";
this.Text = "Form1";
this.Load += new System.EventHandler(this.Form1_Load);
this.ResumeLayout(false);
this.PerformLayout();
}
#endregion
private System.Windows.Forms.TextBox OutputBox;
private System.Windows.Forms.TextBox InputBox;
private System.Windows.Forms.ListBox DebugBox;
}
}
Tidy helper class for dealing with KeyEventArgs
The Is* functions group the keycodes into ranges and detect (if appropriate) the shift states. To* functions produce the char that best represents the KeyCode in the event. ToAlphaNumericAsciiCharacter simply pairs up detectors with producers.
public static class KeyEventArgs_Functions
{
public static bool Between(this Keys source, Keys lhv, Keys rhv)
{
return source >= lhv && source <= rhv;
}
public static bool IsLetterKeyBoardChar(this KeyEventArgs source)
{
return source.KeyCode.Between(Keys.A, Keys.Z);
}
public static bool IsNumberKeyBoardChar(this KeyEventArgs source)
{
return !source.Shift && source.KeyCode.Between(Keys.D0, Keys.D9);
}
public static bool IsNumber10KeyPadChar(this KeyEventArgs source)
{
return source.KeyCode.Between(Keys.NumPad0, Keys.NumPad9);
}
public static char ToLetterKeyBoardChar(this KeyEventArgs source) // Only returns a valid value if IsLetterKeyBoardChar returns true.
{
return source.Shift ? (char)source.KeyCode: char.ToLower((char)source.KeyCode);
}
public static char ToNumberKeyBoardChar(this KeyEventArgs source) // Only returns a valid value if IsNumberKeyBoardChar returns true.
{
return (char)source.KeyCode;
}
public static char ToNumber10KeyPadChar(this KeyEventArgs source) // Only returns a valid value if IsNumber10KeyPadChar returns true.
{
const int DtoNumPadOffset = (int)(Keys.NumPad0 - Keys.D0);
return (char)((int)source.KeyCode - DtoNumPadOffset);
}
public static char? ToAlphaNumericAsciiCharacter(this KeyEventArgs source)
{
if (source.IsLetterKeyBoardChar()) return source.ToLetterKeyBoardChar();
if (source.IsNumberKeyBoardChar()) return source.ToNumberKeyBoardChar();
if (source.IsNumber10KeyPadChar()) return source.ToNumber10KeyPadChar();
return null;
}
}

How to register singular key press

I need to be able to press a key down and no matter how long it is held down for it only does the action once. I have tried using bools to keep track of the state but haven't had any luck.
bool downPressed = false;
int a = 0;
if (Keyboard.GetState().IsKeyDown(Keys.Down))
{
downPressed = true;
if (downPressed == true)
{
while(a == 0)
{
y += 100;
a++;
}
}
}
This is my latest attempt. The aim is for when the down key is pressed it moves the object by 100px but only once every time it is pressed.

You should add an EventHandler to your KeyDown Event of the Application/Form and just do the
y += 100;
in there.
public void OnKeyDown(object sender, System.Windows.Forms.KeyEventArgs e)
{
y += 100;
}

How to detect a custom key from Keyboard using C#

I have a USB Keyboard that have some Special keys like "FN",PLAY,MUTE and one that changes the keyboard light. I was trying to get what is this key "name" to perform a logic to change the color periodically.
private void textBox1_TextChanged(object sender, EventArgs e)
{
var key = sender as TextBox;
var result = key.Text;
}
But the key its not a string to be recognized. How can I do this ? Thanks!

I will suggest you to use OnKeyPress and OnKeyDown events instead to check what was pressed. MSDN Link.
Example:
// Boolean flag used to determine when a character other than a number is entered.
private bool nonNumberEntered = false;
// Handle the KeyDown event to determine the type of character entered into the control.
private void textBox1_KeyDown(object sender, System.Windows.Forms.KeyEventArgs e)
{
// Initialize the flag to false.
nonNumberEntered = false;
// Determine whether the keystroke is a number from the top of the keyboard.
if (e.KeyCode < Keys.D0 || e.KeyCode > Keys.D9)
{
// Determine whether the keystroke is a number from the keypad.
if (e.KeyCode < Keys.NumPad0 || e.KeyCode > Keys.NumPad9)
{
// Determine whether the keystroke is a backspace.
if(e.KeyCode != Keys.Back)
{
// A non-numerical keystroke was pressed.
// Set the flag to true and evaluate in KeyPress event.
nonNumberEntered = true;
}
}
}
//If shift key was pressed, it's not a number.
if (Control.ModifierKeys == Keys.Shift) {
nonNumberEntered = true;
}
}
// This event occurs after the KeyDown event and can be used to prevent
// characters from entering the control.
private void textBox1_KeyPress(object sender, System.Windows.Forms.KeyPressEventArgs e)
{
// Check for the flag being set in the KeyDown event.
if (nonNumberEntered == true)
{
// Stop the character from being entered into the control since it is non-numerical.
e.Handled = true;
}
}

How do I make ASWD keyboard movement control

I have started to learn some Microsoft.DirectX 3D basic techniques, and bumped to this problem that is too dificult for me. I have created 3D Scene, Camera, Light's etc, with some simple 3D objects drawn. What I want to do now is simple 3D rotation of that objects around all three axes. For that I want to use Arrow and ASWD keyboard keys as in manner in computer games are used. For that I have used OnKeyDown and OnKeyUp event handlers :
#region - Event handler -
protected override void OnKeyDown(KeyEventArgs e)
{
base.OnKeyDown(e);
#region - speed -
if(e.KeyValue == (char)Keys.Add || e.KeyValue == (char)Keys.Oemplus)
step_p = true;
if(e.KeyValue == (char)Keys.Subtract || e.KeyValue == (char)Keys.OemMinus)
step_m = true;
if(step_p)
step++;
if(step_m)
step--;
if(step==0)
step = 1;
#endregion
#region - rotation -
if(e.KeyCode == Keys.Left)
{
left = true;
}
if(e.KeyCode == Keys.Right)
{
right = true;
}
if(e.KeyCode == Keys.Up)
{
up = true;
}
if(e.KeyCode == Keys.Down)
{
down = true;
}
if(e.KeyCode == Keys.A)
{
a = true;
}
if(e.KeyCode == Keys.D)
{
d = true;
}
if(left)
angleZ_D+=step;
if(right)
angleZ_D-=step;
if(up)
angleX_D-=step;
if(down)
angleX_D+=step;
if(a)
angleY_D+=step;
if(d)
angleY_D-=step;
//
//
//
if(angleX_D == 360)
angleX_D = 0;
if(angleY_D >= 360)
angleY_D = 0;
if(angleZ_D >= 360)
angleZ_D = 0;
angleX_R = angleX_D * rad;
angleY_R = angleY_D * rad;
angleZ_R = angleZ_D * rad;
//
//
//
#endregion
#region - zoom -
if(e.KeyValue == (char)Keys.W)
{
w = true;
}
if(e.KeyValue == (char)Keys.S)
{
s = true;
}
if(w)
{
zoom+=0.1f * step;
if(zoom>10.0f) zoom=10.0f;
}
if(s)
{
zoom-=0.1f * step;
if(zoom<1.0f) zoom=1.0f;
}
#endregion
Draw();
}
protected override void OnKeyUp(KeyEventArgs e)
{
base.OnKeyUp(e);
#region - speed -
if(e.KeyValue == (char)Keys.Add || e.KeyValue == (char)Keys.Oemplus)
step_p = false;
if(e.KeyValue == (char)Keys.Subtract || e.KeyValue == (char)Keys.OemMinus)
step_m = false;
#endregion
#region - rotation -
if(e.KeyCode == Keys.Left)
{
left = false;
}
if(e.KeyCode == Keys.Right)
{
right = false;
}
if(e.KeyCode == Keys.Up)
{
up = false;
}
if(e.KeyCode == Keys.Down)
{
down = false;
}
if(e.KeyCode == Keys.A)
{
a = false;
}
if(e.KeyCode == Keys.D)
{
d = false;
}
#endregion
#region - zoom -
if(e.KeyValue == (char)Keys.W)
{
w = false;
}
if(e.KeyValue == (char)Keys.S)
{
s = false;
}
#endregion
Draw();
}
This is the problem :
When I press key A and while holding it down I press key W, program works perfectly but when I release key W the event handler do not recognize that key A is still pressed.
Is there solution for such problem in C# 4.0 and .Net framework 2.0
All the best,
Željko Perić
According to
Quote:
You are depending on the keyboard repeating a key when held down.
That stops working as soon as you press another key.
You instead need to use a Timer and in the Tick event handler
check which way you want to move. Now key-repeat no longer matters.
Set the timer's Interval property to 15 or 31 to get good consistency. – Hans Passant
this is problem solution :
using System;
using System.Windows.Forms;
namespace WASD_keyboard_game_control
{
public partial class MainForm : Form
{
//
// Global variables declaration
//
//
// Timer
//
// Implements a timer that
// raises event at user defined interval
//
Timer Clock;
//
// Set Timer tick Interval in miliseconds
//
// By changing value of Interval,
// we control how often the timer tick event handler is raised
// and eventually the call frequency of Main_Function()
//
const int Interval = 15;
//
// Variables for counting the number
// of times that program has confirmed
// the key down state of AWSD keys
//
int W = 0;
int A = 0;
int S = 0;
int D = 0;
//
// Variables ( flags ) for memorizing
// the key down state of AWSD keys
//
// true - key is down ( pressed )
//
// false - key is up ( released )
//
//
bool w = false;
bool a = false;
bool s = false;
bool d = false;
//
//
//
public MainForm()
{
//
// The InitializeComponent() call is required
// for Windows Forms designer support.
//
InitializeComponent();
//
// Call Initialize_Timer() function
//
Initialize_Timer();
}
void Initialize_Timer()
{
// Create new timer
Clock = new Timer();
// Set timer tick interval in miliseconds
//
// By changing value of interval,
// we control how often the timer tick event handler is raised
// and eventually the call frequency of Main_Function()
//
Clock.Interval = Interval;
//
// Add timer tick event handler
//
// This event handler is raised
// every time timer make tick
//
// The smaler value for timer interval,
// more often the event handler is raised
//
Clock.Tick += new System.EventHandler(this.ClockTick);
//
// Start timer
//
Clock.Start();
}
void ClockTick(object sender, EventArgs e)
{
//
// Timer tick event handler
//
//
// Call Main_Function()
//
Main_Function();
//
//
//
}
protected override void OnKeyDown(KeyEventArgs e)
{
//
// This event handler is raised every time
// some key on the keyboard is first pressed
//
base.OnKeyDown(e);
//
// Set corresponding key down flag state to true
//
if(e.KeyCode == Keys.W)
w = true;
if(e.KeyCode == Keys.A)
a = true;
if(e.KeyCode == Keys.S)
s = true;
if(e.KeyCode == Keys.D)
d = true;
}
protected override void OnKeyUp(KeyEventArgs e)
{
//
// This event handler is raised every time
// some key on the keyboard is released
//
base.OnKeyUp(e);
//
// Set corresponding key down flag state to false
//
if(e.KeyCode == Keys.W)
w = false;
if(e.KeyCode == Keys.A)
a = false;
if(e.KeyCode == Keys.S)
s = false;
if(e.KeyCode == Keys.D)
d = false;
}
void Main_Function()
{
//
// Main function
//
//
// This function is called every time the
// timer tick event handler is raised
//
//
// This function determines wich key is pressed
// upon key down flag value and updates correspondig counter value
//
// Counter value shows how many times program has confirmed the
// key down state and not how many times user has pressed the key
//
//
// Increase counter value if key is down
//
if(a)
A++;
if(s)
S++;
if(w)
W++;
if(d)
D++;
//
// Show values of counters
//
Label_A.Text = "A = " + A.ToString();
Label_S.Text = "S = " + S.ToString();
Label_W.Text = "W = " + W.ToString();
Label_D.Text = "D = " + D.ToString();
}
}
}

How do I prevent the up and down keys from moving the caret/cursor in a textbox to the left and right in a c# windows form.

I'm currently trying to increase the index of the cursor by 1. For example, if my blinking cursor was between 2 and 1 in 210, it would increase the value to 220.
This is part of the code I'm using right now. I'm trying to get the cursor to stay in its place after pressing down, and its moving to the right. I tried to set the SelectionStart back to 0 but the box increases it by 1 by default (my textbox's first caret index starts on the very left).
TextBox textBox = (TextBox)sender;
int box_int = 0;
Int32.TryParse(textBox.Text, out box_int);
if (e.KeyCode == Keys.Down)
{
if(textBox.SelectionStart == 0)
{
box_int -= 10000;
textBox.Text = box_int.ToString();
textBox.SelectionStart= 0;
return;
}
}

In order to prevent the caret (not the cursor) from moving, you should set e.Handled = true; in your event handler. This code changes the digit to the right of the caret when the up or down arrow is pressed. If the up or down arrow is pressed, the e.Handled is set to true to prevent the movement of the caret. This code is not fully tested, but seems to work. I also set the textbox ReadOnly property to true and preset the value to "0".
private void textBox1_KeyDown(object sender, KeyEventArgs e)
{
TextBox textBox = (TextBox)sender;
//Only change the digit if there is no selection
if (textBox.SelectionLength == 0)
{
//Save the current caret position to restore it later
int selStart = textBox.SelectionStart;
//These next few lines determines how much to add or subtract
//from the value based on the caret position in the number.
int box_int = 0;
Int32.TryParse(textBox.Text, out box_int);
int powerOf10 = textBox.Text.Length - textBox.SelectionStart - 1;
//If the number is negative, the SelectionStart will be off by one
if (box_int < 0)
{
powerOf10++;
}
//Calculate the amount to change the textbox value by.
int valueChange = (int)Math.Pow(10.0, (double)powerOf10);
if (e.KeyCode == Keys.Down)
{
box_int -= valueChange;
e.Handled = true;
}
if (e.KeyCode == Keys.Up)
{
box_int += valueChange;
e.Handled = true;
}
textBox.Text = box_int.ToString();
textBox.SelectionStart = selStart;
}
}