3年前写了一篇《USB口的红外条形码扫描器的另类使用》，不过相关代码是VB编写，在这几年之间，有许多网友提出需要C#版的，起初还以为由VB修改C#应该很容易，最近研究了一下，发现C#和VB调用API的机制还是有所不同的，在迁移的过程中还是会遇到不少问题，所以我专门抽时间做了一个基于C#的程序。

      【目前的条形码扫描器有点类似外接键盘（其实从消息传送上它就相当于一个键盘），把输入焦点定位到可输入的控件上，一扫描相应的条形码信息就输入到文本框中去了，但是如果没有输入焦点，或另一个不相干的程序获得输入焦点，那就有点乱套了。我想实现的是，不管什么情况，只要扫描器一工作，我的程序就能自动激活，并能获得当前输入的条形码信息。 实现思路：我用的是litele牌的USB口的红外条形码扫描器，仔细分析了一下，扫描成功后，以键盘按键消息的形式把条形码输入信息通知给系统。这样通过键盘钩子就可以方便的获得该信息了。但是，怎样区分信息是键盘还是条形码输入的哪？很简单，条形码扫描器在很短的时间内输入了至少3个字符以上信息，并且以“回车”作为结束字符，在这种思想指引下，很完美的实现了预定功能。】

     VB相关的代码请见：http://blog.csdn.net/yefanqiu/archive/2006/08/30/1144881.aspx

窗体相关代码：

 using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;

namespace ReadBadCode
{
    public partial class frmTest : Form
    {
        BarCodeHook BarCode = new BarCodeHook();
        public frmTest()
        {
            InitializeComponent();
            BarCode.BarCodeEvent += new BarCodeHook.BarCodeDelegate(BarCode_BarCodeEvent);
        }

        private delegate void ShowInfoDelegate(BarCodeHook.BarCodes barCode);
        private void ShowInfo(BarCodeHook.BarCodes barCode)
        {
            if (this.InvokeRequired)
            {
                this.BeginInvoke(new ShowInfoDelegate(ShowInfo), new object[] { barCode });
            }
            else
            {
                textBox1.Text = barCode.KeyName;
                textBox2.Text = barCode.VirtKey.ToString();
                textBox3.Text = barCode.ScanCode.ToString();
                textBox4.Text = barCode.AscII.ToString();
                textBox5.Text = barCode.Chr.ToString();
                textBox6.Text = barCode.IsValid ? barCode.BarCode : "";
            }
        }

        void BarCode_BarCodeEvent(BarCodeHook.BarCodes barCode)
        {
            ShowInfo(barCode);
        }

        private void frmTest_Load(object sender, EventArgs e)
        {
            BarCode.Start();
        }

        private void frmTest_FormClosed(object sender, FormClosedEventArgs e)
        {
            BarCode.Stop();
        }

        private void textBox6_TextChanged(object sender, EventArgs e)
        {
            if (textBox6.Text.Length > 0)
            {
                MessageBox.Show(textBox6.Text);
            }
        }
    }
}

BarCodeHook 类：

using System;
using System.Collections.Generic;
using System.Text;
using System.Runtime.InteropServices;
using System.Reflection;

namespace ReadBadCode
{
    public class BarCodeHook
    {
        public delegate void BarCodeDelegate(BarCodes barCode);
        public event BarCodeDelegate BarCodeEvent;

        public struct BarCodes
        {
            public int VirtKey;      //虚拟码
            public int ScanCode;     //扫描码
            public string KeyName;   //键名
            public uint AscII;       //AscII
            public char Chr;         //字符

            public string BarCode;   //条码信息
            public bool IsValid;     //条码是否有效
            public DateTime Time;    //扫描时间
        }

        private struct EventMsg
        {
            public int message;
            public int paramL;
            public int paramH;
            public int Time;
            public int hwnd;
        }
       
        [DllImport("user32.dll", CharSet = CharSet.Auto, CallingConvention = CallingConvention.StdCall)]
        private static extern int SetWindowsHookEx(int idHook, HookProc lpfn, IntPtr hInstance, int threadId);

        [DllImport("user32.dll", CharSet = CharSet.Auto, CallingConvention = CallingConvention.StdCall)]
        private static extern bool UnhookWindowsHookEx(int idHook);

        [DllImport("user32.dll", CharSet = CharSet.Auto, CallingConvention = CallingConvention.StdCall)]
        private static extern int CallNextHookEx(int idHook, int nCode, Int32 wParam, IntPtr lParam);

        [DllImport("user32", EntryPoint = "GetKeyNameText")]
        private static extern int GetKeyNameText(int lParam, StringBuilder lpBuffer, int nSize);

        [DllImport("user32", EntryPoint = "GetKeyboardState")]
        private static extern int GetKeyboardState(byte[] pbKeyState);

        [DllImport("user32", EntryPoint = "ToAscii")]
        private static extern bool ToAscii(int VirtualKey, int ScanCode, byte[] lpKeyState, ref uint lpChar, int uFlags);

        delegate int HookProc(int nCode, Int32 wParam, IntPtr lParam);
        BarCodes barCode = new BarCodes();
        int hKeyboardHook = 0;
        string strBarCode = "";

        private int KeyboardHookProc(int nCode, Int32 wParam, IntPtr lParam)
        {
            if (nCode == 0)
            {
                EventMsg msg = (EventMsg)Marshal.PtrToStructure(lParam, typeof(EventMsg));

                if (wParam == 0x100)   //WM_KEYDOWN = 0x100
                {
                    barCode.VirtKey = msg.message & 0xff;  //虚拟码
                    barCode.ScanCode = msg.paramL & 0xff;  //扫描码

                    StringBuilder strKeyName = new StringBuilder(255);
                    if (GetKeyNameText(barCode.ScanCode * 65536, strKeyName, 255) > 0)
                    {
                        barCode.KeyName = strKeyName.ToString().Trim(new char[] { ' ', '/0' });
                    }
                    else
                    {
                        barCode.KeyName = "";
                    }

                    byte[] kbArray = new byte[256];
                    uint uKey = 0;
                    GetKeyboardState(kbArray);                                        
                    if (ToAscii(barCode.VirtKey, barCode.ScanCode, kbArray, ref uKey, 0))
                    {
                        barCode.AscII = uKey;
                        barCode.Chr = Convert.ToChar(uKey);
                    }

                    if (DateTime.Now.Subtract(barCode.Time).TotalMilliseconds > 50) 
                    {
                        strBarCode = barCode.Chr.ToString();
                    }
                    else
                    {
                        if ((msg.message & 0xff) == 13 && strBarCode.Length > 3)   //回车
                        {
                            barCode.BarCode = strBarCode;
                            barCode.IsValid = true;
                        }
                        strBarCode += barCode.Chr.ToString();
                    }

                    barCode.Time = DateTime.Now;
                    if (BarCodeEvent != null) BarCodeEvent(barCode);    //触发事件
                    barCode.IsValid = false;
                }
            }
            return CallNextHookEx(hKeyboardHook, nCode, wParam, lParam);          
        }
        
        // 安装钩子 
        public bool Start()
        {
            if (hKeyboardHook == 0)
            {
                //WH_KEYBOARD_LL = 13
                hKeyboardHook = SetWindowsHookEx(13, new HookProc(KeyboardHookProc), Marshal.GetHINSTANCE(Assembly.GetExecutingAssembly().GetModules()[0]), 0);
            }
            return (hKeyboardHook != 0);
        }

        // 卸载钩子 
        public bool Stop()
        {
            if (hKeyboardHook != 0)
            {
                return UnhookWindowsHookEx(hKeyboardHook);
            }
            return true;
        }
    }
}

 【注意】和VB程序不同，要想测试实际的效果，必须执行编译后的Exe文件，在开发环境直接运行会没有效果的