C#下usb条码扫描枪的钩子实现的改进

  【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。】

frmMain:

        public BarCodeHook BarCode = new BarCodeHook();        public delegate void ShowInfoDelegate(BarCodeHook.BarCodes barCode);        void ShowInfo(BarCodeHook.BarCodes barCode){         textBox_barCode.Text = barCode.BarCode;         buttonX2.Focus();        }        public void BarCode_BarCodeEvent(BarCodeHook.BarCodes barCode)        {            ShowInfo(barCode);        }        public frmMain()        {            InitializeComponent();            BarCode.BarCodeEvent += new BarCodeHook.BarCodeDelegate(BarCode_BarCodeEvent);        }

如果焦点本来就在textBox上，会产生多余的字符，所以在showInfo函数里，每次都手动让buttonX2成为焦点。

 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;        public string strBarCode = "";        public int length;        private int KeyboardHookProc(int nCode, Int32 wParam, IntPtr lParam)        {            barCode.IsValid = false;            bool notChar = false;            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);                    }                    else                    {                        notChar = true;   //转到ascii字符失败，这不是一个正常字符，要去掉                    }                            if (DateTime.Now.Subtract(barCode.Time).TotalMilliseconds > 30)     //30ms可以过滤掉连续按住一个键时的情况                            {                                if (notChar == false)                                    strBarCode = barCode.Chr.ToString();                                else                                    strBarCode = "";                                barCode.IsValid = false;                            }                            else                            {                                if (strBarCode.Length >= 5)                                  {                                    barCode.IsValid = true;      //isValid为true表明这是个条码                                }                                if (notChar == false)                                {                                    strBarCode += barCode.Chr.ToString();                                }                                barCode.BarCode = strBarCode;                            }                                        barCode.Time = DateTime.Now;                    if (BarCodeEvent != null && barCode.IsValid) BarCodeEvent(barCode);    //触发事件                                    }            }            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)            {                bool result = UnhookWindowsHookEx(hKeyboardHook);                hKeyboardHook = 0;         //将hKeyboardHook 置为0                if (result)                {                    //MessageBox.Show("true");                }                return result;            }                        return true;        }    }

是如果扫到的是英文字符的话，会有一个多余的码无法从键盘码转到ascii码，需要去掉这个码。同时设为30ms可以过滤掉一直按住一个键的情况。