【目前的條形碼掃描器有點類似外接鍵盤（其實從訊息傳送上它就相當於一個鍵盤），把輸入焦點定位到可輸入的控制元件上，一掃描相應的條形碼資訊就輸入到文字框中去了，但是如果沒有輸入焦點，或另一個不相干的程式獲得輸入焦點，那就有點亂套了。我想實現的是，不管什麼情況，只要掃描器一工作，我的程式就能自動啟用，並能獲得當前輸入的條形碼資訊。 實現思路：我用的是litele牌的USB口的紅外條形碼掃描器，仔細分析了一下，掃描成功後，以鍵盤按鍵訊息的形式把條形碼輸入資訊通知給系統。這樣通過鍵盤鉤子就可以方便的獲得該資訊了。但是，怎樣區分資訊是鍵盤還是條形碼輸入的哪？很簡單，條形碼掃描器在很短的時間內輸入了至少3個字元以上資訊，並且以“回車”作為結束字元，在這種思想指引下，很完美的實現了預定功能。】

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);

        }
 

如果焦點本來就在textBox上，會產生多餘的字元，所以在showInfo函式裡，每次都手動讓buttonX2成為焦點。

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

        public struct BarCodes
        {
            public int VirtKey;      //虛擬碼
            public int ScanCode;     //掃描碼
            public string KeyName;   //鍵名
            public uint AscII;       //AscII
            public char Chr;         //字元

            public string BarCode;   //條碼資訊
            public bool IsValid;     //條碼是否有效
            public DateTime Time;    //掃描時間
        }

        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;  //虛擬碼
                    barCode.ScanCode = msg.paramL & 0xff;  //掃描碼

                    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;   //轉到ascii字元失敗，這不是一個正常字元，要去掉
                    }


                            if (DateTime.Now.Subtract(barCode.Time).TotalMilliseconds > 30)     //30ms可以過濾掉連續按住一個鍵時的情況
                            {
                                if (notChar == false)
                                    strBarCode = barCode.Chr.ToString();
                                else
                                    strBarCode = "";
                                barCode.IsValid = false;
                            }
                            else
                            {
                                if (strBarCode.Length >= 5)  
                                {
                                    barCode.IsValid = true;      //isValid為true表明這是個條碼
                                }
                                if (notChar == false)
                                {
                                    strBarCode += barCode.Chr.ToString();
                                }
                                barCode.BarCode = strBarCode;
                            }


                    


                    barCode.Time = DateTime.Now;
                    if (BarCodeEvent != null && barCode.IsValid) BarCodeEvent(barCode);    //觸發事件
                    
                }
            }
            return CallNextHookEx(hKeyboardHook, nCode, wParam, lParam);          
        }
        
        // 安裝鉤子 
        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);
        }

        // 解除安裝鉤子 
        public bool Stop()
        {
            if (hKeyboardHook != 0)
            {
                bool result = UnhookWindowsHookEx(hKeyboardHook);
                hKeyboardHook = 0;         //將hKeyboardHook 置為0
                if (result)
                {

                    //MessageBox.Show("true");
                }
                return result;
            }
            
            return true;
        }
    }
 

是如果掃到的是英文字元的話，會有一個多餘的碼無法從鍵盤碼轉到ascii碼，需要去掉這個碼。同時設為30ms可以過濾掉一直按住一個鍵的情況。