C#USB扫码枪实现无焦点状态下扫入

以下内容是复制这个大神的文章，解决了USB扫码枪无焦点扫码的问题，非常感谢，我留个笔记

https://www.cnblogs.com/TBW-Superhero/p/8659306.html

1.扫描枪获取数据原理基本相当于键盘数据，获取扫描枪扫描出来的数据，一般分为两种实现方式。

a）文本框输入获取焦点，扫描后自动显示在文本框内。

b）使用键盘钩子，勾取扫描枪虚拟按键，根据按键频率进行手动输入和扫描枪扫描判断。

2.要实现系统钩子其实很简单，调用三个Win32的API即可。

SetWindowsHookEx 用于设置钩子。（设立一道卡子，盘查需要的信息）

CallNextHookEx 用于传递钩子（消息是重要的，所以从哪里来，就应该回到哪里去，除非你决定要封锁消息）

UnhookWindowsHookEx 卸载钩子（卸载很重要，卡子设多了会造成拥堵）

3，代码实现

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Diagnostics;
using System.Runtime.InteropServices;


namespace Helper
{
    public class BarcodeScannerHelper
    {
        //public delegate void ScanerDelegate(ScanerCodes codes);
        public delegate void ScanerDelegate(string codes);
        public event ScanerDelegate ScanerEvent;

        //private const int WM_KEYDOWN = 0x100;//KEYDOWN
        //private const int WM_KEYUP = 0x101;//KEYUP
        //private const int WM_SYSKEYDOWN = 0x104;//SYSKEYDOWN
        //private const int WM_SYSKEYUP = 0x105;//SYSKEYUP
        //private static int HookProc(int nCode, Int32 wParam, IntPtr lParam);

        /// <summary>
        /// 声明键盘钩子处理的初始值
        /// </summary>
        private int hKeyboardHook = 0;
        private ScanerCodes codes = new ScanerCodes();//13为键盘钩子

        //定义成静态，这样不会抛出回收异常
        private static HookProc hookproc;
        delegate int HookProc(int nCode, Int32 wParam, IntPtr lParam);
        [DllImport("user32.dll", CharSet = CharSet.Auto, CallingConvention = CallingConvention.StdCall)]
        //设置钩子（设立一道卡子，盘查需要的信息）
        private static extern int SetWindowsHookEx(int idHook, HookProc lpfn, IntPtr hInstance, int threadId);
        [DllImport("user32.dll", CharSet = CharSet.Auto, CallingConvention = CallingConvention.StdCall)]
        //卸载钩子 （卸载很重要，卡子设多了会造成拥堵）
        private static extern bool UnhookWindowsHookEx(int idHook);
        [DllImport("user32.dll", CharSet = CharSet.Auto, CallingConvention = CallingConvention.StdCall)]
        //继续下个钩子 用于传递钩子（消息是重要的，所以从哪里来，就应该回到哪里去，除非你决定要封锁消息）
        private static extern int CallNextHookEx(int idHook, int nCode, Int32 wParam, IntPtr lParam);

        [DllImport("user32", EntryPoint = "GetKeyNameText")]
        private static extern int GetKeyNameText(int IParam, StringBuilder lpBuffer, int nSize);
        [DllImport("user32", EntryPoint = "GetKeyboardState")]
        //获取按键的状态
        private static extern int GetKeyboardState(byte[] pbKeyState);
        [DllImport("user32", EntryPoint = "ToAscii")]
        //ToAscii职能的转换指定的虚拟键码和键盘状态的相应字符或字符
        private static extern bool ToAscii(int VirtualKey, int ScanCode, byte[] lpKeySate, ref uint lpChar, int uFlags);

        //int VirtualKey //[in] 指定虚拟关键代码进行翻译。
        //int uScanCode, // [in] 指定的硬件扫描码的关键须翻译成英文。高阶位的这个值设定的关键，如果是（不压）
        //byte[] lpbKeyState, // [in] 指针，以256字节数组，包含当前键盘的状态。每个元素（字节）的数组包含状态的一个关键。如果高阶位的字节是一套，关键是下跌（按下）。在低比特，如/果设置表明，关键是对切换。在此功能，只有肘位的CAPS LOCK键是相关的。在切换状态的NUM个锁和滚动锁定键被忽略。
        //byte[] lpwTransKey, // [out] 指针的缓冲区收到翻译字符或字符。
        //uint fuState); // [in] Specifies whether a menu is active. This parameter must be 1 if a menu is active, or 0 otherwise.



        [DllImport("kernel32.dll")]
        //使用WINDOWS API函数代替获取当前实例的函数,防止钩子失效
        public static extern IntPtr GetModuleHandle(string name);
        public BarcodeScannerHelper()
        {
        }
        public bool Start()
        {
            if (hKeyboardHook == 0)
            {
                hookproc = new HookProc(KeyboardHookProc);
                //GetModuleHandle 函数 替代 Marshal.GetHINSTANCE  
                //防止在 framework4.0中 注册钩子不成功  
                IntPtr modulePtr = GetModuleHandle(Process.GetCurrentProcess().MainModule.ModuleName);
                //WH_KEYBOARD_LL=13  
                //全局钩子 WH_KEYBOARD_LL  
                //  hKeyboardHook = SetWindowsHookEx(13, hookproc, Marshal.GetHINSTANCE(Assembly.GetExecutingAssembly().GetModules()[0]), 0);  
                hKeyboardHook = SetWindowsHookEx(13, hookproc, modulePtr, 0);
            }
            return (hKeyboardHook != 0);
        }


        public bool Stop()
        {
            if (hKeyboardHook != 0)
            {
                bool retKeyboard = UnhookWindowsHookEx(hKeyboardHook);
                hKeyboardHook = 0;
                return retKeyboard;
            }
            return true;
        }

        private int KeyboardHookProc(int nCode, Int32 wParam, IntPtr lParam)
        {
            EventMsg msg = (EventMsg)Marshal.PtrToStructure(lParam, typeof(EventMsg));
            codes.Add(msg);
            if (ScanerEvent != null && msg.message == 13 && msg.paramH > 0 && !string.IsNullOrEmpty(codes.Result))
            {
                //ScanerEvent(codes);
                ScanerEvent(codes.Result);
            }
            return CallNextHookEx(hKeyboardHook, nCode, wParam, lParam);
        }
        public class ScanerCodes
        {
            private int ts = 100; // 指定输入间隔为300毫秒以内时为连续输入  
            private List<List<EventMsg>> _keys = new List<List<EventMsg>>();
            private List<int> _keydown = new List<int>();   // 保存组合键状态  
            private List<string> _result = new List<string>();  // 返回结果集  
            private DateTime _last = DateTime.Now;
            private byte[] _state = new byte[256];
            private string _key = string.Empty;
            private string _cur = string.Empty;
            public EventMsg Event
            {
                get
                {
                    if (_keys.Count == 0)
                    {
                        return new EventMsg();
                    }
                    else
                    {
                        return _keys[_keys.Count - 1][_keys[_keys.Count - 1].Count - 1];
                    }
                }
            }
            public List<int> KeyDowns
            {
                get
                {
                    return _keydown;
                }
            }
            public DateTime LastInput
            {
                get
                {
                    return _last;
                }
            }
            public byte[] KeyboardState
            {
                get
                {
                    return _state;
                }
            }
            public int KeyDownCount
            {
                get
                {
                    return _keydown.Count;
                }
            }
            public string Result
            {
                get
                {
                    if (_result.Count > 0)
                    {
                        return _result[_result.Count - 1].Trim();
                    }
                    else
                    {
                        return null;
                    }
                }
            }
            public string CurrentKey
            {
                get
                {
                    return _key;
                }
            }
            public string CurrentChar
            {
                get
                {
                    return _cur;
                }
            }
            public bool isShift
            {
                get
                {
                    return _keydown.Contains(160);
                }
            }
            public void Add(EventMsg msg)
            {
                #region 记录按键信息           

                // 首次按下按键  
                if (_keys.Count == 0)
                {
                    _keys.Add(new List<EventMsg>());
                    _keys[0].Add(msg);
                    _result.Add(string.Empty);
                }
                // 未释放其他按键时按下按键  
                else if (_keydown.Count > 0)
                {
                    _keys[_keys.Count - 1].Add(msg);
                }
                // 单位时间内按下按键  
                else if (((TimeSpan)(DateTime.Now - _last)).TotalMilliseconds < ts)
                {
                    _keys[_keys.Count - 1].Add(msg);
                }
                // 从新记录输入内容  
                else
                {
                    _keys.Add(new List<EventMsg>());
                    _keys[_keys.Count - 1].Add(msg);
                    _result.Add(string.Empty);
                }
                #endregion
                _last = DateTime.Now;
                #region 获取键盘状态
                // 记录正在按下的按键  
                if (msg.paramH == 0 && !_keydown.Contains(msg.message))
                {
                    _keydown.Add(msg.message);
                }
                // 清除已松开的按键  
                if (msg.paramH > 0 && _keydown.Contains(msg.message))
                {
                    _keydown.Remove(msg.message);
                }
                #endregion
                #region 计算按键信息

                int v = msg.message & 0xff;
                int c = msg.paramL & 0xff;
                StringBuilder strKeyName = new StringBuilder(500);
                if (GetKeyNameText(c * 65536, strKeyName, 255) > 0)
                {
                    _key = strKeyName.ToString().Trim(new char[] { ' ', '\0' });
                    GetKeyboardState(_state);
                    if (_key.Length == 1 && msg.paramH == 0)// && msg.paramH == 0
                    {
                        // 根据键盘状态和shift缓存判断输出字符  
                        _cur = ShiftChar(_key, isShift, _state).ToString();
                        _result[_result.Count - 1] += _cur;
                    }
                    // 备选
                    //判断是+ 强制添加+
                    else if (_key.Length == 5 && msg.paramH == 0 && msg.paramL == 78 && msg.message == 107)// && msg.paramH == 0
                    {
                        // 根据键盘状态和shift缓存判断输出字符  
                        _cur = Convert.ToChar('+').ToString();
                        _result[_result.Count - 1] += _cur;
                    }

                    else
                    {
                        _cur = string.Empty;
                    }
                }
                #endregion
            }
            private char ShiftChar(string k, bool isShiftDown, byte[] state)
            {
                bool capslock = state[0x14] == 1;
                bool numlock = state[0x90] == 1;
                bool scrolllock = state[0x91] == 1;
                bool shiftdown = state[0xa0] == 1;
                char chr = (capslock ? k.ToUpper() : k.ToLower()).ToCharArray()[0];
                if (isShiftDown)
                {
                    if (chr >= 'a' && chr <= 'z')
                    {
                        chr = (char)((int)chr - 32);
                    }
                    else if (chr >= 'A' && chr <= 'Z')
                    {
                        if (chr == 'Z')
                        {
                            string s = "";
                        }
                        chr = (char)((int)chr + 32);
                    }
                    else
                    {
                        string s = "`1234567890-=[];',./";
                        string u = "~!@#$%^&*()_+{}:\"<>?";
                        if (s.IndexOf(chr) >= 0)
                        {
                            return (u.ToCharArray())[s.IndexOf(chr)];
                        }
                    }
                }
                return chr;
            }
        }
        public struct EventMsg
        {
            public int message;
            public int paramL;
            public int paramH;
            public int Time;
            public int hwnd;
        }
    }
}

　　

4，在项目中使用

namespace Test
{
    public partial class Form1 : Form
    {
        Helper.BarcodeScannerHelper scannerListener=new BarcodeScannerHelper();
        public Form1()
        {
            scannerListener.ScanerEvent += ScannerListener_ScanerEvent;
        }

        private void ScannerListener_ScanerEvent(string codes)
        {
            this.ricScanContent2.AppendText(codes+"\n");
        }


        private void Form1_Load(object sender, EventArgs e)
        {
            this.scannerListener.Start();
        }

        private void Form1_FormClosing(object sender, FormClosingEventArgs e)
        { 
 
            this.scannerListener.Stop();
        }
    }
}