//使用方法，脚本挂在场景中物体上即可
using System;
using System.Collections;
using System.Collections.Generic;
using System.Diagnostics;
using System.Runtime.InteropServices;
//using System.Windows.Forms;
using UnityEngine;

public class InterceptKeys : MonoBehaviour
{
    //安装钩子
    [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
    private static extern IntPtr SetWindowsHookEx(int idHook, LowLevelKeyboardProc lpfn, IntPtr hMod, uint dwThreadId);


    //卸载钩子
    [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
    [return: MarshalAs(UnmanagedType.Bool)]
    private static extern bool UnhookWindowsHookEx(IntPtr hhk);

    //向下传递钩子
    [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
    private static extern IntPtr CallNextHookEx(IntPtr hhk, int nCode, IntPtr wParam, IntPtr lParam);

    //获取程序集模块的句柄
    [DllImport("kernel32.dll", CharSet = CharSet.Auto, SetLastError = true)]
    private static extern IntPtr GetModuleHandle(string lpModuleName);

    //全局钩子键盘为13
    private const int WH_KEYBOARD_LL = 13;

    //按下键
    private const int WM_KEYDOWN = 0x0100;

    private static LowLevelKeyboardProc _proc = HookCallback;

    private static IntPtr _hookID = IntPtr.Zero;

    void Start()
    {
        _hookID = SetHook(_proc);
    }


    void OnApplicationQuit()
    {
        UnhookWindowsHookEx(_hookID);
    }

    //安装Hook,用于截获键盘。
    private static IntPtr SetHook(LowLevelKeyboardProc proc)
    {
        using (Process curProcess = Process.GetCurrentProcess())
        using (ProcessModule curModule = curProcess.MainModule)
        {
            return SetWindowsHookEx(WH_KEYBOARD_LL, proc, GetModuleHandle(curModule.ModuleName), 0);
        }
    }

    private delegate IntPtr LowLevelKeyboardProc(int nCode, IntPtr wParam, IntPtr lParam);

    private static IntPtr HookCallback(int nCode, IntPtr wParam, IntPtr lParam)
    {
        //nCode>0表示此消息已由Hook函数处理了,不会交给Windows窗口过程处理了
        //nCode=0则表示消息继续传递给Window消息处理函数
        if (nCode >= 0 && wParam == (IntPtr)WM_KEYDOWN)
        {
            int vkCode = Marshal.ReadInt32(lParam);
            //UnityEngine.Debug.Log("Keydown:" + vkCode);            
            switch (vkCode)
            {
                case 65:
                    Debug.Log("A");
                    break;
                case 66:
                    Debug.Log("B");
                    break;
                case 67:
                    Debug.Log("C");
                    break;
                case 68:
                    Debug.Log("D");
                    break;
                case 69:
                    Debug.Log("E");
                    break;
                case 70:
                    Debug.Log("F");
                    break;
                case 71:
                    Debug.Log("G");
                    break;
                case 72:
                    Debug.Log("H");
                    break;
                case 73:
                    Debug.Log("I");
                    break;
                case 74:
                    Debug.Log("J");
                    break;
                case 75:
                    Debug.Log("K");
                    break;
                case 76:
                    Debug.Log("L");
                    break;
                case 77:
                    Debug.Log("M");
                    break;
                case 78:
                    Debug.Log("N");
                    break;
                case 79:
                    Debug.Log("O");
                    break;
                case 80:
                    Debug.Log("P");
                    break;
                case 81:
                    Debug.Log("Q");
                    break;
                case 82:
                    Debug.Log("R");
                    break;
                case 83:
                    Debug.Log("S");
                    break;
                case 84:
                    Debug.Log("T");
                    break;
                case 85:
                    Debug.Log("U");
                    break;
                case 86:
                    Debug.Log("V");
                    break;
                case 87:
                    Debug.Log("W");
                    break;
                case 88:
                    Debug.Log("X");
                    break;
                case 89:
                    Debug.Log("Y");
                    break;
                case 90:
                    Debug.Log("Z");
                    break;
                default:
                    break;
            }
        }
        return CallNextHookEx(_hookID, nCode, wParam, lParam);//传给下一个钩子
    }
}

上方的脚本已经能够满足对键盘上26个按键的监听了。如果不够用，可以选择对照ASCII表进行补充!
特点：最后被按下并一直按住的键会不停输出，这在我所开发的项目中不合适

你也可以参考第二个写法，这里有鼠标相关的事件
脚本二：

//使用方式
	//1.在窗口 新建按钮（开始hook） 点击事件中执行Hook_Start
	//2.在窗口 新建按钮（关闭hook） 点击事件中执行Hook_Clear
	//3.在KeyBoardHookProc 中编写hook到键盘要进行的操作
	//4.在MouseHookProc 中编写hook到鼠标要进行的操作

	//一些依赖项
	[DllImport("user32.dll")]
	public static extern int SetWindowsHookEx(int idHook, HookProc lpfn, IntPtr hInstance, int threadId);
	
	[DllImport("user32.dll", CharSet = CharSet.Auto, CallingConvention = CallingConvention.StdCall)]
	public static extern bool UnhookWindowsHookEx(int idHook);
	
	[DllImport("user32.dll")]
	public static extern int CallNextHookEx(int idHook, int nCode, int wParam, IntPtr lParam);
	
	[DllImport("kernel32.dll")]
	public static extern int GetCurrentThreadId