黑客来了。。。键盘钩子，听起来很高端。

首先是这个公共的类：globalKeyboardHook.cs

using System;
using System.Collections.Generic;
using System.Text;
using System.Runtime.InteropServices;
using System.Windows.Forms;

namespace Utilities {
    /// <summary>
    /// A class that manages a global low level keyboard hook
    /// </summary>
    class globalKeyboardHook {
        #region Constant, Structure and Delegate Definitions
        /// <summary>
        /// defines the callback type for the hook
        /// </summary>
        public delegate int keyboardHookProc(int code, int wParam, ref keyboardHookStruct lParam);

        public struct keyboardHookStruct {
            public int vkCode;
            public int scanCode;
            public int flags;
            public int time;
            public int dwExtraInfo;
        }

        const int WH_KEYBOARD_LL = 13;
        const int WM_KEYDOWN = 0x100;
        const int WM_KEYUP = 0x101;
        const int WM_SYSKEYDOWN = 0x104;
        const int WM_SYSKEYUP = 0x105;
        #endregion

        #region Instance Variables
        /// <summary>
        /// The collections of keys to watch for
        /// </summary>
        public List<Keys> HookedKeys = new List<Keys>();
        /// <summary>
        /// Handle to the hook, need this to unhook and call the next hook
        /// </summary>
        IntPtr hhook = IntPtr.Zero;
        #endregion

        #region Events
        /// <summary>
        /// Occurs when one of the hooked keys is pressed
        /// </summary>
        public event KeyEventHandler KeyDown;
        /// <summary>
        /// Occurs when one of the hooked keys is released
        /// </summary>
        public event KeyEventHandler KeyUp;
        #endregion

        #region Constructors and Destructors
        /// <summary>
        /// Initializes a new instance of the <see cref="globalKeyboardHook"/> class and installs the keyboard hook.
        /// </summary>
        public globalKeyboardHook() {
            hook();
        }

        /// <summary>
        /// Releases unmanaged resources and performs other cleanup operations before the
        /// <see cref="globalKeyboardHook"/> is reclaimed by garbage collection and uninstalls the keyboard hook.
        /// </summary>
        ~globalKeyboardHook() {
            unhook();
        }
        #endregion

        #region Public Methods
        /// <summary>
        /// Installs the global hook
        /// </summary>
        public void hook() {
            IntPtr hInstance = LoadLibrary("User32");
            hhook = SetWindowsHookEx(WH_KEYBOARD_LL, hookProc, hInstance, 0);
        }

        /// <summary>
        /// Uninstalls the global hook
        /// </summary>
        public void unhook() {
            UnhookWindowsHookEx(hhook);
        }

        /// <summary>
        /// The callback for the keyboard hook
        /// </summary>
        /// <param name="code">The hook code, if it isn‘t >= 0, the function shouldn‘t do anyting</param>
        /// <param name="wParam">The event type</param>
        /// <param name="lParam">The keyhook event information</param>
        /// <returns></returns>
        public int hookProc(int code, int wParam, ref keyboardHookStruct lParam) {
            if (code >= 0) {
                Keys key = (Keys)lParam.vkCode;
                if (HookedKeys.Contains(key)) {
                    KeyEventArgs kea = new KeyEventArgs(key);
                    if ((wParam == WM_KEYDOWN || wParam == WM_SYSKEYDOWN) && (KeyDown != null)) {
                        KeyDown(this, kea) ;
                    } else if ((wParam == WM_KEYUP || wParam == WM_SYSKEYUP) && (KeyUp != null)) {
                        KeyUp(this, kea);
                    }
                    if (kea.Handled)
                        return 1;
                }
            }
            return CallNextHookEx(hhook, code, wParam, ref lParam);
        }
        #endregion

        #region DLL imports
        /// <summary>
        /// Sets the windows hook, do the desired event, one of hInstance or threadId must be non-null
        /// </summary>
        /// <param name="idHook">The id of the event you want to hook</param>
        /// <param name="callback">The callback.</param>
        /// <param name="hInstance">The handle you want to attach the event to, can be null</param>
        /// <param name="threadId">The thread you want to attach the event to, can be null</param>
        /// <returns>a handle to the desired hook</returns>
        [DllImport("user32.dll")]
        static extern IntPtr SetWindowsHookEx(int idHook, keyboardHookProc callback, IntPtr hInstance, uint threadId);

        /// <summary>
        /// Unhooks the windows hook.
        /// </summary>
        /// <param name="hInstance">The hook handle that was returned from SetWindowsHookEx</param>
        /// <returns>True if successful, false otherwise</returns>
        [DllImport("user32.dll")]
        static extern bool UnhookWindowsHookEx(IntPtr hInstance);

        /// <summary>
        /// Calls the next hook.
        /// </summary>
        /// <param name="idHook">The hook id</param>
        /// <param name="nCode">The hook code</param>
        /// <param name="wParam">The wparam.</param>
        /// <param name="lParam">The lparam.</param>
        /// <returns></returns>
        [DllImport("user32.dll")]
        static extern int CallNextHookEx(IntPtr idHook, int nCode, int wParam, ref keyboardHookStruct lParam);

        /// <summary>
        /// Loads the library.
        /// </summary>
        /// <param name="lpFileName">Name of the library</param>
        /// <returns>A handle to the library</returns>
        [DllImport("kernel32.dll")]
        static extern IntPtr LoadLibrary(string lpFileName);
        #endregion
    }
}

调用方式：

public partial class Form1 : Form {
        globalKeyboardHook gkh = new globalKeyboardHook();

        public Form1() {
            InitializeComponent();
        }
        [DllImport("user32.dll")]
        public static extern int FindWindow(
            string lpClassName, // class name
            string lpWindowName // window name
        );

        [DllImport("user32.dll")]
        public static extern int SetForegroundWindow(
            int hWnd // handle to window
            );
        private void Form1_Load(object sender, EventArgs e) {
            gkh.HookedKeys.Add(Keys.A);
            gkh.HookedKeys.Add(Keys.B);
            gkh.KeyDown += new KeyEventHandler(gkh_KeyDown);
            gkh.KeyUp += new KeyEventHandler(gkh_KeyUp);
        }

        void gkh_KeyUp(object sender, KeyEventArgs e) {
            lstLog.Items.Add("Up\t" + e.KeyCode.ToString());
            int iHandle = FindWindow(null, "1 - Notepad");

            SetForegroundWindow(iHandle);

            string keys = "Z";//Here is the keys you want to send.

            System.Windows.Forms.SendKeys.Send(keys);
            e.Handled = true;
        }

        void gkh_KeyDown(object sender, KeyEventArgs e) {
            lstLog.Items.Add("Down\t" + e.KeyCode.ToString());
            e.Handled = true;
        }
    }

效果自己测吧，直接可以改另一个app的触发事件。