gistfile1.cs

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

class KeyDownPreview
{
    #region Initialization

    private IntPtr Hook = IntPtr.Zero;

    private event KeyEventHandler KeyDown, KeyUp;

    [DllImport("user32.dll")]
    static extern IntPtr SetWindowsHookEx(int idHook, KeyboardHookProcess callback, IntPtr hInstance, uint threadId);

    [DllImport("user32.dll")]
    static extern bool UnhookWindowsHookEx(IntPtr hInstance);

    [DllImport("user32.dll")]
    static extern int CallNextHookEx(IntPtr idHook, int nCode, int wParam, ref KeyboardHookStruct lParam);

    [DllImport("kernel32.dll")]
    static extern IntPtr LoadLibrary(string lpFileName);

    public struct KeyboardHookStruct
    {
        public int KeyCode, ScanCode, Flags, Time, DwExtraInfo;
    }

    private delegate int KeyboardHookProcess(int code, int wParam, ref KeyboardHookStruct lParam);

    private const int WH_KEYBOARD_LL = 13, WM_KEYDOWN = 0x100, WM_KEYUP = 0x101, WM_SYSKEYDOWN = 0x104, WM_SYSKEYUP = 0x105;

    #endregion

    #region Main

    public KeyDownPreview()
    {
        var hInstance = LoadLibrary("User32");
        Hook = SetWindowsHookEx(WH_KEYBOARD_LL, HookProccess, hInstance, 0);
    }

    ~KeyDownPreview()
    {
        UnhookWindowsHookEx(Hook);
    }

    public int HookProccess(int code, int wParam, ref KeyboardHookStruct lParam)
    {
        if (code >= 0)
        {
            var kea = new KeyEventArgs((Keys)lParam.KeyCode);

            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(Hook, code, wParam, ref lParam);
    }

    #endregion
}