private void FrmMain_KeyDown(object sender, KeyEventArgs e)

        {if (e.Alt && e.Shift && e.Control && e.KeyCode == Keys.S){MessageBox.Show("我按了Control +Shift +Alt +S");}}

  public class AppHotKey{[DllImport("kernel32.dll")]public static extern uint GetLastError();//如果函数执行成功，返回值不为0。//如果函数执行失败，返回值为0。要得到扩展错误信息，调用GetLastError。[DllImport("user32.dll", SetLastError = true)]public static extern bool RegisterHotKey(IntPtr hWnd,                //要定义热键的窗口的句柄int id,                     //定义热键ID（不能与其它ID重复）           KeyModifiers fsModifiers,   //标识热键是否在按Alt、Ctrl、Shift、Windows等键时才会生效Keys vk                     //定义热键的内容
            );[DllImport("user32.dll", SetLastError = true)]public static extern bool UnregisterHotKey(IntPtr hWnd,                //要取消热键的窗口的句柄int id                      //要取消热键的ID
            );//定义了辅助键的名称（将数字转变为字符以便于记忆，也可去除此枚举而直接使用数值）
        [Flags()]public enum KeyModifiers{None = 0,Alt = 1,Ctrl = 2,Shift = 4,WindowsKey = 8}/// <summary>/// 注册热键/// </summary>/// <param name="hwnd">窗口句柄</param>/// <param name="hotKey_id">热键ID</param>/// <param name="keyModifiers">组合键</param>/// <param name="key">热键</param>public static void RegKey(IntPtr hwnd, int hotKey_id, KeyModifiers keyModifiers, Keys key){try{if (!RegisterHotKey(hwnd, hotKey_id, keyModifiers, key)){if (Marshal.GetLastWin32Error() == 1409) { MessageBox.Show("热键被占用 ！"); }else{MessageBox.Show("注册热键失败！");}}}catch (Exception) { }}/// <summary>/// 注销热键/// </summary>/// <param name="hwnd">窗口句柄</param>/// <param name="hotKey_id">热键ID</param>public static void UnRegKey(IntPtr hwnd, int hotKey_id){//注销Id号为hotKey_id的热键设定
            UnregisterHotKey(hwnd, hotKey_id);}}

 　　    private const int WM_HOTKEY = 0x312; //窗口消息-热键private const int WM_CREATE = 0x1; //窗口消息-创建private const int WM_DESTROY = 0x2; //窗口消息-销毁private const int Space = 0x3572; //热键IDprotected override void WndProc(ref Message m){base.WndProc(ref m);switch (m.Msg){case WM_HOTKEY: //窗口消息-热键IDswitch (m.WParam.ToInt32()){case Space: //热键ID
                            MessageBox.Show("我按了Control +Shift +Alt +S");break;default:break;}break;case WM_CREATE: //窗口消息-创建
                    AppHotKey.RegKey(Handle, Space, AppHotKey.KeyModifiers.Ctrl | AppHotKey.KeyModifiers.Shift | AppHotKey.KeyModifiers.Alt, Keys.S);break;case WM_DESTROY: //窗口消息-销毁
                    AppHotKey.UnRegKey(Handle, Space); //销毁热键break;default:break;}}