Recently I came across a problem where a customer was looking for the ways to call a function in an VSTO office add-in using keyboard shortcuts. Since I could not find good documentation on it, I decided to document my findings.

One can implement these in following ways:
1.    Use KeyBindings
2.    Hook the main window and trap the key combinations to launch custom functions.

Using KeyBindings

KeyBindings can be used to assign keyboard shortcuts to macros. Then macros can be used to call the function in managed add-in. I found following are few useful links which talk about the VSTO-VBA integration.

VSTO VBA integration: http://msdn.microsoft.com/en-us/magazine/cc163373.aspx
Calling VSTO code from VBA: http://msdn.microsoft.com/en-us/office/cc178910.aspx
KeyBindings Collection: http://msdn.microsoft.com/en-us/library/bb211991(v=office.12).aspx.

Using Keyboard Hook

This can also be achieved using Windows Hooks(http://msdn.microsoft.com/en-us/library/ms997537.aspx)

Following is a sample class which traps Ctrl+1 keys and writes "A" in A4 cell in Excel (I used this class in a VSTO Excel addin project). This class uses local hook to trap Ctrl+1 keys. It can be used to set hook (by calling its SetHook function), release hook (by calling its ReleaseHook function).

using System;
using System.Diagnostics;
using System.Windows.Forms;
using System.Runtime.InteropServices;
using Microsoft.Office.Core;
using Microsoft.Office.Interop.Excel;
using Excel = Microsoft.Office.Interop.Excel;
 
namespace Hooking
{
	public class InterceptKeys
	{
		public delegate int LowLevelKeyboardProc(int nCode, IntPtr wParam, IntPtr lParam);
		private static LowLevelKeyboardProc _proc = HookCallback;
		private static IntPtr _hookID = IntPtr.Zero;
		private static Microsoft.Office.Tools.CustomTaskPane ctpRef = null;
 
		//Declare the mouse hook constant.
		//For other hook types, you can obtain these values from Winuser.h in the Microsoft SDK. 
		private const int WH_KEYBOARD = 2;
		private const int HC_ACTION = 0;
		public static void SetHook()
		{
			_hookID = SetWindowsHookEx(WH_KEYBOARD, _proc, IntPtr.Zero, (uint)AppDomain.GetCurrentThreadId());
		}

		public static void ReleaseHook()
		{
			UnhookWindowsHookEx(_hookID);
		}

		private static int HookCallback(int nCode, IntPtr wParam, IntPtr lParam)
		{
			if (nCode < 0)
			{
				return (int)CallNextHookEx(_hookID, nCode, wParam, lParam);
			}
			else
			{
				if (nCode == HC_ACTION)
				{
					Keys keyData = (Keys)wParam;
					if (Functions.IsKeyDown(Keys.ControlKey) && keyData == Keys.D1)
					{
						object missing = System.Reflection.Missing.Value;
						Excel.Workbook exBook = Excel_CustomTaskPane_ACC.Globals.ThisAddIn.Application.ActiveWorkbook;    
						Excel.Worksheet exSheet = (Excel.Worksheet)exBook.ActiveSheet;
						exSheet.get_Range("A4", missing).Value2 = "A";
					}
				}
				return (int)CallNextHookEx(_hookID, nCode, wParam, lParam); 
			}
		}
 
		[DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
		private static extern IntPtr SetWindowsHookEx(int idHook, LowLevelKeyboardProc lpfn, IntPtr hMod, uint dwThreadId);
 
		[DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
		[return: MarshalAs(UnmanagedType.Bool)]
		private static extern bool UnhookWindowsHookEx(IntPtr hhk);

		[DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
		private static extern IntPtr CallNextHookEx(IntPtr hhk, int nCode,IntPtr wParam, IntPtr lParam);
	}

	public class Functions
	{
		public static bool IsKeyDown(Keys keys)
		{
			return (GetKeyState((int)keys) & 0x8000) == 0x8000;
		}

		[DllImport("user32.dll")]
		static extern short GetKeyState(int nVirtKey);
	}
}