Detecting text changes in Word 2016 from VSTO add-in

May 23, 2023 by Tarik Billa

Everthing should work fine if you don’t use a low-level hook in your VSTO add-in.

[DllImport("kernel32", CharSet = CharSet.Auto, SetLastError = true)]
public static extern int GetCurrentThreadId();

const int WH_KEYBOARD = 2;

private static IntPtr SetHook(HookProcedure procedure)
{
    var threadId = (uint)SafeNativeMethods.GetCurrentThreadId();
    return SetWindowsHookEx(WH_KEYBOARD, procedure, IntPtr.Zero, threadId);
}

Please note that you probably also need to create a hook to intercept mouse messages as it is possible to modify the text of a document solely by mouse interactions (e.g. copy and paste via Ribbon or context menu).

VSTO Sample

Here is a complete working VSTO sample including keyboard and mouse hooks:

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Runtime.InteropServices;
using System.Text;
using Office = Microsoft.Office.Core;

namespace SampleAddinWithKeyboardHook
{
    public partial class ThisAddIn
    {
        // NOTE: We need a backing field to prevent the delegate being garbage collected
        private SafeNativeMethods.HookProc _mouseProc;
        private SafeNativeMethods.HookProc _keyboardProc;

        private IntPtr _hookIdMouse;
        private IntPtr _hookIdKeyboard;

        private void ThisAddIn_Startup(object sender, EventArgs e)
        {
            _mouseProc = MouseHookCallback;
            _keyboardProc = KeyboardHookCallback;

            SetWindowsHooks();
        }

        private void ThisAddIn_Shutdown(object sender, EventArgs e)
        {
            UnhookWindowsHooks();
        }

        private void SetWindowsHooks()
        {
            uint threadId = (uint)SafeNativeMethods.GetCurrentThreadId();

            _hookIdMouse =
                SafeNativeMethods.SetWindowsHookEx(
                    (int)SafeNativeMethods.HookType.WH_MOUSE,
                    _mouseProc,
                    IntPtr.Zero,
                    threadId);

            _hookIdKeyboard =
                SafeNativeMethods.SetWindowsHookEx(
                    (int)SafeNativeMethods.HookType.WH_KEYBOARD,
                    _keyboardProc,
                    IntPtr.Zero,
                    threadId);
        }

        private void UnhookWindowsHooks()
        {
            SafeNativeMethods.UnhookWindowsHookEx(_hookIdKeyboard);
            SafeNativeMethods.UnhookWindowsHookEx(_hookIdMouse);
        }

        private IntPtr MouseHookCallback(int nCode, IntPtr wParam, IntPtr lParam)
        {
            if (nCode >= 0)
            {
                var mouseHookStruct =
                    (SafeNativeMethods.MouseHookStructEx)
                        Marshal.PtrToStructure(lParam, typeof(SafeNativeMethods.MouseHookStructEx));

                // handle mouse message here
                var message = (SafeNativeMethods.WindowMessages)wParam;
                Debug.WriteLine(
                    "{0} event detected at position {1} - {2}",
                    message,
                    mouseHookStruct.pt.X,
                    mouseHookStruct.pt.Y);
            }
            return SafeNativeMethods.CallNextHookEx(
                _hookIdKeyboard,
                nCode,
                wParam,
                lParam);
        }

        private IntPtr KeyboardHookCallback(int nCode, IntPtr wParam, IntPtr lParam)
        {
            if (nCode >= 0)
            {
                // handle key message here
                Debug.WriteLine("Key event detected.");
            }

            return SafeNativeMethods.CallNextHookEx(
                _hookIdKeyboard,
                nCode,
                wParam,
                lParam);
        }

        #region VSTO generated code

        /// <summary>
        /// Required method for Designer support.
        /// </summary>
        private void InternalStartup()
        {
            Startup += ThisAddIn_Startup;
            Shutdown += ThisAddIn_Shutdown;
        }

        #endregion
    }

    internal static class SafeNativeMethods
    {
        public delegate IntPtr HookProc(int nCode, IntPtr wParam, IntPtr lParam);

        public enum HookType
        {
            WH_KEYBOARD = 2,
            WH_MOUSE = 7
        }

        public enum WindowMessages : uint
        {
            WM_KEYDOWN = 0x0100,
            WM_KEYFIRST = 0x0100,
            WM_KEYLAST = 0x0108,
            WM_KEYUP = 0x0101,
            WM_LBUTTONDBLCLK = 0x0203,
            WM_LBUTTONDOWN = 0x0201,
            WM_LBUTTONUP = 0x0202,
            WM_MBUTTONDBLCLK = 0x0209,
            WM_MBUTTONDOWN = 0x0207,
            WM_MBUTTONUP = 0x0208,
            WM_MOUSEACTIVATE = 0x0021,
            WM_MOUSEFIRST = 0x0200,
            WM_MOUSEHOVER = 0x02A1,
            WM_MOUSELAST = 0x020D,
            WM_MOUSELEAVE = 0x02A3,
            WM_MOUSEMOVE = 0x0200,
            WM_MOUSEWHEEL = 0x020A,
            WM_MOUSEHWHEEL = 0x020E,
            WM_RBUTTONDBLCLK = 0x0206,
            WM_RBUTTONDOWN = 0x0204,
            WM_RBUTTONUP = 0x0205,
            WM_SYSDEADCHAR = 0x0107,
            WM_SYSKEYDOWN = 0x0104,
            WM_SYSKEYUP = 0x0105
        }

        [DllImport("kernel32.dll", CharSet = CharSet.Auto, SetLastError = true)]
        public static extern IntPtr GetModuleHandle(string lpModuleName);

        [DllImport("user32.dll", SetLastError = true)]
        public static extern bool UnhookWindowsHookEx(IntPtr hhk);

        [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
        public static extern IntPtr SetWindowsHookEx(
            int idHook,
            HookProc lpfn,
            IntPtr hMod,
            uint dwThreadId);

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

        [DllImport("kernel32", CharSet = CharSet.Auto, SetLastError = true)]
        public static extern int GetCurrentThreadId();

        [StructLayout(LayoutKind.Sequential)]
        public struct Point
        {
            public int X;
            public int Y;

            public Point(int x, int y)
            {
                X = x;
                Y = y;
            }

            public static implicit operator System.Drawing.Point(Point p)
            {
                return new System.Drawing.Point(p.X, p.Y);
            }

            public static implicit operator Point(System.Drawing.Point p)
            {
                return new Point(p.X, p.Y);
            }
        }

        [StructLayout(LayoutKind.Sequential)]
        public struct MouseHookStructEx
        {
            public Point pt;
            public IntPtr hwnd;
            public uint wHitTestCode;
            public IntPtr dwExtraInfo;
            public int MouseData;
        }
    }
}

VBE Add-in Sample

And here is a working sample for the VBA editor (VBE add-in):

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Runtime.InteropServices;
using System.Text;
using Extensibility;

namespace VbeAddin
{
    [ComVisible(true)]
    [ProgId("VbeAddin.Connect")]
    [Guid("95840C70-5A1A-4EDB-B436-40E8BF030469")]
    public class Connect : StandardOleMarshalObject, IDTExtensibility2
    {
        // NOTE: We need a backing field to prevent the delegate being garbage collected
        private SafeNativeMethods.HookProc _mouseProc;
        private SafeNativeMethods.HookProc _keyboardProc;

        private IntPtr _hookIdMouse;
        private IntPtr _hookIdKeyboard;

        #region IDTExtensibility2 Members

        public void OnConnection(object application, ext_ConnectMode connectMode, object addInInst, ref Array custom)
        {
            _mouseProc = MouseHookCallback;
            _keyboardProc = KeyboardHookCallback;

            SetWindowsHooks();
        }

        public void OnDisconnection(ext_DisconnectMode removeMode, ref Array custom)
        {
            UnhookWindowsHooks();
        }

        public void OnAddInsUpdate(ref Array custom)
        {
        }

        public void OnStartupComplete(ref Array custom)
        {
        }

        public void OnBeginShutdown(ref Array custom)
        {
        }

        #endregion

        private void SetWindowsHooks()
        {
            uint threadId = (uint)SafeNativeMethods.GetCurrentThreadId();

            _hookIdMouse =
                SafeNativeMethods.SetWindowsHookEx(
                    (int)SafeNativeMethods.HookType.WH_MOUSE,
                    _mouseProc,
                    IntPtr.Zero,
                    threadId);

            _hookIdKeyboard =
                SafeNativeMethods.SetWindowsHookEx(
                    (int)SafeNativeMethods.HookType.WH_KEYBOARD,
                    _keyboardProc,
                    IntPtr.Zero,
                    threadId);
        }

        private void UnhookWindowsHooks()
        {
            SafeNativeMethods.UnhookWindowsHookEx(_hookIdKeyboard);
            SafeNativeMethods.UnhookWindowsHookEx(_hookIdMouse);
        }

        private IntPtr MouseHookCallback(int nCode, IntPtr wParam, IntPtr lParam)
        {
            if (nCode >= 0)
            {
                var mouseHookStruct =
                    (SafeNativeMethods.MouseHookStructEx)
                        Marshal.PtrToStructure(
                            lParam,
                            typeof(SafeNativeMethods.MouseHookStructEx));

                // handle mouse message here
                var message = (SafeNativeMethods.WindowMessages)wParam;
                Debug.WriteLine(
                    "{0} event detected at position {1} - {2}",
                    message,
                    mouseHookStruct.pt.X,
                    mouseHookStruct.pt.Y);
            }
            return SafeNativeMethods.CallNextHookEx(
                _hookIdKeyboard,
                nCode,
                wParam,
                lParam);
        }

        private IntPtr KeyboardHookCallback(int nCode, IntPtr wParam, IntPtr lParam)
        {
            if (nCode >= 0)
            {
                // handle key message here
                Debug.WriteLine("Key event detected.");
            }
            return SafeNativeMethods.CallNextHookEx(
                _hookIdKeyboard,
                nCode,
                wParam,
                lParam);
        }
    }

    internal static class SafeNativeMethods
    {
        public delegate IntPtr HookProc(int nCode, IntPtr wParam, IntPtr lParam);

        public enum HookType
        {
            WH_KEYBOARD = 2,
            WH_MOUSE = 7
        }

        public enum WindowMessages : uint
        {
            WM_KEYDOWN = 0x0100,
            WM_KEYFIRST = 0x0100,
            WM_KEYLAST = 0x0108,
            WM_KEYUP = 0x0101,
            WM_LBUTTONDBLCLK = 0x0203,
            WM_LBUTTONDOWN = 0x0201,
            WM_LBUTTONUP = 0x0202,
            WM_MBUTTONDBLCLK = 0x0209,
            WM_MBUTTONDOWN = 0x0207,
            WM_MBUTTONUP = 0x0208,
            WM_MOUSEACTIVATE = 0x0021,
            WM_MOUSEFIRST = 0x0200,
            WM_MOUSEHOVER = 0x02A1,
            WM_MOUSELAST = 0x020D,
            WM_MOUSELEAVE = 0x02A3,
            WM_MOUSEMOVE = 0x0200,
            WM_MOUSEWHEEL = 0x020A,
            WM_MOUSEHWHEEL = 0x020E,
            WM_RBUTTONDBLCLK = 0x0206,
            WM_RBUTTONDOWN = 0x0204,
            WM_RBUTTONUP = 0x0205,
            WM_SYSDEADCHAR = 0x0107,
            WM_SYSKEYDOWN = 0x0104,
            WM_SYSKEYUP = 0x0105
        }

        [DllImport("kernel32.dll", CharSet = CharSet.Auto, SetLastError = true)]
        public static extern IntPtr GetModuleHandle(string lpModuleName);

        [DllImport("user32.dll", SetLastError = true)]
        public static extern bool UnhookWindowsHookEx(IntPtr hhk);

        [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
        public static extern IntPtr SetWindowsHookEx(
            int idHook,
            HookProc lpfn,
            IntPtr hMod,
            uint dwThreadId);

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

        [DllImport("kernel32", CharSet = CharSet.Auto, SetLastError = true)]
        public static extern int GetCurrentThreadId();

        [StructLayout(LayoutKind.Sequential)]
        public struct Point
        {
            public int X;
            public int Y;
        }

        [StructLayout(LayoutKind.Sequential)]
        public struct MouseHookStructEx
        {
            public Point pt;
            public IntPtr hwnd;
            public uint wHitTestCode;
            public IntPtr dwExtraInfo;
            public int MouseData;
        }
    }
}

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