Excel VSTO Key hook

Question

I want to change cell color when Enter key is pressed. Everything is fine except, that code doesn\'t work in active Excel 2013, only when it is in background. H

Answer 1

The main mistake you made in your code is using WH_KEYBOARD_LL. It will not work well in Excel, use WH_KEYBOARD instead. The code below allows you to catch any key pressed, check modifiers and invoke some action.

using System;
using System.Runtime.InteropServices;
using System.Windows.Forms;
using Microsoft.Office.Interop.Excel;

namespace SimpleExcelAddIn {
    static class ShortcutManager {
        delegate int LowLevelKeyboardProc(int nCode, IntPtr wParam, IntPtr lParam);
        static readonly LowLevelKeyboardProc _proc = HookCallback;
        static IntPtr _hookID = IntPtr.Zero;
        const int WH_KEYBOARD = 2;
        const int HC_ACTION = 0;
        [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
        static extern IntPtr SetWindowsHookEx(int idHook, LowLevelKeyboardProc lpfn, IntPtr hMod, uint dwThreadId);
        [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
        static extern bool UnhookWindowsHookEx(IntPtr idHook);
        [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
        static extern IntPtr CallNextHookEx(IntPtr hhk, int nCode, IntPtr wParam, IntPtr lParam);
        [DllImport("user32.dll")]
        static extern short GetKeyState(int nVirtKey);

        static bool _keyHookingStarted;
        public static void Start() {
            if (!_keyHookingStarted) {
#pragma warning disable 0618
                _hookID = SetWindowsHookEx(WH_KEYBOARD, _proc, IntPtr.Zero, (uint) AppDomain.GetCurrentThreadId());
#pragma warning restore 0618
                _keyHookingStarted = true;
            }
        }
        public static void Stop() {
            if (_keyHookingStarted) {
                UnhookWindowsHookEx(_hookID);
                _hookID = IntPtr.Zero;
                _keyHookingStarted = false;
            }
        }
        static void OnKeyPress(uint keys) {
            Func<Keys, bool> checkKey = key => keys == (uint) key && IsKeyDown(key);

            //checks that shift, alt, ctrl and win keys are not pressed
            Func<bool> checkModifiers = () => !IsKeyDown(Keys.ShiftKey)
                && !IsKeyDown(Keys.Menu) // Keys.Menu is Alt button code
                && !IsKeyDown(Keys.LWin) && !IsKeyDown(Keys.RWin);

            if (checkModifiers() && (checkKey(Keys.Enter) || checkKey(Keys.Return))) {
                // Make you actions here. If it is some long action, do it in background thread
                // this code is just and example
                Worksheet ws = Globals.ThisAddIn.Application.ActiveSheet;
                Range cell = ws.Cells[1, 1];
                cell.Interior.Color = 0xFF0000;
            }
        }
        static bool IsKeyDown(Keys keys) {
            return (GetKeyState((int) keys) & 0x8000) == 0x8000;
        }
        static int HookCallback(int nCode, IntPtr wParam, IntPtr lParam) {
            if (nCode < 0) {
                return (int) CallNextHookEx(_hookID, nCode, wParam, lParam);
            }
            if (nCode == HC_ACTION) {
                OnKeyPress((uint) wParam);
            }
            return (int) CallNextHookEx(_hookID, nCode, wParam, lParam);
        }
    }
}

To use this class, call Start() and Stop() methods.