How to make a global keyboard hook in C#

Question

How can I make a global keyboard hook for an Electron.NET app in C#? I believe as long as it works in a console app it should work properly in an Electron.Net app.

I made a 'solution' for this problem, but It tends to use up a lot of CPU (7-10%). Maybe someone is somehow able to make it actually efficient if there is no other option:

using System;
using System.Runtime.InteropServices;
using System.Threading;

[DllImport("User32.dll")]
public static extern short GetAsyncKeyState(int vKey);

// Other VKey codes: https://learn.microsoft.com/en-us/windows/win32/inputdev/virtual-key-codes
public enum VKeys {
    LBUTTON = 0x01,     // Left mouse button
    RBUTTON = 0x02,     // Right mouse button
    KEY_0 = 0x30,       // 0 key
    KEY_1 = 0x31,       // 1 key
    KEY_2 = 0x32,       // 2 key
    KEY_3 = 0x33,       // 3 key
    KEY_4 = 0x34,       // 4 key
    KEY_5 = 0x35,       // 5 key
    KEY_6 = 0x36,       // 6 key
    KEY_7 = 0x37,       // 7 key
    KEY_8 = 0x38,       // 8 key
    KEY_9 = 0x39        // 9 key
}

public void Start()
{
    Thread HookThread = new Thread(delegate ()
    {
        var keys = Enum.GetValues(typeof(VKeys));

        while (true)
        {
            foreach (int key in keys)
            {
                var ks = GetAsyncKeyState(key);

                if (ks < 0)
                {
                    Console.WriteLine($"pressed {key}");
                    //Thread.Sleep(100);
                }

                //Thread.Sleep(1); // Even sleeping for '1ms' will delay it too much
            }
        }
    });

    HookThread.Start();
}

A lot of things I found would only work if I was using WinForms or WPF.

Edit:

I tried this answer by hanabanashiku, and a lot of others that I found online, but all of them seemed to just lag the keyboards input and their callback functions would seem to be never called.

I decided to write the keyboard hook in C++, compile as a DLL and then reference that DLL in my C# code to hopefully make a keyboard hook that functioned properly and didn't cause any noticeable input lag, but that didn't work either.

The keyboard hook ran perfectly when run as an .exe in C++, but when I compiled it as a DLL and ran it in C# it caused the same issue as before - a lot of input lag and the callback function seemingly not being called.

Heres the code if anyone wants to try it:

KeyboardHook.cpp

#include "KeyboardHook.h"
#include <iostream>

#define __event void KeyDown(int key), KeyUp(int key);

using namespace Hooks;

void KeyDown(int key)
{
    std::cout << "KeyDown\n";
}

void KeyUp(int key)
{
    std::cout << "KeyUp\n";
}

LRESULT CALLBACK KeyboardProc(int nCode, WPARAM wParam, LPARAM lParam)
{
    if (nCode == HC_ACTION)
    {
        PKBDLLHOOKSTRUCT p = (PKBDLLHOOKSTRUCT)lParam;

        switch (wParam)
        {
            case WM_KEYDOWN:
            case WM_SYSKEYDOWN:
                KeyDown(p->vkCode);
                break;
            case WM_KEYUP:
            case WM_SYSKEYUP:
                KeyUp(p->vkCode);
                break;
        }
    }

    // Not processing keys so always return CallNextHookEx
    return(CallNextHookEx(NULL, nCode, wParam, lParam));
}

void KeyboardHook::Install() {
    // Install keyboard hook
    keyboardHook = SetWindowsHookEx(WH_KEYBOARD_LL, KeyboardProc, 0, 0);
    std::cout << "Installed\n";
}

void KeyboardHook::Uninstall() {
    // Unhook keyboard hook
    UnhookWindowsHookEx(keyboardHook);
}

KeyboardHook.h

#include <Windows.h>

HHOOK keyboardHook;

namespace Hooks 
{
    class KeyboardHook
    {
    public:
        __declspec(dllexport) void Install();
        __declspec(dllexport) void Uninstall();
    };
}

Program.cs

using System;
using System.Runtime.InteropServices;

namespace HelloMyNameIsSpindiNiceToMeetYou
{
    class Program
    {
        private const string hooksPath = @"C:\Path\To\Hooks.dll";

        // If EntryPoint doesn't work, yours might be different
        // https://learn.microsoft.com/en-us/dotnet/framework/interop/identifying-functions-in-dlls
        //
        // "For example, you can use dumpbin /exports Hooks.dll [...] to obtain function names." 
        // you need to be in the folder with the dll for above to work in Command Prompt for VS
        [DllImport(hooksPath, EntryPoint = "?Install@KeyboardHook@Hooks@@QEAAXXZ", CallingConvention = CallingConvention.Cdecl)]
        private extern static void Install();

        static void Main(string[] args)
        {
            Install();

            // keep console app running
            while (true)
            {
                continue;
            }

            // or keep it running with this
            // Console.ReadKey();
        }
    }
}

I am testing this stuff outside of an electron.net app now, just in a console app and things still don't work. Everything I have found just leads back to using winforms, which I cannot use.

Answer 1

Electron has a way to create global shortcuts built-in, you just have to adapt the syntax a little to work with Electron.Net, you can search the repo to figure out function names (usually names are the same, just in PascalCase).

Registering a shortcut:

Electron.GlobalShortcut.Register("CommandOrControl+X", () =>
{
    Console.WriteLine("CommandOrControl+X pressed");
});

Unregistering a shortcut:

// Unregister specific shortcut
Electron.GlobalShortcut.Unregister("CommandOrControl+X");

// Unregister all shortcuts
Electron.GlobalShortcut.UnregisterAll();

Answer 2

Your solution uses a lot of computing power, because every time the loop repeats, it's making 11 calls to the Windows API. To more efficiently accomplish this, you will want to add a keyboard hook. A simple solution would be something like the following.

[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);

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

private const int WH_KEYBOARD_LL = 13;
private const int WM_KEYDOWN = 0x0100;
private delegate IntPtr LowLevelKeyboardProc(int nCode, IntPtr wParam, IntPtr lParam);


private static InPtr hook_ = IntPtr.Zero;
private static LowLevelHookProc _proc = KeyboardProc;

public void Start() {
    using (var process = Process.GetCurrentProcess())
        using (var module = process.MainModule)
        {
            _hook = SetWindowsHookEx(WH_KEYBOARD_LL, _proc,
                GetModuleHandle(module.ModuleName), 0);
        }

private static IntPtr KeyboardProc(int nCode, IntPtr wParam, IntPtr lParam)
    {
        if (nCode >= 0 && wParam == (IntPtr)WM_KEYDOWN) {
            switch(nCode) {
                 // Look for keys
            }
        }

        return CallNextHookEx(_hookID, nCode, wParam, lParam);
    }

The Callback function will fire every time a key is pressed down. Simply look for the virtual keys that you wish to query.