How can I capture modifier (ctrl, alt, shift) key presses as a single key press in a C# console app?

Question

Console.ReadKey will only capture input when a "normal" key is pressed, and then it attaches the modifiers (if any) as a part of the key info. How can I register a single modifier key press as an input?

Answer 1

One solution is offered in this link. I do some edit on the mentioned code for as an answer to your question.

To run this code:

1. Create a Console Application
2. Add reference to System.Windows.Forms.dll assembly
3. Paste this code and test.

Code:

using System;
using System.Diagnostics;
using System.Windows.Forms;
using System.Runtime.InteropServices;

class Program
{
    class InterceptKeys
    {
        // https://blogs.msdn.microsoft.com/toub/2006/05/03/low-level-keyboard-hook-in-c/
        private const int WH_KEYBOARD_LL = 13;
        private const int WM_KEYDOWN = 0x0100;
        private static LowLevelKeyboardProc _proc = HookCallback;
        private static IntPtr _hookID = IntPtr.Zero;
        private static IntPtr SetHook(LowLevelKeyboardProc proc)
        {
            using (Process curProcess = Process.GetCurrentProcess())
            using (ProcessModule curModule = curProcess.MainModule)
            {
                return SetWindowsHookEx(WH_KEYBOARD_LL, proc,
                    GetModuleHandle(curModule.ModuleName), 0);
            }
        }

        private delegate IntPtr LowLevelKeyboardProc(int nCode, IntPtr wParam, IntPtr lParam);

        private static IntPtr HookCallback(int nCode, IntPtr wParam, IntPtr lParam)
        {
            if (nCode >= 0 && wParam == (IntPtr)WM_KEYDOWN)
            {
                int vkCode = Marshal.ReadInt32(lParam);
                OnKeyDown?.Invoke(new KeyEventArgs((Keys)vkCode));
            }
            return 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);

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

        private static event OnKeyDownDelegate OnKeyDown = null;
        public delegate void OnKeyDownDelegate(KeyEventArgs e);
        public static void SetupHook(OnKeyDownDelegate OnKeyDown)
        {
            InterceptKeys.OnKeyDown = OnKeyDown;
            System.Threading.Tasks.Task.Run(() =>
            {
                _hookID = SetHook(_proc);
                Application.Run();
                UnhookWindowsHookEx(_hookID);
            });
        }

        public static void ReleaseHook()
        {
            Application.Exit();
        }
    }

    static void KeyDown(KeyEventArgs e)
    {
        Console.WriteLine("Hook: "+ e.KeyCode);
    }

    static void Main()
    {
        InterceptKeys.SetupHook(KeyDown);
        while (true)
        {
            ConsoleKey key = Console.ReadKey(true).Key;
            Console.WriteLine("ReadKey: "+ key);

            if (key == ConsoleKey.Escape)
                break;
        }
        InterceptKeys.ReleaseHook();
    }
}