In order to know whether or not Caps Lock, Num Lock or Scroll Lock keys are on, we need to make use of the Win32 API through a call to an unmanaged function.

Since we’ll make a call to an unmanaged function, the following using statement is in order:

using System.Runtime.InteropServices;
The following is the definition for the unmanaged function we’ll be using, GetKeyState():

// An umanaged function that retrieves the states of each key

[DllImport("user32.dll", CharSet = CharSet.Auto, ExactSpelling = true, CallingConvention = CallingConvention.Winapi)]

public static extern short GetKeyState(int keyCode);

And finally we retrieve the state of each of the three keys and show it in a message box:

// Get they key state and store it as bool

bool CapsLock = (((ushort)GetKeyState(0x14)) & 0xffff) != 0;

bool NumLock = (((ushort)GetKeyState(0x90)) & 0xffff) != 0;

bool ScrollLock = (((ushort)GetKeyState(0x91)) & 0xffff) != 0;

 

// Show the status

MessageBox.Show("Caps Lock is on: " + CapsLock.ToString());

MessageBox.Show("Num Lock is on: " + NumLock.ToString());

MessageBox.Show("Scroll Lock is on: " + ScrollLock.ToString());

Here is the complete source code:

using System;

using System.Collections.Generic;

using System.ComponentModel;

using System.Data;

using System.Drawing;

using System.Text;

using System.Windows.Forms;

using System.Runtime.InteropServices;

 

namespace Labs

{

    public partial class Form1 : Form


    {

        public Form1()

        {

            InitializeComponent();

        }

        // An umanaged function that retrieves the states of each key

        [DllImport("user32.dll", CharSet = CharSet.Auto, ExactSpelling = true, CallingConvention = CallingConvention.Winapi)]

        public static extern short GetKeyState(int keyCode);

 

        private void Form1_Load(object sender, EventArgs e)

        {

            // Get they key state and store it as bool

            bool CapsLock = (((ushort)GetKeyState(0x14)) & 0xffff) != 0;

            bool NumLock = (((ushort)GetKeyState(0x90)) & 0xffff) != 0;

            bool ScrollLock = (((ushort)GetKeyState(0x91)) & 0xffff) != 0;

 

            // Show the status

            MessageBox.Show("Caps Lock is on: " + CapsLock.ToString());

            MessageBox.Show("Num Lock is on: " + NumLock.ToString());

            MessageBox.Show("Scroll Lock is on: " + ScrollLock.ToString());

        }

    }

}