How can I check and toggle Num-Lock programmatically in C#?

Question

I would like to programmatically check the value of, and be able to toggle num-lock. What's the simplest way to do that in C#?

The reason is that I want to verify num-lock is "ON" at program start.

Thanks

Answer 1

Check How to programmatically turn on the Numlock Key

using System;
using System.Runtime.InteropServices;

class SetNumlockKeyOn
{
    [StructLayout(LayoutKind.Sequential)]
    public struct INPUT
    {
        internal int type;
        internal short wVk;
        internal short wScan;
        internal int dwFlags;
        internal int time;
        internal IntPtr dwExtraInfo;
        int dummy1;
        int dummy2;
        internal int type1;
        internal short wVk1;
        internal short wScan1;
        internal int dwFlags1;
        internal int time1;
        internal IntPtr dwExtraInfo1;
        int dummy3;
        int dummy4;
}
[DllImport(“user32.dll”)]
static extern int SendInput(uint nInputs, IntPtr pInputs, int cbSize);

public static void SetNumlockOn()
{
    const int mouseInpSize = 28;//Hardcoded size of the MOUSEINPUT tag !!!
    INPUT input = new INPUT();
    input.type = 0x01; //INPUT_KEYBOARD
    input.wVk = 0x90; //VK_NUMLOCK
    input.wScan = 0;
    input.dwFlags = 0; //key-down
    input.time = 0;
    input.dwExtraInfo = IntPtr.Zero;

    input.type1 = 0x01;
    input.wVk1 = 0x90;
    input.wScan1 = 0;
    input.dwFlags1 = 2; //key-up
    input.time1 = 0;
    input.dwExtraInfo1 = IntPtr.Zero;

    IntPtr pI = Marshal.AllocHGlobal(mouseInpSize * 2);
    Marshal.StructureToPtr(input, pI, false);
    int result = SendInput(2, pI, mouseInpSize); //Hardcoded size of the MOUSEINPUT tag !!!

    //if (result == 0 || Marshal.GetLastWin32Error() != 0)
    // Console.WriteLine(Marshal.GetLastWin32Error());
    Marshal.FreeHGlobal(pI);
}

Answer 2

You can do this via P/Invoke with GetKeyboardState and keybd_event.

The MSDN page for keybd_event shows exactly how to toggle num-lock, as well as get it's state (in C++).

There are P/Invoke signitures available on pinvoke.net for keybd_event and GetKeyboardState.

Answer 3

In addition to the answer given by Arsen:

There are problems with heap corruption in 64-bit builds. Programs using this code may crash at any point. To see this, enable the debug option "Enable Windows debug heap allocator". The debugger stops on calling FreeHGlobal.

It helps to calculate the size of the INPUT structure as follows.

int mouseInpSize = Marshal.SizeOf(input);
IntPtr pI = Marshal.AllocHGlobal(mouseInpSize);
Marshal.StructureToPtr(input, pI, false);
int result = SendInput(2, pI, mouseInpSize);
Marshal.FreeHGlobal(pI);