Set global hotkeys using C#

I need to capture a key press when my program is not in focus. (ie. Ctrl+Alt+J) and trigger an event in my program.

Thus far i have found this dll that appears to be the correct path"

[DllImport("user32.dll")]private static extern int RegisterHotKey(IntPtr hwnd, int id,int fsModifiers, int vk);

[DllImport("user32.dll")] private static extern int UnregisterHotKey(IntPtr hwnd, int id);

Please note that this code will not trigger events in console application projects. You have to use WinForms project for events to fire.

This is the correct code:

public sealed  class KeyboardHook : IDisposable
{
    // Registers a hot key with Windows.
    [DllImport("user32.dll")]
    private static extern bool RegisterHotKey(IntPtr hWnd, int id, uint fsModifiers, uint vk);
    // Unregisters the hot key with Windows.
    [DllImport("user32.dll")]
    private static extern bool UnregisterHotKey(IntPtr hWnd, int id);

    /// <summary>
    /// Represents the window that is used internally to get the messages.
    /// </summary>
    private class Window : NativeWindow, IDisposable
    {
        private static int WM_HOTKEY = 0x0312;

        public Window()
        {
            // create the handle for the window.
            this.CreateHandle(new CreateParams());
        }

        /// <summary>
        /// Overridden to get the notifications.
        /// </summary>
        /// <param name="m"></param>
        protected override void WndProc(ref Message m)
        {
            base.WndProc(ref m);

            // check if we got a hot key pressed.
            if (m.Msg == WM_HOTKEY)
            {
                // get the keys.
                Keys key = (Keys)(((int)m.LParam >> 16) & 0xFFFF);
                ModifierKeys modifier = (ModifierKeys)((int)m.LParam & 0xFFFF);

                // invoke the event to notify the parent.
                if (KeyPressed != null)
                    KeyPressed(this, new KeyPressedEventArgs(modifier, key));
            }
        }

        public event EventHandler<KeyPressedEventArgs> KeyPressed;

        #region IDisposable Members

        public void Dispose()
        {
            this.DestroyHandle();
        }

        #endregion
    }

    private Window _window = new Window();
    private int _currentId;

    public KeyboardHook()
    {
        // register the event of the inner native window.
        _window.KeyPressed += delegate(object sender, KeyPressedEventArgs args)
        {
            if (KeyPressed != null)
                KeyPressed(this, args);
        };
    }

    /// <summary>
    /// Registers a hot key in the system.
    /// </summary>
    /// <param name="modifier">The modifiers that are associated with the hot key.</param>
    /// <param name="key">The key itself that is associated with the hot key.</param>
    public void RegisterHotKey(ModifierKeys modifier, Keys key)
    {
        // increment the counter.
        _currentId = _currentId + 1;

        // register the hot key.
        if (!RegisterHotKey(_window.Handle, _currentId, (uint)modifier, (uint)key))
            throw new InvalidOperationException("Couldn’t register the hot key.");
    }

    /// <summary>
    /// A hot key has been pressed.
    /// </summary>
    public event EventHandler<KeyPressedEventArgs> KeyPressed;

    #region IDisposable Members

    public void Dispose()
    {
        // unregister all the registered hot keys.
        for (int i = _currentId; i > 0; i--)
        {
            UnregisterHotKey(_window.Handle, i);
        }

        // dispose the inner native window.
        _window.Dispose();
    }

    #endregion
}

/// <summary>
/// Event Args for the event that is fired after the hot key has been pressed.
/// </summary>
public class KeyPressedEventArgs : EventArgs
{
    private ModifierKeys _modifier;
    private Keys _key;

    internal KeyPressedEventArgs(ModifierKeys modifier, Keys key)
    {
        _modifier = modifier;
        _key = key;
    }

    public ModifierKeys Modifier
    {
        get { return _modifier; }
    }

    public Keys Key
    {
        get { return _key; }
    }
}

/// <summary>
/// The enumeration of possible modifiers.
/// </summary>
[Flags]
public enum ModifierKeys : uint
{
    Alt = 1,
    Control = 2,
    Shift = 4,
    Win = 8
}

to use (i had to edit the modifier keys to cast them (modifier)1 (modifier)2 etc

public partial  class Form1 : Form
{
    KeyboardHook hook = new KeyboardHook();

    public Form1()
    {
        InitializeComponent();

        // register the event that is fired after the key press.
        hook.KeyPressed +=
            new EventHandler<KeyPressedEventArgs>(hook_KeyPressed);
        // register the control + alt + F12 combination as hot key.
        hook.RegisterHotKey(ModifierKeys.Control | ModifierKeys.Alt,
            Keys.F12);
    }

    void hook_KeyPressed(object sender, KeyPressedEventArgs e)
    {
        // show the keys pressed in a label.
        label1.Text = e.Modifier.ToString() + " + " + e.Key.ToString();
    }
}

I took the answer from AaronLS and rewrote it a bit for a simple one-liner registration.

The Registration:

GlobalHotKey.RegisterHotKey("Alt + Shift + S", () => DoSomething());

The Class:

using System;
using System.Collections.Generic;
using System.Runtime.InteropServices;
using System.Windows.Input;

public class GlobalHotKey : IDisposable
{
    /// <summary>
    /// Registers a global hotkey
    /// </summary>
    /// <param name="aKeyGesture">e.g. Alt + Shift + Control + Win + S</param>
    /// <param name="aAction">Action to be called when hotkey is pressed</param>
    /// <returns>true, if registration succeeded, otherwise false</returns>
    public static bool RegisterHotKey(string aKeyGestureString, Action aAction)
    {
        var c = new KeyGestureConverter();
        KeyGesture aKeyGesture = (KeyGesture)c.ConvertFrom(aKeyGestureString);
        return RegisterHotKey(aKeyGesture.Modifiers, aKeyGesture.Key, aAction);
    }

    public static bool RegisterHotKey(ModifierKeys aModifier, Key aKey, Action aAction)
    {
        if(aModifier == ModifierKeys.None)
        {
            throw new ArgumentException("Modifier must not be ModifierKeys.None");
        }
        if (aAction is null)
        {
            throw new ArgumentNullException(nameof(aAction));
        }

        System.Windows.Forms.Keys aVirtualKeyCode = (System.Windows.Forms.Keys)KeyInterop.VirtualKeyFromKey(aKey);
        currentID = currentID + 1;
        bool aRegistered = RegisterHotKey(window.Handle, currentID,
                                    (uint)aModifier | MOD_NOREPEAT,
                                    (uint)aVirtualKeyCode);

        if(aRegistered)
        {
            registeredHotKeys.Add(new HotKeyWithAction(aModifier, aKey, aAction));
        }
        return aRegistered;
    }

    public void Dispose()
    {
        // unregister all the registered hot keys.
        for (int i = currentID; i > 0; i--)
        {
            UnregisterHotKey(window.Handle, i);
        }

        // dispose the inner native window.
        window.Dispose();
    }

    static GlobalHotKey()
    {
        window.KeyPressed += (s, e) =>
        {
            registeredHotKeys.ForEach(x =>
            {
                if (e.Modifier == x.Modifier && e.Key == x.Key)
                {
                    x.Action();
                }
            });
        };
    }

    private static readonly InvisibleWindowForMessages window = new InvisibleWindowForMessages();
    private static int currentID;
    private static uint MOD_NOREPEAT = 0x4000;
    private static List<HotKeyWithAction> registeredHotKeys = new List<HotKeyWithAction>();

    private class HotKeyWithAction
    {

        public HotKeyWithAction(ModifierKeys modifier, Key key, Action action)
        {
            Modifier = modifier;
            Key = key;
            Action = action;
        }

        public ModifierKeys Modifier { get; }
        public Key Key { get; }
        public Action Action { get; }
    }

    // Registers a hot key with Windows.
    [DllImport("user32.dll")]
    private static extern bool RegisterHotKey(IntPtr hWnd, int id, uint fsModifiers, uint vk);
    // Unregisters the hot key with Windows.
    [DllImport("user32.dll")]
    private static extern bool UnregisterHotKey(IntPtr hWnd, int id);

    private class InvisibleWindowForMessages : System.Windows.Forms.NativeWindow, IDisposable
    {
        public InvisibleWindowForMessages()
        {
            CreateHandle(new System.Windows.Forms.CreateParams());
        }

        private static int WM_HOTKEY = 0x0312;
        protected override void WndProc(ref System.Windows.Forms.Message m)
        {
            base.WndProc(ref m);

            if (m.Msg == WM_HOTKEY)
            {
                var aWPFKey = KeyInterop.KeyFromVirtualKey(((int)m.LParam >> 16) & 0xFFFF);
                ModifierKeys modifier = (ModifierKeys)((int)m.LParam & 0xFFFF);
                if (KeyPressed != null)
                {
                    KeyPressed(this, new HotKeyPressedEventArgs(modifier, aWPFKey));
                }
            }
        }

        public class HotKeyPressedEventArgs : EventArgs
        {
            private ModifierKeys _modifier;
            private Key _key;

            internal HotKeyPressedEventArgs(ModifierKeys modifier, Key key)
            {
                _modifier = modifier;
                _key = key;
            }

            public ModifierKeys Modifier
            {
                get { return _modifier; }
            }

            public Key Key
            {
                get { return _key; }
            }
        }


        public event EventHandler<HotKeyPressedEventArgs> KeyPressed;

        #region IDisposable Members

        public void Dispose()
        {
            this.DestroyHandle();
        }

        #endregion
    }
}

Here is a working [tag:vb.net] port of original answer:

###KeyboardHook.vb

Imports System.Runtime.InteropServices

Public NotInheritable Class KeyboardHook
	Implements IDisposable

	' Registers a hot key with Windows.
	<DllImport("user32.dll")> _
	Private Shared Function RegisterHotKey(hWnd As IntPtr, id As Integer, fsModifiers As UInteger, vk As UInteger) As Boolean
	End Function

	' Unregisters the hot key with Windows.
	<DllImport("user32.dll")> _
	Private Shared Function UnregisterHotKey(hWnd As IntPtr, id As Integer) As Boolean
	End Function

	''' <summary>
	''' Represents the window that is used internally to get the messages.
	''' </summary>
	Private Class Window
		Inherits NativeWindow
		Implements IDisposable
		Private Shared WM_HOTKEY As Integer = &H312

		Public Sub New()
			' create the handle for the window.
			Me.CreateHandle(New CreateParams())
		End Sub

		Public Event KeyPressed As EventHandler(Of KeyPressedEventArgs)

		''' <summary>
		''' Overridden to get the notifications.
		''' </summary>
		''' <param name="m"></param>
		Protected Overrides Sub WndProc(ByRef m As Message)
			MyBase.WndProc(m)

			' check if we got a hot key pressed.
			If m.Msg = WM_HOTKEY Then
				' get the keys.
				Dim key As Keys = DirectCast((CInt(m.LParam) >> 16) And &HFFFF, Keys)
				Dim modifier As ModifierKeys = DirectCast(CUInt(CInt(m.LParam) And &HFFFF), ModifierKeys)

				' invoke the event to notify the parent.
				RaiseEvent KeyPressed(Me, New KeyPressedEventArgs(modifier, key))
			End If
		End Sub

#Region " IDisposable Members"

		Public Sub Dispose() Implements IDisposable.Dispose
			Me.DestroyHandle()
		End Sub

#End Region
	End Class

	Private _window As New Window()
	Private _currentId As Integer

	Public Sub New()
		' register the event of the inner native window.
		AddHandler _window.KeyPressed, Sub(sender As Object, args As KeyPressedEventArgs)
										   RaiseEvent KeyPressed(Me, args)
									   End Sub
	End Sub

	''' <summary>
	''' Registers a hot key in the system.
	''' </summary>
	''' <param name="modifier">The modifiers that are associated with the hot key.</param>
	''' <param name="key">The key itself that is associated with the hot key.</param>
	Public Sub RegisterHotKey(modifier As ModifierKeys, key As Keys)
		' increment the counter.
		_currentId = _currentId + 1

		' register the hot key.
		If Not RegisterHotKey(_window.Handle, _currentId, DirectCast(modifier, UInteger), CUInt(key)) Then
			'Throw New InvalidOperationException("Couldn’t register the hot key.")
			'or use MsgBox("Couldn’t register the hot key.")
		End If
	End Sub

	''' <summary>
	''' A hot key has been pressed.
	''' </summary>
	Public Event KeyPressed As EventHandler(Of KeyPressedEventArgs)

#Region " IDisposable Members"

	Public Sub Dispose() Implements IDisposable.Dispose
		' unregister all the registered hot keys.
		Dim i As Integer = _currentId
		While i > 0
			UnregisterHotKey(_window.Handle, i)
			System.Math.Max(System.Threading.Interlocked.Decrement(i), i + 1)
		End While

		' dispose the inner native window.
		_window.Dispose()
	End Sub

#End Region
End Class

''' <summary>
''' Event Args for the event that is fired after the hot key has been pressed.
''' </summary>
Public Class KeyPressedEventArgs
	Inherits EventArgs
	Private _modifier As ModifierKeys
	Private _key As Keys

	Friend Sub New(modifier As ModifierKeys, key As Keys)
		_modifier = modifier
		_key = key
	End Sub

	Public ReadOnly Property Modifier() As ModifierKeys
		Get
			Return _modifier
		End Get
	End Property

	Public ReadOnly Property Key() As Keys
		Get
			Return _key
		End Get
	End Property
End Class

''' <summary>
''' The enumeration of possible modifiers.
''' </summary>
<Flags> _
Public Enum ModifierKeys As UInteger
	Alt = 1
	Control = 2
	Shift = 4
	Win = 8
End Enum

###Form1.vb Tasks:

1. Replace 2 instances of Application1 below with name of your application (it can be seen as root of tree in Visual Studio Solution Explorer window).
2. Add call to AddGlobalHotkeySupport() into initialization stage of your application.
3. Add call to RemoveGlobalHotkeySupport() into finalization stage of your application.

Code:

Public Sub AddGlobalHotkeySupport()  'TODO: call this at initialization of the application

    ' register the event that is fired after the key press.
    AddHandler hook.KeyPressed, AddressOf hook_KeyPressed

    ' register the control + alt + F12 combination as hot key.
    hook.RegisterHotKey(Application1.ModifierKeys.Control Or Application1.ModifierKeys.Alt, Keys.F12)

End Sub

Public Sub RemoveGlobalHotkeySupport()  'TODO: call this at finalization of the application
    ' unregister all registered hot keys.
    hook.Dispose()
End Sub

Private Sub hook_KeyPressed(sender As Object, e As KeyPressedEventArgs)
    ' show the keys pressed in a label.
    MsgBox(e.Modifier.ToString() + " + " + e.Key.ToString())
End Sub