KeyboardHook

A hook is a mechanism by which an application can intercept events, such as messages, mouse actions, and keystrokes. A function that intercepts a particular type of event is known as a hook procedure. A hook procedure can act on each event it receives, and then modify or discard the event.

KeyboardHook enables you to monitor keyboard input events about to be posted in a thread input queue.

Use this component

If you have not already added it to your project, install the package from NuGet:

Install-Package NetEx.Hooks

Use the Install method to install the keyboard hook. Then subscribe to the events you wish to be notified of, such as KeyDown or KeyUp.

Note

The hook procedure should process a message as quickly as possible, and may be be skipped or removed if it is deemed to have timed out.

See the Install method for more information.

Example

The following example uses the Windows Forms Button control's Click event handler to install and uninstall the KeyboardHook. When the hook is installed, every press of the spacebar will increment the count Label.

using NetEx.Hooks;
using System;
using System.Windows.Forms;

public class KeyboardHookForm : Form
{
    [STAThread]
    public static void Main()
    {
        Application.SetCompatibleTextRenderingDefault(false);
        Application.EnableVisualStyles();
        Application.Run(new KeyboardHookForm());
    }

    private Button selectButton;
    private Label spacebarCountLabel;
    private int spacebarCount;
    private bool hooked;

    public KeyboardHookForm()
    {
        selectButton = new Button
        {
            Size = new Size(100, 20),
            Location = new Point(15, 15),
            Text = "Hook keyboard"
        };
        spacebarCountLabel = new Label
        {
            Size = new Size(150, 20),
            Location = new Point(15, 50),
            Text = "Spacebar count: 0"
        };
        selectButton.Click += new EventHandler(SelectButton_Click);
        ClientSize = new Size(330, 360);
        Controls.Add(selectButton);
        Controls.Add(spacebarCountLabel);

        KeyboardHook.KeyDown += e =>
        {
            if (e.KeyCode == NetEx.Hooks.Keys.Space)
            {
                spacebarCount++;
                spacebarCountLabel.Text = $"Spacebar count: {spacebarCount}";
            }
        };
    }
    private void SelectButton_Click(object sender, EventArgs e)
    {
        if (hooked)
        {
            if (KeyboardHook.TryUninstall())
            {
                selectButton.Text = "Hook keyboard";
                hooked = false;
            }
        }
        else
        {
            if (KeyboardHook.TryInstall())
            {
                selectButton.Text = "Unhook keyboard";
                hooked = true;
            }
        }
    }
}

Applies to

Product	Versions
.NET Framework	2.0, 3.0, 3.5, 4.0, 4.5, 4.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8, 4.8.1
Windows Desktop	5, 6, 7, 8, 9

See Also

Hooks Overview

LowLevelKeyboardProc function