How can I find the state of NumLock, CapsLock and ScrollLock in .NET?

Question

How can I find the state of NumLock, CapsLock and ScrollLock keys in .NET?

Answer 1

Check State

To check state of CapsLock, NumLock and ScrollLock keys you can use Control.IsKeyLocked method:

var capsLockIsOn = Control.IsKeyLocked(Keys.CapsLock);

Actively Show The State in UI in status bar

Since the lock keys can be turn on or turn off when your application doesn't have focus handling keyboard events of the form is not enough to detect changes on the key lock state and you should also put your logic in some other places like activation event of your form or you need to register a global keyboard hook.

As a simple and reliable solution you can check their status in Application.Idle event. You must detach your idle event handler when your form closed.

public Form1()
{
    InitializeComponent();
    Application.Idle += Application_Idle;
}

void Application_Idle(object sender, EventArgs e)
{
    if (Control.IsKeyLocked(Keys.CapsLock))
        toolStripStatusLabel1.Text = "CapsLock is On";
    else
        toolStripStatusLabel1.Text = "";
}

protected override void OnFormClosed(FormClosedEventArgs e)
{
    Application.Idle -= Application_Idle;
    base.OnFormClosed(e);
}