HotkeyTextBox

HotkeyTextBox.cs

public sealed class HotkeyTextBox : TextBox
{
    public Keys Modifier { get; private set; }
    public Keys Key { get; private set; }

    public HotkeyTextBox()
    {
        Text = "None";
        GotFocus += delegate { NativeMethods.HideCaret(Handle); };
    }

    protected override void OnKeyPress(KeyPressEventArgs e)
    {
        // do not send the key data to the OS for default processing.
        // we will render the key data ourselves.
        //
        e.Handled = true;
    }

    protected override void OnKeyDown(KeyEventArgs e)
    {
        if (e.KeyCode == Keys.Back)
        {
            ClearHotkeyText();
            return;
        }

        Modifier = e.Modifiers;
        Key = e.KeyCode;
        RenderHotkeyText();
    }

    private void ClearHotkeyText()
    {
        Modifier = Keys.None;
        Key = Keys.None;
        Text = "None";
    }

    private void RenderHotkeyText()
    {
        EnsureKeyIsNotModifier();

        if (Modifier != Keys.None)
        {
            Text = Modifier.ToString().Replace(", ", " + ");
            
            if (Key != Keys.None)
            {
                Text += " + " + Key;
            }
            return;
        }

        Text = Key.ToString();
    }

    private void EnsureKeyIsNotModifier()
    {
        if (Key == Keys.ControlKey || 
            Key == Keys.Menu || 
            Key == Keys.ShiftKey || 
            Key == Keys.LWin || 
            Key == Keys.RWin)
        {
            Key = Keys.None;
        }
    }
}

internal static class NativeMethods
{
    [DllImport("user32.dll")]
    public static extern bool HideCaret(IntPtr controlHandle);
}