Creating a System.Windows.Forms.TextBox that automatically selects text on focus (like a browser's URL bar)

FocusTextBox.cs

    public class FocusTextBox : System.Windows.Forms.TextBox
    {
        private bool _focussed;

        protected override void OnEnter(EventArgs e)
        {
            base.OnEnter(e);
            if (MouseButtons == MouseButtons.None)
            {
                SelectAll();
                _focussed = true;
            }
        }

        protected override void OnLeave(EventArgs e)
        {
            base.OnLeave(e);
            _focussed = false;
        }

        protected override void OnMouseUp(MouseEventArgs mevent)
        {
            base.OnMouseUp(mevent);
            if (!_focussed)
            {
                if (SelectionLength == 0)
                    SelectAll();
                _focussed = true;
            }
        }
    }