SystemTrayMenu/Helpers/MessageFilter.cs

using System.Drawing;
using System.Windows.Forms;

namespace SystemTrayMenu.Helper
{
    public delegate void EventHandler();

    internal class MessageFilter : IMessageFilter
    {
        private const int WM_MOUSELEAVE = 0x02A3;
        private const int WM_MOUSEMOVE = 0x0200;
        private const int WM_NCMOUSEMOVE = 0x00A0;
        public event EventHandler MouseLeave;
        public event EventHandler MouseMove;
        public event EventHandler ScrollBarMouseMove;

        private Point cursorPosition = new Point();
        private bool messageFilterAdded = false;

        public bool PreFilterMessage(ref Message message)
        {
            if (message.Msg == WM_MOUSELEAVE)
            {
                MouseLeave?.Invoke();
            }
            else if (message.Msg == WM_MOUSEMOVE)
            {
                Point newCursorPosition = Cursor.Position;
                if (!newCursorPosition.Equals(cursorPosition))
                {
                    MouseMove?.Invoke();
                }
                cursorPosition = newCursorPosition;
            }
            else if (message.Msg == WM_NCMOUSEMOVE)
            {
                ScrollBarMouseMove?.Invoke();
            }
            return false;
        }

        internal void StartListening()
        {
            if (!messageFilterAdded)
            {
                Application.AddMessageFilter(this);
                messageFilterAdded = true;
            }
        }

        internal void StopListening()
        {
            if (messageFilterAdded)
            {
                Application.RemoveMessageFilter(this);
                messageFilterAdded = false;
            }
        }
    }
}