TextBoxSynchronizedScroll.cs

// http://stackoverflow.com/questions/3322741/synchronizing-multiline-textbox-positions-in-c/3779949#3779949

namespace Kingry.StackOverFlow.Question_3779949
{
    using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Text;
    using System.Windows.Forms;

    class TextBoxSynchronizedScroll : TextBox
    {
        public const int WM_VSCROLL = 0x115;

        List<TextBoxSynchronizedScroll> peers = new List<TextBoxSynchronizedScroll>();

        public void AddPeer(TextBoxSynchronizedScroll peer)
        {
            this.peers.Add(peer);
        }

        private void DirectWndProc(ref Message m)
        {
            base.WndProc(ref m);
        }

        protected override void WndProc(ref Message m)
        {
            if (m.Msg == WM_VSCROLL)
            {
                foreach (var peer in this.peers)
                {
                    var peerMessage = Message.Create(peer.Handle, m.Msg, m.WParam, m.LParam);
                    peer.DirectWndProc(ref peerMessage);
                }
            }

            base.WndProc(ref m);
        }
    }
}