How can I sync the scrolling of two multiline textboxes?

Question

How can I sync the scrolling of two multiline textboxes in C# (WinForms)?

When you scroll up/down a line in TextBox A, TextBox B should scroll up/down too. The same

Answer 1

Here is what finally helped me to fix synchronization of multiple textboxes using mouse wheel.

I based it on very helpful Hans example.

int WM_MOUSEWHEEL   = 0x20a; // or 522
int WM_VSCROLL      = 0x115; // or 277

protected override void WndProc(ref Message m)
{
        //Trap WM_VSCROLL and WM_MOUSEWHEEL message and pass to buddy
        if (Buddies != null)
        {

            if (m.Msg == WM_MOUSEWHEEL)  //mouse wheel 
            {

                if ((int)m.WParam < 0)  //mouse wheel scrolls down
                    SendMessage(this.Handle, (int)0x0115, new IntPtr(1), new IntPtr(0)); //WParam: 1- scroll down, 0- scroll up
                else if ((int)m.WParam > 0)
                    SendMessage(this.Handle, (int)0x0115, new IntPtr(0), new IntPtr(0));



                return; //prevent base.WndProc() from messing synchronization up 
            }
            else if (m.Msg == WM_VSCROLL)
            {
                foreach (Control ctr in Buddies)
                {
                    if (ctr != this && !scrolling && ctr != null && ctr.IsHandleCreated)
                    {
                        scrolling = true;
                        SendMessage(ctr.Handle, m.Msg, m.WParam, m.LParam);
                        scrolling = false;
                    }

                }

            }
        }

    //do the usual
    base.WndProc(ref m);
}