Question

I have a RichTextBox with ScrollBars set to None. According to MSDN

The DefWindowProc function propagates the message to the window’s
parent. There should be no internal forwarding of the message, since
DefWindowProc propagates it up the parent chain until it finds a
window that processes it.

I interpret this as, I should not need to hook into the message pump (IMessageFilter) and manually forward WM_MOUSEWHEEL events to the parent Form containing the richtextbox. When I am inside of RichTextBox and perform a mouse scroll, the Form does not scroll. Why not? How can I get the Form to scroll?

Keep in mind that scrollbars are set to none for RichTextBox and enabled for the Form. So why isn’t the form getting the scroll event?

public partial class Form4 : Form
{
    public Form4()
    {
        InitializeComponent();
        this.AutoScroll = true;
        richTextBox1.ScrollBars = RichTextBoxScrollBars.None;
    }
}

Answer 1

The form doesn’t scroll because the RichTextBox handles the WM_MOUSEWHEEL itself and doesn’t call DefWindowProc to forward it to its parent. Apparently that doesn’t change when disabling the scroll bars.

So you either need to implement an IMessageFilter or create a subclass of RichTextEdit that will forward the WM_MOUSEWHEEL as shown here:

public class NoScrollRichTextBox : RichTextBox
{
   const int WM_MOUSEWHEEL = 0x020A;

   protected override void WndProc(ref Message m)
   {
      // This will completely ignore the mouse wheel, which will disable zooming as well
      if (m.Msg != WM_MOUSEWHEEL)
         base.WndProc(ref m);
   }
}