Scroll a RichTextBox

4
votes

I would like to control a RichTextBox scrolling but can't find any method to perform this in the control.

The reason to do this is that I want the mouse wheel scroll to be effective when the mouse cursor in over the RichTextBox control (it has no active focus : mouse wheel event is handled by the form).

Any help is appreciated!

1
c#winformsscrollrichtextbox
Side note: A Windows application which does this system-wide is "KatMouse". I sadly don't know how to do it on your own in your program. – Ray
possible duplicate of Detecting mousewheel over non-focused window? – JMK
You could set the RichTextBox as selected control when hovering with mouse over it. – Max
The duplicate question leads to a link. I prefer King King answer giving a solution right away. – Martin Delille

1 Answers

2
votes

It's a little simple with win32. Here you are:

//must add using System.Reflection
public partial class Form1 : Form, IMessageFilter 
{
    bool hovered;
    MethodInfo wndProc;

    public Form1() 
    {
       InitializeComponent();
       Application.AddMessageFilter(this);
       richTextBox1.MouseEnter += (s, e) => { hovered = true; };
       richTextBox1.MouseLeave += (s, e) => { hovered = false; };
       wndProc = typeof(Control).GetMethod("WndProc", BindingFlags.NonPublic | 
                                                      BindingFlags.Instance);
    }

    public bool PreFilterMessage(ref Message m) 
    {
        if (m.Msg == 0x20a && hovered) //WM_MOUSEWHEEL = 0x20a
        {
           Message msg = Message.Create(richTextBox1.Handle, m.Msg, m.WParam, m.LParam);
           wndProc.Invoke(richTextBox1, new object[] { msg });
        }
        return false;
    }
}

NOTE: I use an IMessageFilter to catch the WM_MOUSEWHEEL message at the application-level. I also use Reflection to invoke the protected method WndProc to process the message WM_MOUSEWHEEL, you can always use a SendMessage win32 function to send the WM_MOUSEWHEEL to richTextBox1 instead, but it requires a declaration import here. It's up to you.