How do you prevent a RichTextBox from refreshing its display?

Question

I have a RichTextBox where I need to update the Text property frequently, but when I do so the RichTextBox \"blinks\" annoyingly as it refreshes all throughout a method call

Answer 1

Here is complete and working example:

    private const int WM_USER = 0x0400;
    private const int EM_SETEVENTMASK = (WM_USER + 69);
    private const int WM_SETREDRAW = 0x0b;
    private IntPtr OldEventMask;       

    [DllImport("user32.dll", CharSet=CharSet.Auto)]
    private static extern IntPtr SendMessage(IntPtr hWnd, int msg, IntPtr wParam, IntPtr lParam);

    public void BeginUpdate()
    {
        SendMessage(this.Handle, WM_SETREDRAW, IntPtr.Zero, IntPtr.Zero);
        OldEventMask = (IntPtr)SendMessage(this.Handle, EM_SETEVENTMASK, IntPtr.Zero, IntPtr.Zero);
    }       

    public void EndUpdate()
    {
        SendMessage(this.Handle, WM_SETREDRAW, (IntPtr)1, IntPtr.Zero);
        SendMessage(this.Handle, EM_SETEVENTMASK, IntPtr.Zero, OldEventMask);
    }

Answer 2

I would suggest looking at LockWindowUpdate

[DllImport("user32.dll", EntryPoint="LockWindowUpdate", SetLastError=true,
ExactSpelling=true, CharSet=CharSet.Auto,
CallingConvention=CallingConvention.StdCall)]

Answer 3

Could you just store the Text into a string, do your manipulations on the string, and at the end of the method, store it back into the Text property?

Answer 4

Try this out:

myRichTextBox.SuspendLayout();
DoStuff();
myRichTextBox.ResumeLayout();

Answer 5

I asked the original question, and the answer that worked best for me was BoltBait's use of SendMessage() with WM_SETREDRAW. It seems to have fewer side effects than the use of the WndProc method, and in my application performs twice as fast as LockWindowUpdate.

Within my extended RichTextBox class, I just added these two methods, and I call them whenever I need to stop restart repainting while I'm doing some processing. If I were wanting to do this from outside of the RichTextBox class, I think it would work by just replacing "this" with the reference to your RichTextBox instance.

    private void StopRepaint()
    {
        // Stop redrawing:
        SendMessage(this.Handle, WM_SETREDRAW, 0, IntPtr.Zero);
        // Stop sending of events:
        eventMask = SendMessage(this.Handle, EM_GETEVENTMASK, 0, IntPtr.Zero);
    }

    private void StartRepaint()
    {
        // turn on events
        SendMessage(this.Handle, EM_SETEVENTMASK, 0, eventMask);
        // turn on redrawing
        SendMessage(this.Handle, WM_SETREDRAW, 1, IntPtr.Zero);
        // this forces a repaint, which for some reason is necessary in some cases.
        this.Invalidate();
    }

Answer 6

Found here: http://bytes.com/forum/thread276845.html

I ended up sending a WM_SETREDRAW via SendMessage to disable then reenable followed by an Invalidate() after I finished updating. That seemed to work.

I've never tried this method. I have written an application with a RTB that has syntax highlighting and used the following in the RTB class:

protected override void WndProc(ref Message m)
{
    if (m.Msg == paint)
    {
        if (!highlighting)
        {
            base.WndProc(ref m); // if we decided to paint this control, just call the RichTextBox WndProc
        }
        else
        {
            m.Result = IntPtr.Zero; // not painting, must set this to IntPtr.Zero if not painting otherwise serious problems.
        }
    }
    else
    {
        base.WndProc(ref m); // message other than paint, just do what you normally do.
    }
}

Hope this helps.