Scrolling textboxes programmatically using WndProc messages.

Question

Hi,

I'm trying to scroll a textbox using the form's WndProc method. The code I've come up with so far, after scouring the internet, looks like this:

private void ScrollTextBox()
{
    scrollMessage = Message.Create(TabContents.Handle, 0x00B6, new IntPtr(0x0003), new IntPtr(0x0000));
    this.WndProc(ref scrollMessage);
}

where TabContents is a TextBox.

For some reason, nothing happens when i call this method. I'd like to know why. I realise that i can accomplish the same with the MoveToCaret method, but I'm curious why this is not working.

EDIT: As in the posted answer from Beaner, I wrote another method using SendMessage:

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

        private void ScrollTextBox2(int lines)
        {
            SendMessage(TabContents.Handle, 0x00B6, new IntPtr(0), new IntPtr(lines));
        }

This seems to work %100. I'm still curious why this.WndProc(ref message) doesn't work, given a message created with the same set of parameters.

Answer 1

This may be possible, but I have never tried it that way. I have used SendMessage to send a windows message directly to the textbox to cause scrolling.

private const int WM_VSCROLL = 0x115;
private const int SB_BOTTOM = 7;

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

// Scroll to the bottom, but don't move the caret position.
SendMessage(TabContents.Handle, WM_VSCROLL, (IntPtr) SB_BOTTOM, IntPtr.Zero);