C#: Synchronize Scroll Position of two RichTextBoxes?

Question

In my application's form, I have two RichTextBox objects. They will both always have the same number of lines of text. I would like to "synchronize" the vertical scrolling between these two, so that when the user changes the vertical scroll position on one, the other scrolls the same amount. How might I go about doing this?

Answer 1

Thanks Jay for your answer; after some more searching I also found the method described here. I'll outline it below for anyone else interested.

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First, declare the following enums:

public enum ScrollBarType : uint {
   SbHorz = 0,
   SbVert = 1,
   SbCtl = 2,
   SbBoth = 3
 }

public enum Message : uint {
   WM_VSCROLL = 0x0115
}

public enum ScrollBarCommands : uint {
   SB_THUMBPOSITION = 4
}

Next, add external references to GetScrollPos and SendMessage.

[DllImport( "User32.dll" )]
public extern static int GetScrollPos( IntPtr hWnd, int nBar );

[DllImport( "User32.dll" )]
public extern static int SendMessage( IntPtr hWnd, uint msg, IntPtr wParam, IntPtr lParam );

Finally, add an event handler for the VScroll event of the appropriate RichTextBox:

private void myRichTextBox1_VScroll( object sender, EventArgs e )
{
   int nPos = GetScrollPos( richTextBox1.Handle, (int)ScrollBarType.SbVert );
   nPos <<= 16;
   uint wParam = (uint)ScrollBarCommands.SB_THUMBPOSITION | (uint)nPos;
   SendMessage( richTextBox2.Handle, (int)Message.WM_VSCROLL, new IntPtr( wParam ), new IntPtr( 0 ) );
}

In this case, richTextBox2's vertical scroll position will be synchronized with richTextBox1.