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GetScrollInfo and SetScrollInfo in RichTextBox

Posted on 2004-10-18
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Last Modified: 2008-01-09
Hello,

I'm trying to write a small JAVA text editor with basic real-time syntax highlighting.

I created a 'SyntaxBox' class and derived it from the RichTextBox control.
Inside the class I implemented a procedure 'Parse' which converts the text in the textbox to the Rich Text Format including the correct syntax color formatting.
I then copy the RTF text to the 'Rtf' property of the RichTextBox control and it shows me a nice and smooth highlighted syntax.

However, every time I update my rich text, the cursor runs to the start of the textbox.
I solved this by remembering the SelectionStart property and resetting it after the update.
BUT, I still have a problem with the scrollbar.

As soon as I start typing, the scrollbar jumps to another value.
I'm trying to read the scrollbar position using the 'GetScrollInfo' procedure in user32.dll (the GetScrollPos procedure doesn't seem to work).
This works great, however, I can't seem to set the scrollbar back to its previous value. (or to any value whatsoever, for that matter)
If I call SetScrollInfo(<params>) and immediately afterwards I call the GetScrollInfo procedure, it shows me the correct value.
However, the scroll position of the textbox is not updated...

So I have a few questions:

1.) am I using the right approach to syntax highlighting?
2.) how come the SetScrollInfo procedure doesn't update my textbox?

Here's some relevant code:

public void SetRTF(string text)
{
      ScrollInfoStruct s=new ScrollInfoStruct();

      s.fMask=SIF_POS; //only position
      s.cbSize=Marshal.SizeOf(s);

      if(GetScrollInfo(this.Handle,1,ref s)==0)
            MessageBox.Show("GetScrollInfo error: "+GetLastError().ToString());

      int st=this.SelectionStart;
      int sl=this.SelectionLength;

      this.Rtf=text;

      this.SelectionStart=st;
      this.SelectionLength=sl;

      if(SetScrollInfo(this.Handle,1,ref s,false)==0)
            MessageBox.Show("SetScrollInfo error: "+GetLastError().ToString());

      this.Refresh();
}

Thanks in advance...

Nicolas.
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Question by:The_LowRider
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by:Bob Learned
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Try the ScrollToCaret method of the RichTextBox.

Bob
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Author Comment

by:The_LowRider
Comment Utility
> Try the ScrollToCaret method of the RichTextBox.

Bob, thanks for the suggestion, however, it doesn't work.
Resetting the SelectionStart property already takes care of this.

Maybe I should be more specific about the 'scrollbar jumps' part.

If I scroll down to the bottom of the text and then place the cursor on the first visible line of the textbox, like in the top part of this screenshot:

http://users.pandora.be/bajaman/screenshot.gif

When I run my syntax highlighting procedure (simply by entering some text), the textbox scrolls upward, like in the bottom part of the screenshot.

thanks,

Nicolas.
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Accepted Solution

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Bob Learned earned 500 total points
Comment Utility
Oooh, right, you want exact position of scroll bars.

Have you seen this?

Scrolling Around with the RichTextBox Control
http://www.codeproject.com/vb/net/VbNetScrolling.asp?print=true

Bob
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LVL 96

Expert Comment

by:Bob Learned
Comment Utility
It is VB.NET, but might be convertible to C#.

Bob
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Author Comment

by:The_LowRider
Comment Utility
Yes! That PostMessageA procedure works great!

I stumbled upon that code in the beginning of my search but left it alone because it was VB.net and because it used those "really weird Windows messages" :)

Thanks, just what I needed!

Nicolas.
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