[BUG][FIX] Scrolling in MVC ([er][et][sm] [approved])

Doug Way dway at mailcan.com
Sat May 22 04:08:29 UTC 2004

Fixes the specified scrolling problem in MVC.

There is a little bit of risk with this, since Morphic uses this method 
too.  But the fix itself looks reasonable.

- Doug

On Thursday, April 29, 2004, at 08:10 AM, Boris Gaertner wrote:

> Hello,
> earlier this day I posted a mail with a list of bugs that I think 
> should
> be fixed before we close 3.7. For one of these bugs, no fix has
> been proposed so far.
> I am therefore really happy to offer a problem analysis and a fix for
> the bug that is registered under BFAV archive ID 14350,
> posted at Nov 26, 2003.
> For quite a time, I was only able to hack around a problem that I did
> not understand, but now I think I have found was goes wrong.
> Here is the bug description again:
> ( from the cited bug report)
>> In an MVC project, open a file list and select a text file.
>> Place the cursor into the text view (at the beginning of the text)
>> and scroll down with the down arrow.
>> When you reach the end of the text, you will get a notifier
>> with the message as soon as you release the 'arrow down' key:
>> MessageNotUnderstood: UndefinedObject>>first
>> This comes from
>> ParagraphEditor>>sameColumn:newLine:forward:,
> And here is an analysis of the bug:
> In method
> ParagraphEditor>>sameColumn: start newLine: lineBlock forward: 
> isForward
> we read:
>  targetLineNumber _ ((lineBlock value: currentLineNumber) max: 1)
>                                 min: lines size.
> where lines is a temporary variable of the method. Under some
> circumstances, the method  fetches the lines from the paragraph
> that is edited. (The paragraph is an instance of Paragraph in
> MVC and an instance of NewParagraph in Morphic)
> Under different circumstances, sameColumn:lineBlock:forward:
> computes an array of lines (this is done by ParagraphEditor>>lines).
> In NewParagraph, 'lines' is used under an exact fit policy:
> For a paragraph that is composed to be displayed in  n
> lines, the size of the array is  n .
> In a Paragraph, 'lines' is an array of TextLineIntervals.
> In Paragraph, the array 'lines' is used under a "keep
> additional space" policy and the correct number of lines
> is stored in instance variable 'lastLine' and can be
> accessed with the method Paragraph>>numberOfLines
> When sameColumn:lineBlock:forward:  computes an array
> of lines, it can use 'lines size' to obtain the number of lines, but
> when it uses the lines from the paragraph, it has to use
> 'paragraph numberOfLines' to obtain the number of lines.
> Solution:
> To handle both cases, I use an additional instance variable
> to keep the number of lines.
> I would be glad to see this fix in the final 3.7 (if that is
> still possible), so can some fellow with an interest in
> MVC please review my proposal?
> Thank you a lot!
> Boris<MVCCursorDownFix.1.cs>

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