Bloggy

I never thought that I would have as much trouble understanding bugs as I
just now had for a bug in JuK. First, a description of the bug is needed.

• It only happens when using the Inline Tag Editor to edit a tag.
• It only affects on Search Playlists (with another qualifier I’ll add
  later).
• It only happens when setting a tag value to a value alread present in any
  of the other songs.

This bug keeps the Search Playlists that search on the tag being edited
from being refreshed. So if you were to edit a song and change the tag so
that it now belongs in one of those Search Playlists, it wouldn’t show up
there until you somehow managed to force it to refresh (such as by adding an
item).

Many, many kdDebug() statements later, I discovered that the
bug doesn’t affect newly created Search Playlists, only ones loaded from disk.
Turns out that what was happening is that Search Playlists are created with a
so-called Playlist Observer. Whenever a playlist changes, it can call
PlaylistInterface::update(), and any class which is observing it
will be notified. It’s a very elegant design.

The problem is that when loaded from disk, the Search Playlists have
“forgotten” what Playlists they were observing. Scott had gotten around this
problem by connecting to a signal that the main playlist class
(CollectionList) emits when it has changed. Since at this point in time this
is also the only playlist that is ever observed, the solution worked well
enough.

So it turns out that my bug was in a completely different class
(CollectionList), which didn’t always emit the changed signal when the
collection has changed (to be specific, it didn’t track the individual items
themselves changing, just the addition or removal of them, and the addition of
new tags, which was why adding an existing tag failed to refresh the
list).

Whew! :-) Now that I understand this code much better, it should be easier
for me to fix the bugs in automatically updating dynamic playlists, and get my
retag-on-drag-and-drop code in CVS.

Posted by mpyne under KDE & Programming | No Comments »