Re: NSArrayController and threading

FROM : Joe Chan
DATE : Wed Dec 22 22:27:25 2004

After some experiments I found the following interesting facts:

- In order for changes to occur, -willChangeValueForKey: is definitely
needed.
- For some reason -didChange:valuesAtindexes:forKey: doesn't work, but
-didChangeValueForKey: does.

My model objects roughly look like this:

@interface Record : NSObject
{
   NSMutableDictionary    *_data;
}
...
- (void)loadThumbnail; // called within the thread to load the image
- (NSImage*)thumbnail; // return some default image if not loaded yet
@end

@interface Document : NSDocument
{
   NSMutableArray    *_recordList;
}
- (NSMutableArray*)recordList;
- (void)startLoadFiles;
- (void)loadFiles;
- (void)fileLoaded: (NSIndexSet *) indexes;
@endif

Inside fileLoaded:, I have to do something like this:

- (void)fileLoaded: (NSIndexSet *) indexes
{
   Record    *rec = [_recordList objectAtIndex: [indexes firstIndex]];
   [rec willChangeValueForKey: @"thumbnail"];
   [rec didChangeValueForKey: @"thumbnail"];

/* This doesn't work
   [self willChange: NSKeyValueChangeReplacement valuesAtIndexes:indexes
forKey:@"thumbnail"];
   [self didChange:  NSKeyValueChangeReplacement valuesAtIndexes:indexes
forKey:@"thumbnail"];
*/
}

Which seems very strange to me. Is this a bug in the binding stuff, or
am I not understanding willChange:valuesAtIndexes:forKey: right?

On Dec 22, 2004, at 4:08 PM, John C. Randolph wrote:

>
> On Dec 22, 2004, at 6:29 AM, Joe Chan wrote:
>
>
>

>> This approach is much simpler than my initial guess. The loading of
>> thumbnail works, however, the table is not getting updated with the
>> thumbnails until I scroll. Unfortunately, because binding eliminated
>> almost all the glue code, it also makes it very hard to debug why
>> it's not getting updated. I thought that once the didChange: is
>> called, the NSArrayController will trigger an update on the
>> NSImageCell and should redraw itself.

>
> Hmm..  I wrote the code off the top of my head, and haven't tested it
> in an app. You might try sending -willChangeValueForKey: before
> -didChange:valuesAtIndexes:forKey:.
>
>
>
> -jcr
>

>>

>
>
>
> John C. Randolph <<email_removed>> (408) 974-8819
> Sr. Cocoa Software Engineer,
> Apple Worldwide Developer Relations
> http://developer.apple.com/cocoa/index.html
>
>
>

--
Joe Chan
Sun Microsystems, Inc.
Burlington, MA
Tel: (781) 442-0809