subclassing NSCell - [self objectValue] with drawInteriorWithFrame:inView: returns strange results

Question

I have an NSTableView in my main window NIB file that uses a dynamically created datasource - that is, the array of dictionary's is created dynamically when required - in one of my classes. So it is not bound by any controllers in IB.

The tableview has 2 columns that have subclassed dataCell's set.

NSTableColumn *detailsColumn = [[tableView tableColumns] objectAtIndex:0];
imageColumnCell *fileDetails = [[[imageColumnCell alloc] init] autorelease];
[detailsColumn setDataCell:fileDetails];
[fileDetails setNumberOfUploads:numberOfFiles];

NSTableColumn *cancelColumn = [[tableView tableColumns] objectAtIndex:1];
cancelButtonCell *cancelCell = [[[cancelButtonCell alloc] init] autorelease];
[cancelColumn setDataCell:cancelCell];

In the <NSTableViewDataSource> file, numberOfRowsInTableView: is set to the correct count of the dynamically created array, and GDB logs it correctly when the table is drawn.

Now the problem comes in. For hypothetic reasons, let's say the array count for the datasource is 1

In both of the subclassed NSCell's I have overwritten the drawInteriorWithFrame:inView: method to handle all the drawing (images, text, buttons etc) inside the table cells. The NSDictionary for each column contains a string (column 1), and an object reference for (column 2).

Based on the example of 1 object in the datasource, if in drawInteriorWithFrame:inView: I were to write the following (in column 2):

NSLog(@"drawInteriorWithFrame: in cancelButtonCell - %@", [self objectValue]);

The expected result (without clicking on the table or scrolling etc) in GDB should be 1 instances of this:

[0000:000] drawInteriorWithFrame: in cancelButtonCell - <object: 0x123456>

And if I were to click or scroll in the table, then it should return the same values for each action within the tableview. However, on first load I get something like this:

[0000:000] drawInteriorWithFrame: in cancelButtonCell - <object: 0x123af06>
[0000:000] drawInteriorWithFrame: in cancelButtonCell - <object: 0x12b3236>

If there are 2 results, then I get 3 log items, and other times 4. In most cases, the method is called 1 more time than it should be.

The second problem, that has only just recently cropped up, is that if you notice the object ID's above, you will see that they are different. If I add 1 item to the datasource, when I call [self objectValue], if the table is redrawn, the object ID's should be the same, as it is a reference - ie. the object is already -alloc'd in the previous class, and I am merely sending the object reference.

I hope this makes sense, but I have been beating my head for the last day trying to see if I am mistakenly duplicating anything anywhere and cannot find any problems. If you need more code let me know. I have tried Google too and have only got reference to this:

http://forum.soft32.com/mac/NSPopUpButtonCell-view-refresh-ftopict46690.html

Thanks in advance.

- (id)tableView:(NSTableView *)tableView objectValueForTableColumn:(NSTableColumn *)tableColumn row:(NSInteger)row {

  NSString *columnIdentifier = [tableColumn identifier]; 
  NSDictionary *theDict = [fileSourceArray objectAtIndex:row];

  MyAppMethods *appMethods = [MyAppMethods alloc];
  if([appMethods getIsComplete:self])
    return nil;

  if([columnIdentifier isEqualToString:@"fileCancel"]){
    if([[theDict objectForKey:columnIdentifier] isKindOfClass:[ASIFormDataRequest class]]){
      ASIFormDataRequest *fileUploadRequest = [theDict objectForKey:columnIdentifier];
      NSLog(@"in tableView:objectValueForTableColumn:row %@", fileUploadRequest);
      return fileUploadRequest;
    }
  }
  return [theDict objectForKey:columnIdentifier];
}

Additional output for discussion below.

Output from GDB

** 1 file, 1 NSCell set and subclassed ** Here the request stays the same - (i.e. no copying)

[6619:903] <ASIFormDataRequest: 0x10ca9b0>
[6619:903] - (id)tableView:objectValueForTableColumn:row: /Users/byronrode/Desktop/Monika and Lubo/DSC_3379.jpg
[6619:903] imageColumnCell.m in - (void)drawInteriorWithFrame:inView: /Users/byronrode/Desktop/Monika and Lubo/DSC_3379.jpg
[6619:903] - (id)tableView:objectValueForTableColumn:row: <ASIFormDataRequest: 0x10ca9b0>
[6619:903] - (id)tableView:objectValueForTableColumn:row: /Users/byronrode/Desktop/Monika and Lubo/DSC_3379.jpg
[6619:903] imageColumnCell.m in - (void)drawInteriorWithFrame:inView: /Users/byronrode/Desktop/Monika and Lubo/DSC_3379.jpg
[6619:903] - (id)tableView:objectValueForTableColumn:row: <ASIFormDataRequest: 0x10ca9b0>

1 file, 2 NSCell's set and subclassed

Here the request changes in the subclass - (i.e. no copying)

[6652:903] <ASIFormDataRequest: 0x103b390>
[6652:903] - (id)tableView:objectValueForTableColumn:row: /Users/byronrode/Desktop/Monika and Lubo/DSC_3379.jpg
[6652:903] imageColumnCell.m in - (void)drawInteriorWithFrame:inView: /Users/byronrode/Desktop/Monika and Lubo/DSC_3379.jpg
[6652:903] - (id)tableView:objectValueForTableColumn:row: <ASIFormDataRequest: 0x103b390>
[6652:903] cancelButtonCell.m in - (void)drawInteriorWithFrame:inView: <ASIFormDataRequest: 0x1221b00>
[6652:903] - (id)tableView:objectValueForTableColumn:row: /Users/byronrode/Desktop/Monika and Lubo/DSC_3379.jpg
[6652:903] imageColumnCell.m in - (void)drawInteriorWithFrame:inView: /Users/byronrode/Desktop/Monika and Lubo/DSC_3379.jpg
[6652:903] - (id)tableView:objectValueForTableColumn:row: <ASIFormDataRequest: 0x103b390>
[6652:903] cancelButtonCell.m in - (void)drawInteriorWithFrame:inView: <ASIFormDataRequest: 0x1227100>

Is the table displaying incorrectly, or are you just concerned about the apparent extra call to `-drawInteriorWithFrame:`? Also, have you looked at the represented object _before_ you pass it to the cell? How does that compare to what the cell says its object value is? — jscs, Apr 19 '11 at 17:11
@josh-caswell - the table display's correctly (no extra data). In my class that creates the datasource, the actual object, the dictionary, and the array containing the dictionary all contain the same object id. In the DataSource, in `tableView:objectValueForTableColumn:row:` the object is still correctly referenced, but in my NSCell subclass the reference changes, and all the extra calls are different to the original reference. I also have noticed that `tableView:objectValueForTableColumn:row:` is being called 3 times for a 2 column table with one "row" in the datasource. — Byron Rode, Apr 19 '11 at 18:40
In testing further, I found the "extra calls" to be related to the number of columns, which was more obvious after not staring at it for so long, so that part makes sense. Where the problem seems to be now is if I remove the second dataCell subclass `cancelColumn` (above) then the referenced object is correctly identified. I have updated the question with my `- tableView:objectValueForTableColumn:row:` method. — Byron Rode, Apr 19 '11 at 18:57
Are both of your table columns using this same custom cell class? — jscs, Apr 19 '11 at 19:11
Nope. Each uses a separate cell class. It used to be one column, using one custom cell but there was a performance issue with mouse tracking so I split it off so that the tracking was related to the column that needed click tracking. — Byron Rode, Apr 19 '11 at 19:14
So you're only gettin the extra call from the `cancelButtonCell`, and _not_ the `imageColumnCell`? — jscs, Apr 19 '11 at 19:22
It's safe to say the "extra" call is actually just the necessary drawing for each cell. i.e. 1 row, 2 columns, means two `-draw...` calls. — Byron Rode, Apr 19 '11 at 19:53

jscs · Accepted Answer · 2011-08-24T20:02:17.620

0

I don't think there's anything to worry about if it's displaying correctly. A table view asks its table columns for "dummy" cells before finalizing their drawing; I suspect that is the cause of the extra -draw... call. Also, the cell copies its object value when setting, so that would obviously give it a new address.

In response to your posting of log messages:

I'm not 100% clear on when exactly these logs are being posted, and what they are displaying, but that looks like what I'd expect to see. In tableView:objectValueForTableColumn:row: you're printing the value that you have in your dictionary, which is the same as the original ASIFormDataRequest. In drawInteriorWithFrame:inView: you're printing the cell's objectValue, which is a copy of that original (i.e., a new object, with a different address in memory).

edited Aug 24 '11 at 20:02

answered Apr 19 '11 at 19:23

jscs

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That makes sense, but surely the copying would then be the same when using either one or 2 custom column cells. Except in this case the address is changed when using 2 custom cells. I have added more information to the question. Maybe it will make more sense now. – Byron Rode Apr 19 '11 at 19:46
It looks to me like these are AppKit implementation details that aren't affecting your program. I still say "Don't worry about it". In order to their jobs efficiently, the table view, table columns, and `NSCell` all do things behind the scenes that you may not expect. – jscs Apr 19 '11 at 20:24

subclassing NSCell - [self objectValue] with drawInteriorWithFrame:inView: returns strange results

Output from GDB

1 file, 2 NSCell's set and subclassed

1 Answers1