iOS Strange problem with cellForRowAtIndexPath:

[RonC]

This one is a little weird - I can't seem to find anyone else who has had a similar problem so I'm coming here where answers abound!

What I want to do is "blink" the selection status of a cell - toggle it between selected and deselected. I have the indexPath for this cell (for now, let's just call that (0,0), but it seems to fail independent of the value).

Here's the code I'm using:

-(void)toggleRowSelection:(NSIndexPath *)indexPath
{
    UITableViewCell *cell = [self.tableView cellForRowAtIndexPath:indexPath];
    if (cell) {
        NSLog(@"[%@] cell=%@ selected=%@", whoAmI(self, _cmd), cell, cell.isSelected);
        [cell setSelected:!cell.isSelected animated:YES];
    }
}
        
#define BLINK_ANIMATION_DELAY   (0.33)

-(void)scanSuccessForAProw:(int)apRow
{
    [self.tableView reloadData];
    // Animate the checkmark
    [self animateScanCheckmark:self.bigCheckmarkView
                     withSound:self.goodBeepSoundID];
    if (apRow >= 0) {
        NSIndexPath *indexPath = [NSIndexPath indexPathForRow:apRow
                                                    inSection:0];
        // Make sure row is visible
        [self.tableView selectRowAtIndexPath:indexPath
                                    animated:YES
                              scrollPosition:UITableViewScrollPositionNone];
        
        NSLog(@"[%@] indexPath=%@ (%@ = %d)", whoAmI(self, _cmd),
              indexPath, [self.tableView indexPathForSelectedRow],
              [indexPath isEqual:[self.tableView indexPathForSelectedRow]]);
        // animate the row
//        [self toggleRowSelection:indexPath];                    // ON
        [self performSelector:@selector(toggleRowSelection:)
                   withObject:indexPath
                   afterDelay:BLINK_ANIMATION_DELAY];           // OFF
        [self performSelector:@selector(toggleRowSelection:)
                   withObject:indexPath
                   afterDelay:2*BLINK_ANIMATION_DELAY];         // ON
        [self performSelector:@selector(toggleRowSelection:)
                   withObject:indexPath
                   afterDelay:3*BLINK_ANIMATION_DELAY];         // OFF
        [self animateTableView:TABLE_VIEW_ANIMATION_DURATION_SUCCESS];
    }
}

The code crashes at the NSLog statement in toggleRowSelection: with EXC_BAD_ACCESS. Apparently the value in cell is bad, so I started digging into that in the debugger. Here's my debugger log:

2011-09-19 13:38:03.713 Zone Installer[14360:207] [InventoryViewController_iPhone.scanSuccessForAProw:] indexPath=<NSIndexPath 0x5c555e0> 2 indexes [0, 0] (<NSIndexPath 0x5c555e0> 2 indexes [0, 0] = 1)
Current language:  auto; currently objective-c++
Single stepping until exit from function objc_msgSend, 
which has no line number information.
(gdb) p (int)[indexPath retainCount]
$1 = 5
(gdb) po tableView
No symbol "tableView" in current context.
(gdb) po [self tableView]
<UITableView: 0x6849400; frame = (20 44; 280 223); clipsToBounds = YES; alpha = 0; autoresize = W+H; animations = { opacity=<CABasicAnimation: 0x5c644c0>; }; layer = <CALayer: 0x709d610>; contentOffset: {0, 0}>
(gdb) po [[self tableView] cellForRowAtIndexPath:indexPath]
<HaveNeedTableViewCell: 0x5c76720; baseClass = UITableViewCell; frame = (0 0; 280 44); autoresize = W; layer = <CALayer: 0x5c73740>>
(gdb) p (int) [[[self tableView] cellForRowAtIndexPath:indexPath] retainCount]
$2 = 2
(gdb) po [[self tableView] visibleCells]
<__NSArrayM 0x5c60660>(
<HaveNeedTableViewCell: 0x5c76720; baseClass = UITableViewCell; frame = (0 0; 280 44); autoresize = W; layer = <CALayer: 0x5c73740>>,
<HaveNeedTableViewCell: 0x5c79770; baseClass = UITableViewCell; frame = (0 44; 280 44); autoresize = W; layer = <CALayer: 0x5c799a0>>,
<HaveNeedTableViewCell: 0x5c7ca00; baseClass = UITableViewCell; frame = (0 88; 280 44); autoresize = W; layer = <CALayer: 0x5c7cc30>>,
<HaveNeedTableViewCell: 0x5c7fb50; baseClass = UITableViewCell; frame = (0 132; 280 44); autoresize = W; layer = <CALayer: 0x5c7fd80>>,
<HaveNeedTableViewCell: 0x5c82c50; baseClass = UITableViewCell; frame = (0 176; 280 44); autoresize = W; layer = <CALayer: 0x5c82e80>>
)

(gdb) po [[self tableView] indexPathsForVisibleRows]
<__NSArrayM 0x70c95a0>(
<NSIndexPath 0x5c555e0> 2 indexes [0, 0],
<NSIndexPath 0x5c78690> 2 indexes [0, 1],
<NSIndexPath 0x5c7b910> 2 indexes [0, 2],
<NSIndexPath 0x5c7ea60> 2 indexes [0, 3],
<NSIndexPath 0x5c69c90> 2 indexes [0, 4]
)

(gdb) po indexPath
<NSIndexPath 0x5c555e0> 2 indexes [0, 0]
(gdb) p (int)[cell retainCount]
$3 = 2
gdb) po cell
<HaveNeedTableViewCell: 0x5c76720; baseClass = UITableViewCell; frame = (0 0; 280 44); autoresize = W; layer = <CALayer: 0x5c73740>>
(gdb) p (int)[cell isSelected]
$4 = 96954113
(gdb)

Any thoughts? Right now, I'm just going to turn off the selection blink animation, but it's frustrating me.

Your help is appreciated!

Ron C

 

[PhoneyDeveloper]

cell.isSelected must return a BOOL, which you can't print with %@. Try %d.