NSColorPanel from NSCell

Question

I have a custom NSCell with the following code to display an NSColorPanel when it is clicked:

-(void)setColorFromPanel:(NSColorPanel*)panel{
 NSLog(@"COLOR is HERE!");
 [self setObjectValue:[panel color]];
}

- (NSUInteger)hitTestForEvent:(NSEvent *)event inRect:(NSRect)cellFrame ofView:(NSView *)controlView{
 if(self.isColor){
  if([event type]==NSLeftMouseDown){
   NSColorPanel *panel=[NSColorPanel sharedColorPanel];
   [panel setColor:[self objectValue]];
   [panel setShowsAlpha:YES];
   [panel setAction:@selector(setColorFromPanel:)];
   [panel setTarget:self];
   [panel makeKeyAndOrderFront:nil];
  }
  return NSCellHitContentArea;
 }
    return NSCellHitNone;
}

This code displays a color picker, however, when I click on a color, it crashes. If if remove the [panel setTarget:self] line, then it works fine, albeit with no effect (because I never receive the color value as there is no target).

Here is the stack trace. The error is EXC_BAD_ACCESS.

#0  0x00007fff8667811c in objc_msgSend ()
#1  0x00007fff87081e9a in -[NSApplication sendAction:to:from:] ()
#2  0x00007fff871fa1cd in -[NSColorPanel _forceSendAction:notification:firstResponder:] ()
#3  0x00007fff871fe384 in -[NSColorPanel setColor:] ()
#4  0x00007fff8721d112 in -[NSColorPickerWheel setColor:] ()
#5  0x00007fff8721d5ae in -[NSColorPickerWheel brightnessSlider:] ()
#6  0x00007fff87081e9a in -[NSApplication sendAction:to:from:] ()
#7  0x00007fff87081df9 in -[NSControl sendAction:to:] ()
#8  0x00007fff8710d400 in -[NSCell trackMouse:inRect:ofView:untilMouseUp:] ()
#9  0x00007fff873eaf01 in -[NSSliderCell trackMouse:inRect:ofView:untilMouseUp:] ()
#10 0x00007fff8710c215 in -[NSControl mouseDown:] ()
#11 0x00007fff8702634f in -[NSWindow sendEvent:] ()
#12 0x00007fff86f5ba86 in -[NSApplication sendEvent:] ()
#13 0x00007fff86ef24da in -[NSApplication run] ()
#14 0x00007fff86eeb1a8 in NSApplicationMain ()
#15 0x00000001000029bb in main (argc=1, argv=0x7fff5fbff6a0)

Answer 1

You need to post the relevant part of the crash reports/debugger outputs; otherwise, it's hard to guess exactly what went wrong! We're not psychics, you know. The crash report contains valuable info why it crashed.

That said, there's an open-source color-well cell available here. It's only for GC-enabled app, but should be a good start to build upon, if the license of that code fits your usage. Don't re-invent the wheel.

---

let me add a few words. NSCell in an NSTableView is used as a stamp to draw entries for each row and typically is re-used, and it's not that an NSCell for each row is generated. This doesn't make much sense from the current point of view with abundant memory in a system, but it made sense 15 years ago when NeXTStep was first designed.

Anyway, because of this reason, it's not typically a good idea for a cell to set itself as a target of another object, because that cell tends not to persist. I guess that's what's causing this crash, i.e. NSTableColumn had already released the cell because it finished using that particular cell. It's generally safer to have a controller class as the target of the panel, not the cell itself.