Mac Forum / Programming / Mac Programming / February 2008

OK I subclassed NSLevelIndicatorCell to VALevelIndicatorcell taking a
cue from a similar issue with NSTextFieldCell as follows:

#import <Cocoa/Cocoa.h>
@interface VALevelIndicatorCell : NSLevelIndicatorCell
{
@private
  BOOL _vAlign;
}
- (BOOL)isVerticallyAligned;
- (void)setVerticalAlignment:(BOOL)value;
@end

#import "VALevelIndicatorCell.h"
@implementation VALevelIndicatorCell
- (id) init
{
  if (self = [super init])
  {
    _vAlign = TRUE;
  }
  return self;
}

- (void)drawWithFrame:(NSRect)frame inView:(NSView *)controlView
{
  if (_vAlign)
  {
    int i = (frame.size.height - [self cellSize].height)/2;
    frame.origin.y += i;
    frame.size.height -= i;
  }
  [super drawWithFrame:frame inView:controlView];
}

- (BOOL) isVerticallyAligned
{
  return _vAlign;
}

- (void) setVerticalAlignment:(BOOL)value
{
  _vAlign = value;
}
@end

which visually appears centered but the cell doesn't respond to user
actions (i.e., acts like it's disabled). I had set the cell's class to
my class in IB, and primed the column's cell in my table view like this

- (void)awakeFromNib
{
  // Vertically align our start column control
  NSTableColumn * column = [tableView tableColumnWithIdentifier:@"1"];
  VALevelIndicatorCell * cell = [column dataCell];
  [cell setVerticalAlignment:YES];
}

So while I visually got the results I was seeking, the column's cell
isn't responsive; what'd I miss?

Ok, let's try again, using

  http://www.mikeash.com/?page=pyblog/custom-nscells-done-right.html

as a guide and the fix suggested for nested cells, I came up with this
sub-class of a level indicator:

  #import <Cocoa/Cocoa.h>
  @interface VALevelIndicatorCell : NSLevelIndicatorCell {} @end
  @implementation VALevelIndicatorCell

  + (Class)cellClass
  {
    return [VALevelIndicatorCell class];
  }

  - (void)drawWithFrame:(NSRect)frame inView:(NSView *)controlView
  {
    int i = (frame.size.height - [self cellSize].height)/2;
    frame.origin.y += i;
    frame.size.height -= i;

    [super drawWithFrame:frame inView:controlView];
  }
  @end

While I find my draw method does get called, and the cell does get drawn
centered, no user interaction is possible.

This may or may not be related but I notice that the <go to counterpart>
button for my header goes nowhere, while viewing the .m sources does!

Short or rebuilding the class, is there a way to mend a counterpart's
linkage (header or source)?