/** Popover item subclass */

@implementation NXWindowListPopoverItem

-(void)commonInit{
    NSTouchBar* touchBar = [NXWindowListTouchBar new];
    self.popoverTouchBar = touchBar;
    self.pressAndHoldTouchBar = touchBar;
    self.customizationLabel = nil;
    self.collapsedRepresentationImage = [[NSBundle bundleForClass:self.class] imageForResource:@"NXWindowListIcon"];
}

-(instancetype)initWithCoder:(NSCoder *)coder{
    self = [super initWithCoder:coder];
    [self commonInit];
    return self;
}
-(instancetype)initWithIdentifier:(NSTouchBarItemIdentifier)identifier{
    self = [super initWithIdentifier:identifier];
    [self commonInit];
    return self;
}
......
@end



/** subtouchbar subclass */

@implementation NXWindowListTouchBar{ ... }
-(void)commonInit{
    self.delegate = self;
    scrubberIdentifier = @"NXTouchBarWindowListTouchBarScrubberItem";
    subTouchBarIdentifier = @"NXTouchBarWindowListTouchBar";
    self.customizationIdentifier = subTouchBarIdentifier;
    self.defaultItemIdentifiers = @[scrubberIdentifier];
    self.customizationAllowedItemIdentifiers = @[scrubberIdentifier];
}


-(instancetype)initWithCoder:(NSCoder *)coder{
    self = [super initWithCoder:coder];
    [self commonInit];
    return self;
}
-(instancetype)init{
    self = [super init];
    [self commonInit];
    return self;
}
...
@end