touchBar(_ touchBar: NSTouchBar, makeItemForIdentifier identifier: NSTouchBarItemIdentifier) -> NSTouchBarItem?

ViewController.swift

// ViewController.swift

extension ViewController: NSTouchBarDelegate {
    func touchBar(_ touchBar: NSTouchBar, makeItemForIdentifier identifier: NSTouchBarItemIdentifier) -> NSTouchBarItem? {
        switch identifier {
            
        // Increase Item
        case NSTouchBarItemIdentifier.increase:
            let button = NSButton(title: "+", target: self, action: #selector(ViewController.increaseCounter))
            let increaseItem = NSCustomTouchBarItem(identifier: identifier)
            increaseItem.customizationLabel = "Counter +"
            increaseItem.view = button
            return increaseItem
            
        // Decrease Item
        case NSTouchBarItemIdentifier.decrease:
            let button = NSButton(title: "-", target: self, action: #selector(ViewController.decreaseCounter))
            
            let decreaseItem = NSCustomTouchBarItem(identifier: identifier)
            decreaseItem.customizationLabel = "Counter -"
            decreaseItem.view = button
            return decreaseItem
        
        // Counter Label
        case NSTouchBarItemIdentifier.counter:
            let label = NSTextField(string: "0")
            label.textColor = NSColor.green
            label.alignment = .center
            label.bind("stringValue", to: self, withKeyPath: #keyPath(currentCounter), options: nil)
            
            let counter = NSCustomTouchBarItem(identifier: identifier)
            counter.customizationLabel = "Counter"
            counter.view = label
            
            let labelLayout = NSLayoutConstraint.constraints(withVisualFormat: "H:[label(60)]",
                                                             options: [],
                                                             metrics: nil,
                                                             views: ["label": label])
            NSLayoutConstraint.activate(labelLayout)
            
            return counter
        default:
            return nil
        }
    }
}