Integrating a Toolbar and Touch Bar into Your App — Apple Sample Code Architecture

Sample CodemacOSReviewed 2026-07-21View on Apple Developer

At a glance

Item	Summary
Purpose	Offer the same font-size and font-style commands through an `NSToolbar` and an `NSTouchBar`.
Architecture	A content view controller owns the text view; one window controller owns command logic and constructs both command surfaces.
Shared state	`currentFontSize` is the binding point between toolbar controls, the touch-bar slider, and text mutations.

Project structure

ToolbarSample/
├── AppDelegate.swift
├── ViewController.swift
├── WindowController.swift
└── WindowController+TouchBar.swift

The touch-bar extension keeps a secondary framework surface separate while reusing the window controller’s formatting commands and state.

Overall architecture

flowchart LR
    AppDelegate --> WindowController
    WindowController --> Toolbar["NSToolbar items"]
    WindowController --> TouchBar["NSTouchBar items"]
    Toolbar --> Commands["font size / style commands"]
    TouchBar --> Commands
    Commands --> TextView["ViewController.NSTextView"]

Reference code

ToolbarSample/WindowController.swift:86 — command logic reaches the single content text view through the window graph.

func contentTextView() -> NSTextView {
    let viewController = self.contentViewController as? ViewController
    return viewController!.textView
}

Ownership and state

classDiagram
    WindowController *-- NSToolbar : outlet and delegate
    WindowController *-- NSTouchBar : creates
    WindowController --> ViewController : content controller
    ViewController *-- NSTextView : outlet
    WindowController *-- Int : currentFontSize
    NSSliderTouchBarItem --> WindowController : value binding

Ownership evidence

ToolbarSample/WindowController.swift:17 — the window controller holds the shared control state and toolbar objects.

class WindowController: NSWindowController, NSToolbarDelegate {
    // ...
}

The storyboard owns initial controller and outlet construction. WindowController is the mutation authority for formatting and control synchronization; ViewController owns the actual text-view outlet and only customizes text-view delegate behavior.

Class and protocol design

Type	Responsibility	Contract
`WindowController`	Command state, text formatting, toolbar factory, printing	`NSToolbarDelegate`
`WindowController` extension	Touch-bar factory and item actions	`NSTouchBarDelegate`
`ViewController`	Hold the editable text view and suppress system text items	`NSTextViewDelegate`
`AppDelegate`	Enable application-wide touch-bar customization UI	`NSApplicationDelegate`

No app-defined protocol is needed because both surfaces call the same concrete command owner through target/action and binding.

Access control

Boundary	Effect and rationale
`private` toolbar identifier extension	Keeps identifier constants file-scoped and prevents unrelated files from depending on them.
`private` touch-bar customization identifier extension	Provides the same namespace boundary for the touch-bar file.
Implicit `internal` controllers and commands	Supports storyboard and cross-file extension access inside the app target only.
`@objc dynamic currentFontSize`	Exposes the property to Cocoa binding/KVO; this is runtime visibility, not `public` API.

The two identifier boundaries are visible at ToolbarSample/WindowController.swift:11 and ToolbarSample/WindowController+TouchBar.swift:10.

Logic ownership and placement

Logic	Owner
Font conversion and selection handling	`WindowController`
Toolbar item factory and allowed/default sets	`WindowController.swift`
Touch-bar item factory	`WindowController+TouchBar.swift`
Text-system touch-bar filtering	`ViewController`
App-wide customization opt-in	`AppDelegate`

Design patterns

Pattern	Evidence	Purpose
Shared command controller	`ToolbarSample/WindowController.swift:94`	One formatting implementation serves two UI surfaces.
Delegate factory	`ToolbarSample/WindowController.swift:281`	Creates toolbar items from identifiers.
Target/action	`ToolbarSample/WindowController+TouchBar.swift:57`	Routes controls to the window command owner.
Cocoa binding	`ToolbarSample/WindowController+TouchBar.swift:83`	Synchronizes the touch-bar slider with shared size state.
Capability extension	`ToolbarSample/WindowController+TouchBar.swift:20`	Isolates touch-bar integration without duplicating the controller.

Naming conventions

Surface-specific code uses a +TouchBar filename while retaining the owning type name.
Commands describe user intent: setTextViewFontSize, setTextViewFont, and changeFontSizeBySlider.
Identifier names mirror controls: fontSize, fontStyle, popover, and popoverSlider.

Architecture takeaways

Route multiple command surfaces through one mutation owner.
Separate framework-specific factories while sharing state and domain commands.
Use file-private identifier namespaces to avoid string scattering.
For a larger app, inject a formatting command object rather than reaching through contentViewController; this sample stays deliberately controller-centric.

Source map

Source	Role
`ToolbarSample/WindowController.swift:17`	Shared command and toolbar owner
`ToolbarSample/WindowController+TouchBar.swift:20`	Touch-bar factory
`ToolbarSample/ViewController.swift:10`	Text-view owner
`ToolbarSample/AppDelegate.swift:14`	Customization opt-in

Official Apple documentation