Axis

Small actions. Repeated daily.

Axis is a strength-training app for iPhone and Apple Watch. Build workout routines on your iPhone, run them from your wrist set by set, and see every finished session in your history on the phone. The two apps stay in sync through WatchConnectivity.

Case study: How Axis is designed and built on my portfolio, covering the architecture, code decisions and trade-offs.

Built with SwiftUI, SwiftData, and WatchConnectivity.

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How it works

 iPhone                                         Apple Watch
┌──────────────────────────┐                  ┌──────────────────────────┐
│ Create / edit routines   │ ── templates ──► │ Pick a routine           │
│ (SwiftData)              │  application     │ Track reps & sets        │
│                          │  context         │ Pause / resume timer     │
│ History of completed     │ ◄── workout ──── │ Session complete         │
│ workouts                 │  sendMessage /   │                          │
│                          │  transferUserInfo│                          │
└──────────────────────────┘                  └──────────────────────────┘

1. Plan on iPhone. Create a routine, pick exercises from the built-in library, and set target sets and reps for each one.
2. Train on Apple Watch. Your routines show up on the Watch automatically. Start one, count reps with the + and − buttons, and complete each set. Axis moves to the next exercise on its own.
3. Review on iPhone. When you finish, the Watch sends a summary back to your phone, and the phone saves it to History.

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Features

iPhone

• Routine builder: search a library of 141 exercises and filter it by equipment (barbell, dumbbell, kettlebell, cable, bodyweight, machine)
• Per-exercise targets: set target sets and reps for each exercise, and remove exercises (the order stays in sequence when you do)
• Routine editor: change existing routines; every change syncs to the Watch automatically
• History: a card for each completed workout showing the date, duration, and sets and reps per exercise
• Onboarding: animated launch screen, a greeting, and a one-time guide that also shows whether your Watch is connected

Apple Watch

• Routine picker that lists the routines sent from your iPhone
• Live session: elapsed timer, current exercise, a rep counter with + and − buttons, and set progress ("Set 2 of 4")
• Pause and resume: time spent paused doesn't count toward the workout duration
• Session summary that sends the finished workout back to your iPhone

Time-based theme

Both apps switch between a day theme (7am–7pm) and a night theme automatically. There's no toggle; a timer checks the clock every minute and again whenever the app comes to the foreground.

Accessibility

• VoiceOver-aware onboarding: when VoiceOver is on, the timed transitions wait for you to tap Continue so focus isn't pulled away while it's still reading
• Shared accessibility modifiers in Theme/AccessibilityModifiers.swift

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Architecture

Data model (SwiftData, iPhone)

WorkoutTemplate ──► [TemplateExercise] ──► Exercise          (the plan)
CompletedWorkout ──► [CompletedExercise]                      (what you actually did)

• Exercise: an entry in the exercise library (name, equipment, whether it's custom)
• TemplateExercise: an exercise placed in a routine, with its order and target sets and reps
• WorkoutTemplate: a named routine
• CompletedWorkout / CompletedExercise: a snapshot of a finished session. It's stored separately so editing a routine later never changes past history.

Phone ↔ Watch sync

Only small, lightweight Codable payloads cross the connection. SwiftData models never leave the phone.

Direction	Payload	Transport	Why
iPhone → Watch	[WatchTemplatePayload]	updateApplicationContext	Only the latest set of routines matters, and the Watch gets it the next time it wakes
Watch → iPhone	WatchCompletedWorkoutPayload	sendMessage, falling back to transferUserInfo	Delivered immediately when the phone is reachable; otherwise queued so a finished workout is never lost

On the phone, PhoneConnectivityManager publishes the incoming workout, and RoutinesHome turns it into a CompletedWorkout and saves it.

Watch session logic

WatchWorkoutSession (@Observable) holds all of the in-workout state: rep counting, set completion, moving to the next exercise, the pause and resume clock, and building the payload. The views stay thin, and the logic can be tested without any UI.

Project structure

Axis/                          # iPhone app
├── App/                       # AxisApp, RootView (onboarding flow), AppState
├── Core/
│   ├── Models/                # SwiftData models
│   └── Services/              # PhoneConnectivityManager, Watch payloads
├── Features/
│   ├── Launch/  Onboarding/
│   ├── Routines/              # Home, CreateRoutine, RoutineEditor, exercise library
│   └── History/
└── Theme/                     # Colors, typography, button style, ThemeManager
AxisWatch Watch App/           # watchOS app
├── Services/                  # WatchConnectivityManager, WatchWorkoutSession, theme
└── Views/                     # Greeting, WorkoutSelector, StartedWorkout, WorkoutComplete
AxisTests/                     # iPhone unit tests
AxisWatch Watch AppTests/      # Watch unit tests

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Testing

Both targets use Swift Testing (@Suite / @Test), with about 100 tests in total:

• iPhone (51): converting a Watch payload into a CompletedWorkout, the template and completed-exercise models, EquipmentType, and RoutineEditingLogic (exercise filtering and save validation)
• Watch (51): WatchWorkoutSession from start to finish (rep tracking, completing sets, moving between exercises, the last-exercise check, pausing and resuming, building the payload) and WatchActiveExercise

Run them in Xcode with ⌘U, choosing the iPhone or Watch scheme.

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Getting Started

Requirements

• Xcode 26 or later
• iOS 26.4 or later and watchOS 26.5 or later
• A paired Apple Watch, or a paired iPhone and Apple Watch simulator, to test sync

Run it

git clone https://github.com/arturoa925/Axis.git
cd Axis
open Axis.xcodeproj

1. Set your Team under Signing & Capabilities for the Axis and AxisWatch Watch App targets, and change the bundle IDs (AA.Axis, AA.Axis.watchkitapp) to your own.
2. Run the Axis scheme on an iPhone simulator that has a paired Watch simulator, then run the AxisWatch Watch App scheme on that Watch.
3. Create a routine on the phone. It should appear on the Watch within a few seconds.

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Roadmap

• HealthKit workout sessions on the Watch (heart rate, active calories). CompletedWorkout already has totalCalories and averageHeartRate fields ready for this
• Custom exercises (Exercise.isCustom is already in the model)
• Progress charts in History

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Author

Arturo Ayala: GitHub · LinkedIn