Developing Apps With WatchKit

Adam ShawKabuki Vision

A Whirlwind Tour

@KabukiVision

Dressed NoteMaster Journaling

WatchKit• SDK for building apps for Apple Watch

• Similar, but different from iOS app development

• Very limited

• Can’t build true “native” apps

• Need

• Xcode (Mac)

• Apple Watch

• iPhone

WatchKit ExtensionsWatchKit app is an extension to an iPhone app.

“Starting later next year, developers will be able to create fully native apps for Apple Watch.”

— Apple, Nov 2014

WatchKit Extensions

• WatchKit App

• Glance (optional)

• Notification (optional)

Architecture

WatchKit AppStoryboard

Resources

WatchKit ExtensionCode!

Resources

iPhone AppCode

Resources

WatchKitWatchKit

Architecture

WatchKit ExtensionCode Resources

WatchKit

iPhone AppCode Resources

Shared Data

Limited Communication

Architecture

• WatchKit app distributed as part of iOS app

• WatchKit code in “WatchKit extension”

• None of your code runs on the watch!

• All of your WatchKit extension code runs on iPhone (in separate background process from main app)

Things you CANNOT do

Hardware sensors (heart rate, step counter, accelerometer, etc)

Things you CANNOT do

Wireless Communications

Things you CANNOT do

Core Animation

CAN animate as sequence of images (like an animated GIF)

Things you CANNOT do

Multi-touch gestures Swiping, dragging, etc.

Things you CANNOT do

Direct access to speaker or microphone

What CAN you do?• Basically:

• Put stuff on the screen

• Respond to simple button taps

• Use iPhone features (GPS, networking, etc.)

• Change stuff on the screen

UI created using storyboards in Xcode’s Interface Builder

User InterfaceStoryboards

User InterfaceInterface Elements

• Text labels, buttons, images

• Switches, sliders, separators, maps

• “Text” input (via voice)

• Groups

• Tables

• Everything must be defined in the storyboard

• No dynamic creation of interface elements in code (mostly)

• Most attributes (color, image, text, etc) can be controlled in code

• “Hidden” attribute can be used to effectively add/remove elements from the interface

• Table “rows” are the only elements that can be dynamically added/removed in code

User InterfaceInterface Elements

• All layout defined in storyboards

• No auto layout, no explicit positioning

• Relative positioning - interface objects laid out vertically or horizontally

• Content expands downward, allowing vertical scrolling

• Two different watch sizes

User InterfaceInterface Layout

User InterfaceInterface Navigation

Hierarchical Page-based Modal

Can’t mix and match hierarchical and page-based (at the same level)

User InterfaceImages

WatchKit AppInstalled Images

WatchKit Extension

Code!Cached Images

Sharing DataWatchKit extension & iOS app

WatchKit ExtensionSandbox

iPhone App

Shared Data

Sandbox

App Group XYZ

App Group XYZ

CommunicationWatchKit extension & iOS app

WatchKit ExtensionSandbox

iPhone AppSandbox

openParentApplication:reply

application:handleWatchKitExtensionRequest:reply:

CommunicationWatchKit extension & iOS app

WatchKit ExtensionSandbox

iPhone AppSandbox

Darwin Notifications (MMWormhole)

Networking

WatchKit ExtensionSandbox

iPhone AppSandbox

openParentApplication:reply

application:handleWatchKitExtensionRequest:reply:

???

Shared Data

Gotchas

• Unpredictable and merciless lifecycle

• WatchKit extension can and will be killed at any time without warning

• User puts down wrist

• Screen timeout

Gotchas• UI Performance

• Communication speed and latency between iPhone and Apple Watch

• Dynamically generated images sent over to watch from iPhone

• Watch not fast at loading images, period

• Reacting to button taps are a two-way trip

Gotchas

• Permissions (contacts, images, location etc.)

• Only main iOS app can trigger these

THANKS!

Adam ShawKabuki Vision

@KabukiVision

Dressed NoteMaster Journaling