Written by Federico Zanetello

Description: watchOS 8 brings all-new opportunities to keep people up to date on their watch face. With new APIs for the Always-On Retina display and updating complications from Bluetooth devices and background delivery of HealthKit data, it's never been easier to keep your app up to date. Learn about region-based user notifications to leverage location in your app. Explore all the new enhancements to SwiftUI and watchOS that will get you excited to build your next Watch app.

Always-on display dimmed state

• Supported on series 5 and 6
• in watchOS 7, the always-on state showed your app’s UI blurred with the system time overlaid
• when you rebuild your app with the watchOS 8 SDK, your app’s UI will now be shown in a dimmed state instead, and is immediately interactive if someone taps the UI
• You can get notified of of this dimmed state via a new SwiftUI environment property isLuminanceReduced.
• You can respond to this state by highlighting information that’s especially important, and hiding information that should stay private

• In the watch simulator, you click the lock button in the simulator window to simulate a wrist-down event (triggering the dimmed state)

Guidance:

• the transition from active state to the always-on state should feel seamless
• don’t drastically alter the UI or reorganize information
• dim non-essential information and elements, to give more prominence to the piece of information you want to stay highlighted and visible
• if your UI has large elements that are filled with color or imagery, you may want to reduce those elements to be represented with a stroke or dimmed color
• redact or remove sensitive information
• reset animations
• use SwiftUI's TimelineView to tell watchOS 8 that your inactive app needs to update its UI

UI Updates: - Apps with an ongoing, active session (e.g. workout or audio session) can update your UI up to once per second - other apps up to once per minute - assume your app is visible longer than two minutes

HealthKit data

• background delivery of HealthKit data to Watch apps
• new results come up to once per hours
• if you have an active complication, up to four times per hour
• all received results count against background app refresh budget

Update frequency:

• immediate for critical data types (fall events, low blood oxygen saturation, heart rate events)
• hourly or longer for other events

Bluetooth

• from watchOS 4, Bluetooth devices can connect directly to Apple Watch and make use of Core Bluetooth.
• from watchOS 8, Bluetooth devices can connect during background app refresh opportunities that your app’s complications get when they’re on the active watch face
  • this means that your app’s complications can stay up to date with your Bluetooth device and display updated information throughout the day.
  • Background app refresh gives your app’s complications that are on the active watch face up to four opportunities per hour to connect and update.
  • these opportunities will count against your app’s overall background app refresh budget

Guidance: - connect and process your data within a very short period of time - new expiration handler on WKRefreshBackgroundTask, letting you know when you're about to run out of time

Location

• new in watchOS 8, region-based user notifications
  • works similarly to iOS:
    • deliver pre-created local notifications
    • "when in use" location permission required
    • limit the number of regions to only include important POIs near someone or locations they’ve shown explicit intent for

• new Location button, for one-time location authorization without going through authorization prompts each time it’s tapped

• always-on altimeter API, no need location access

More enhancements

• respiratory rate API
• assistive touch
• large accessibility text size
• (Xcode 12.5+) Unit testing and UI testing
• Large titles
• text input improvements:
  • Scribble or Dictation preference is preserved per app
  • quick access to changing between input types while entering text
  • SwiftUI's .searchable API
  • Swipe actions on List
  • Buttons improvements:
  • new roles parameter to let the system know how to present and handle specific button types (e.g. destructive buttons)
  • new controlProminence view modifier, which will give those buttons an additional haptic when tapped.
  • SwiftUI Canvas for rich programmatic drawing