尝试在屏幕关闭时让 Apple Watch 计时器应用程序在后台运行

Question

I am trying to build a timing app for the watch that vibrates every minute just as a way for the user to keep track of time. I have the timer correctly working and vibrating, but once the screen on the watch goes off, it no longer vibrates. Once I wake the screen back up, it goes back to normal.

Right now to send the vibration I am using this:

WKInterfaceDevice.currentDevice().playHaptic(.Stop)

I know this might be some sort of design implementation to save battery life, but obviously the point of my app is to keep the track of time even when the screen is off. Is something like this possible?

Answer 1

To keep a watchOS app running after the screen turns off it is now possible to use the new WKExtendedRuntimeSession commands offered in watchOS 6.

Inside your WatchKit Extension ExtensionDelegate file create an extended runtime session with the following command.

let session = WKExtendedRuntimeSession()

Within this delegate file create an applicationDidBecomeActive() function which watchOS will call when your app becomes active. Inside this function start the ExtendedRuntime Session with the following commands.

session.delegate = self   // self as session handler
session.start()  // start WKExtendedRuntimeSession

An extended runtime session must be started when the app is in the active state.

Note you also need to enable Background Modes within the WatchKit Extension target. Select one of the Session Types that most closely fits the type of app you are creating.

Answer 2

No, it's not currently possible to provide haptic feedback while the screen is off , because your code isn't running when the watch is not awake.

As you imagined, this is due to a battery-saving measure which suspends your watch app when the watch goes to sleep.

For more information, the Apple Developer Forum has a long watchOS 2 thread about NSTimer in background .

For watchOS 2, one solution would be to use a paired app on your phone which handles the background timer and uses local notifications. When the phone is locked, the notification would get sent to your watch. You can also use Watch Connectivity to keep the watch updated with timer details once it is awake.