What events end a running app?

[jtlapp]

Under what circumstances does the device automatically terminate a running app?

Suppose the user wants to be running a particular app most of the time. Will the user have to restart that app after every recharging of the watch? After receiving certain asynchronous notifications? After syncing with the phone?

Context: I'd like to create an app with a watch face. I'm worried that if the app isn't an OS-recognized first-class watch face, there will be occasions where the device exits the app unbeknownst to the user, requiring that the user both recognize this and restart the app. My app needs to be able to asynchronously message to the user all day long, hence the need to also make it a watch face.

[JonFitbit · Accepted solution]

If you create your project as a clock face, it will always be the default application. Users can only have 1 clock face installed at a time.

When a user launches an app, then the clock will be terminated, but it's automatically relaunched when they exit that app.

I don't think there are any other system events which will terminate your clock, except for reboot and the memory pressure event. https://dev.fitbit.com/reference/device-api/system/#interface-memorypressuremonitor-

[jtlapp]

Oh wow. This is a better answer than I was expecting. To clarify, are you saying that I can write a replacement clock face app that will also be able to asynchronously message the user based on conditions of my app's choosing?

I'm asking for clarification, because I imagine that the clock face would have to be able to report phone push notifications too, so the two async notification systems would need to play well together. Also because it's easier for me to imagine that you might restrict a clock face replacement app to be display-only (not receiving user input). Thanks!

[jtlapp]

And can the clock app have multiple screens, including screens not showing the clock? I'm looking to make a full-fledged app that needs to asynchronously message the user throughout the day (unless running a non-clock app), thus requiring the app to also be a clock.

[JonFitbit]

Yes, you can create a clock with messaging. You can use any of the device APIs with clocks or apps.

Clocks do not support buttons, but you can use touch events to navigate to a different screen within a clock.

[jtlapp]

Okay thank you. I guess if I need user input, I'll need to create a clock app and a user input app and have the two communicate via the companion and a web site.

[Sasoj]

The closest I got to was  App Timeout API but it doesn't solve your issue.