Live activity

A live activity is a window onto something that is still happening, opened outside the app that owns it. The delivery is four stops away, the match is in the seventieth minute, the flight boards in twenty minutes: all of that changes on its own, and all of it is worth following without unlocking a phone and finding an app. So the system lends the activity a slot, on the lock screen and in a compact form near the top of the display, and the app writes into that slot for as long as the thing is going on. When it ends, the activity ends with it.

The word to keep it apart from is push notification. A notification announces an event: it fires once, says one thing, and from then on it only gets older, so a delivery that has moved twice since is represented by three separate messages nobody wanted. A live activity is a state rather than an event. There is one of it, it is rewritten in place, and its whole value is that the number the reader sees now is the current number. That is also the test for whether something deserves one: if the answer would be the same in an hour, send a notification. And when the activity finishes, it should not leave a live surface sitting there stale; either it retires or it becomes an entry in the notification center like anything else.

Two presentations are usually required and they are not the same design. The compact one gets a handful of characters and one glyph, so it has to carry the single most useful figure and nothing more, which in practice means the time or the count and never the app’s name. The expanded one has room for a title, a progress indicator, and an action or two, and is read deliberately rather than glanced at. Both need to survive the update they exist for: numbers set in tabular figures so the layout does not twitch every time a digit changes, and no reflow when a label goes from “3 stops” to “Arriving”, because a surface that jumps while nobody is touching it reads as broken.

The compact form is often described by the shape of the hardware it sits beside, which is where the confusion with a display cutout comes from. The cutout is the camera housing: a hole in the screen rectangle that a layout has to route around, and it is there whether anything is happening or not. A live activity is content that adopts the space around that hole while there is something to say, and the same activity has to be designed for phones whose housing is a different shape or in a different place. Apple’s Live Activities guidance is blunt about the consequence, which is that an activity has to be legible in every one of its presentations, because the reader does not choose which one they get.