How apps work
Notifications & SystemUI
The shade, the status bar, and the launcher that is just an app.
4 pages46 min4 interactive6300 words
- 01The evolution of notificationsNotifications went from one ticker line to a structured, permissioned, per-channel surface that the user controls category by category. Each change was about who gets to interrupt whom.intermediate12 mininteractive
- 02The notification pipelinenotify() is asynchronous and crosses Binder twice. Between the call and the pixel there is a service that checks permission, resolves a channel, applies Do Not Disturb and ranking, and hands a parcel to SystemUI.nerd11 mininteractive
- 03SystemUIThe status bar, the shade, quick settings, the lock screen and the navigation bar are all drawn by one privileged app. SystemUI is not part of the framework — it is an APK that holds special powers and can crash without taking the system down.nerd12 mininteractive
- 04The launcherThe home screen is an app with a category filter, not a part of the system. That single fact explains widgets, the recents gesture, why you can replace it, and why a launcher crash does not break the phone.intermediate11 mininteractive
Test yourself
Test yourself: Notifications & SystemUI
Why did notification channels change user behaviour more than any earlier feature?