Enum Lifecycle 

pub enum Lifecycle {
    WillLaunch,
    DidLaunch,
    DidBecomeActive,
    WillResignActive,
    WillEnterForeground,
    DidEnterBackground,
    DidReceiveMemoryWarning,
    WillTerminate,
    DidExit,
}

An app-lifecycle phase (docs/lifecycle.md). Each backend maps these onto its OS’s native app / activity delegate. Some phases only exist on some platforms (a mobile app enters the background and can be low on memory, a desktop app cannot), so Lifecycle::is_universal marks the ones every backend delivers, and Toolkit::supports_lifecycle reports per-backend truth.

Rough native mapping:

phase	AppKit	UIKit	GTK	Qt	Android	XAML
WillLaunch / DidLaunch	applicationWill/DidFinishLaunching	same	startup/mount	mount	onCreate	window create
DidBecomeActive	didBecomeActive	didBecomeActive	notify::is-active	ApplicationActive	onResume	Activated
WillResignActive	willResignActive	willResignActive	notify::is-active	ApplicationInactive	onPause	Deactivated
WillEnterForeground	—	willEnterForeground	—	—	onStart	—
DidEnterBackground	—	didEnterBackground	—	—	onStop	—
DidReceiveMemoryWarning	—	didReceiveMemoryWarning	—	—	onTrimMemory	—
WillTerminate	willTerminate	willTerminate	shutdown	aboutToQuit	onDestroy	window close
DidExit	after willTerminate	after willTerminate	run returned	exec returned	after onDestroy	loop returned

Variants

WillLaunch

Before the window and UI are built: the first thing to run. Set up global state here.

DidLaunch

The UI is mounted and the app is about to start running. Kick off startup work here.

DidBecomeActive

The app came to the foreground and is the active, focused app receiving input.

WillResignActive

The app is about to stop being active (an interruption, app switch, or losing focus).

WillEnterForeground

The app is about to return to the foreground (mobile). Refresh what background invalidated.

DidEnterBackground

The app left the foreground and is no longer visible (mobile). Persist state, release UI work.

DidReceiveMemoryWarning

The system is low on memory (mobile). Drop caches and non-essential memory now.

WillTerminate

The app is about to terminate: the last chance to save. Triggered by the Quit command, the platform’s quit shortcut, or the OS reclaiming the app.

DidExit

The run loop is over and nothing of the app will run after this: the last phase, after every WillTerminate handler. Day logs its exit line (“Clean exit for …”) once the handlers have run, so a handler here is the app’s last word before it.

Implementations

impl Lifecycle

pub const ALL: [Lifecycle; 9]

Every phase, in delivery order (launch → run → quit). Handy for logging/registration sweeps.

pub const fn is_universal(self) -> bool

True for phases every backend delivers (launch, activation, termination). The remaining phases (WillEnterForeground, DidEnterBackground, DidReceiveMemoryWarning) are mobile concepts and are only delivered by the mobile backends. const so it composes into a backend’s const fn lifecycle_supported and thus into compile-time guards.

pub const fn name(self) -> &'static str

A stable, human-readable name (for logs/warnings).

Trait Implementations

impl Clone for Lifecycle

fn clone(&self) -> Lifecycle

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for Lifecycle

impl Debug for Lifecycle

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Eq for Lifecycle

impl Hash for Lifecycle

fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl PartialEq for Lifecycle

fn eq(&self, other: &Lifecycle) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl StructuralPartialEq for Lifecycle