lifecycle

Documentation

Overview

Package lifecycle defines an event for an app's lifecycle.

The app lifecycle consists of moving back and forth between an ordered sequence of stages. For example, being at a stage greater than or equal to StageVisible means that the app is visible on the screen.

A lifecycle event is a change from one stage to another, which crosses every intermediate stage. For example, changing from StageAlive to StageFocused implicitly crosses StageVisible.

Crosses can be in a positive or negative direction. A positive crossing of StageFocused means that the app has gained the focus. A negative crossing means it has lost the focus.

See the golang.org/x/mobile/app package for details on the event model.

Index

• type Cross
  • func (c Cross) String() string
• type Event
  • func (e Event) Crosses(s Stage) Cross
  • func (e Event) String() string
• type Stage
  • func (s Stage) String() string

Types

type Cross

type Cross uint32

Cross is whether a lifecycle stage was crossed.

const (
	CrossNone Cross = 0
	CrossOn   Cross = 1
	CrossOff  Cross = 2
)

func (Cross) String

func (c Cross) String() string

type Event

type Event struct {
	From, To Stage

	// DrawContext is the state used for painting, if any is valid.
	//
	// For OpenGL apps, a non-nil DrawContext is a gl.Context.
	//
	// TODO: make this an App method if we move away from an event channel?
	DrawContext interface{}
}

Event is a lifecycle change from an old stage to a new stage.

func (Event) Crosses

func (e Event) Crosses(s Stage) Cross

Crosses reports whether the transition from From to To crosses the stage s:

• It returns CrossOn if it does, and the lifecycle change is positive.
• It returns CrossOff if it does, and the lifecycle change is negative.
• Otherwise, it returns CrossNone.

See the documentation for Stage for more discussion of positive and negative crosses.

func (Event) String

func (e Event) String() string

type Stage

type Stage uint32

Stage is a stage in the app's lifecycle. The values are ordered, so that a lifecycle change from stage From to stage To implicitly crosses every stage in the range (min, max], exclusive on the low end and inclusive on the high end, where min is the minimum of From and To, and max is the maximum.

The documentation for individual stages talk about positive and negative crosses. A positive lifecycle change is one where its From stage is less than its To stage. Similarly, a negative lifecycle change is one where From is greater than To. Thus, a positive lifecycle change crosses every stage in the range (From, To] in increasing order, and a negative lifecycle change crosses every stage in the range (To, From] in decreasing order.

const (
	// StageDead is the zero stage. No lifecycle change crosses this stage,
	// but:
	//	- A positive change from this stage is the very first lifecycle change.
	//	- A negative change to this stage is the very last lifecycle change.
	StageDead Stage = iota

	// StageAlive means that the app is alive.
	//	- A positive cross means that the app has been created.
	//	- A negative cross means that the app is being destroyed.
	// Each cross, either from or to StageDead, will occur only once.
	// On Android, these correspond to onCreate and onDestroy.
	StageAlive

	// StageVisible means that the app window is visible.
	//	- A positive cross means that the app window has become visible.
	//	- A negative cross means that the app window has become invisible.
	// On Android, these correspond to onStart and onStop.
	// On Desktop, an app window can become invisible if e.g. it is minimized,
	// unmapped, or not on a visible workspace.
	StageVisible

	// StageFocused means that the app window has the focus.
	//	- A positive cross means that the app window has gained the focus.
	//	- A negative cross means that the app window has lost the focus.
	// On Android, these correspond to onResume and onFreeze.
	StageFocused
)

func (Stage) String

func (s Stage) String() string