Package limn.scene

Interface Change

All Known Implementing Classes:

Change.State, Change.TextEdit

public sealed interface Change
permits Change.State, Change.TextEdit

What changed on a widget, and what moved it.

Every value but a text edit is interned, so a notification allocates nothing; a text edit allocates one record per edit, and not one per watcher.

This is the payload of the watcher channel (Widget.observeChanges), which hears every change to a widget whatever moved it. The other channel is the handler — the fluent onX slot — which is the application's one response to the user operating the widget, and which runs only for Change.Origin.USER. The whole rule is on Change.Origin.

A change carries no payload beyond the aspect and the origin: it says what changed, and the widget says what it is now. That keeps one type instead of one per widget, keeps every aspect free of boxing, and makes the accessor the single source of truth — at the price of one obligation, which is that no widget announces a state aspect that no public accessor answers.

See Also:

• ChangeObserver

Nested Class Summary

Nested Classes

Modifier and Type	Interface	Description
static enum	Change.Aspect	What about the widget changed.
static enum	Change.Origin	What moved the change, and the whole of this record's rule: The handler runs when, and only when, the user operated this widget.
static final class	Change.State	Every aspect but a text edit; Change.State.aspect() is never Change.Aspect.TEXT.
static final record	Change.TextEdit	A text edit: Change.TextEdit.aspect() is always Change.Aspect.TEXT, so aspect() == TEXT and instanceof Change.TextEdit are the same question in both directions.

Method Summary

Modifier and Type	Method	Description
Change.Aspect	aspect()
static Change.TextEdit	edit(Change.Origin origin, int offset, int removed, int inserted)	A text edit, with the offsets a platform text-changed event wants.
default boolean	fromUser()
static Change	of(Change.Aspect aspect, Change.Origin origin)	The interned value for this pair.
Change.Origin	origin()

Method Details

aspect

Change.Aspect aspect()

Returns:

what about the widget changed

origin

Change.Origin origin()

Returns:

what moved it

fromUser

default boolean fromUser()

Returns:

whether the user operated the widget, which is the only origin a handler runs for

of

static Change of(Change.Aspect aspect,
 Change.Origin origin)

The interned value for this pair. Never allocates.

Parameters:

aspect - what changed; never Change.Aspect.TEXT

origin - what moved it

Returns:

the one instance for the pair

Throws:

IllegalArgumentException - for Change.Aspect.TEXT, which only edit(limn.scene.Change.Origin, int, int, int) can make: TEXT is the one aspect a watcher may narrow on, so it must never arrive as a Change.State and give that watcher a ClassCastException at its own site, with no diagnostic anywhere near the component that announced it

edit

static Change.TextEdit edit(Change.Origin origin,
 int offset,
 int removed,
 int inserted)

A text edit, with the offsets a platform text-changed event wants. Allocates one record per edit, and not one per watcher.

Parameters:

origin - what moved it

offset - where the damaged range begins, in chars

removed - how many chars it replaced

inserted - how many chars it inserted

Returns:

the edit