Struct EventCx 

pub struct EventCx<'a> { /* private fields */ }

Read-only context passed to App::on_event / App::on_wheel_event.

Event handlers regularly need post-layout geometry to make a decision — “which room row is under this drop?”, “what size did the lightbox body actually get?” — and the handler’s state owns no node, so it can’t have carried the rect itself. EventCx is the damascene analogue of the DOM’s ambient document: a handle into the retained layout the user is currently looking at, queryable by key (element.getBoundingClientRect() shape). Geometry answers from the last laid-out frame — exactly what’s on screen when the event fires.

Like BuildCx, the struct is opaque so the API stays additive: new accessors don’t break apps that ignore the context.

Implementations

impl<'a> EventCx<'a>

pub fn new() -> Self

Construct an empty context. Headless tests that drive App::on_event directly use this; real hosts chain Self::with_ui_state so geometry queries can answer.

pub fn with_ui_state(self, ui_state: &'a UiState) -> Self

Attach the runtime’s crate::state::UiState so geometry accessors can answer. Hosts call this at every dispatch site; when omitted, the accessors return None.

pub fn rect_of_key(&self, key: &str) -> Option<Rect>

The laid-out rect of the keyed node key, from the layout the user is looking at as this event fires. None when the key is absent from that tree (or no UiState is attached).

This is the first-class shape for “the handler needs to know where a keyed thing landed”: resolving a drop target against row rects on PointerUp, stepping zoom from a body’s fitted size, anchoring app-drawn chrome to a control. The event’s own target rect is already on UiEvent::target; this answers for other keys.

Trait Implementations

impl<'a> Clone for EventCx<'a>

fn clone(&self) -> EventCx<'a>

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl<'a> Copy for EventCx<'a>

impl<'a> Debug for EventCx<'a>

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

Formats the value using the given formatter.

impl<'a> Default for EventCx<'a>

fn default() -> EventCx<'a>

Returns the “default value” for a type.