Trait Widget 

pub trait Widget: Any {
    // Required methods
    fn layout(&mut self, ctx: &mut LayoutCtx<'_>, bc: &BoxConstraints) -> Size;
    fn paint(&mut self, ctx: &mut PaintCtx<'_>, scene: &mut dyn PaintScene);

    // Provided methods
    fn event(
        &mut self,
        _ctx: &mut EventCtx<'_>,
        _event: &InputEvent,
    ) -> EventResult { ... }
    fn semantics(&self, _ctx: &mut SemanticsCtx) { ... }
    fn type_name(&self) -> &'static str { ... }
    fn visit_children(&self, _visitor: &mut dyn FnMut(&ChildPod)) { ... }
}

A retained UI element living in the widget tree.

Widget: Any so the render root can downcast a boxed widget back to the concrete element type its originating view produced (needed during rebuild). Implementing types get [Widget::downcast_mut] for free — no boilerplate method to write.

Required Methods

fn layout(&mut self, ctx: &mut LayoutCtx<'_>, bc: &BoxConstraints) -> Size

Choose a size within bc and return it. The chosen size must satisfy bc (callers may additionally clamp via BoxConstraints::constrain).

fn paint(&mut self, ctx: &mut PaintCtx<'_>, scene: &mut dyn PaintScene)

Emit draw commands for this widget into scene.

Paint may advance a widget’s own animation state (e.g. a scroll fling integrated from a monotonic clock) as a v1 seam. A widget that does so must call PaintCtx::request_frame while the animation is still running so the shell re-invokes paint absent any external event — otherwise the desktop ControlFlow::Wait loop idles and the animation stalls. It must stop signalling once the animation reaches rest.

Provided Methods

fn event(&mut self, _ctx: &mut EventCtx<'_>, _event: &InputEvent) -> EventResult

Handle an input event, optionally mutating application state through ctx and reporting whether it was consumed.

Defaulted to EventResult::Ignored so non-interactive widgets are unaffected. Interactive widgets (Button/Checkbox/Slider) override this; containers forward to their ChildPod children via ChildPod::event_child.

fn semantics(&self, _ctx: &mut SemanticsCtx)

Contribute this widget’s accessibility node(s) into ctx.

Defaulted to a no-op so non-semantic widgets (and every widget written before this seam) are unaffected — exactly like Widget::event. A leaf widget overrides it to call SemanticsCtx::push_node with its role and state; a container overrides it to forward to each child via ChildPod::semantics_child (a transparent container contributes no node of its own, only recursion). The pass runs after layout, so SemanticsCtx::origin/SemanticsCtx::size carry valid absolute geometry.

fn type_name(&self) -> &'static str

This widget’s concrete type name, for read-only tooling.

Defaulted to core::any::type_name of the implementing type, so every widget reports its own name through the vtable — including one reached as a dyn Widget, where the concrete type is otherwise unrecoverable. Asking the live widget beats recording a name when it was built: a rebuild that swaps a child’s concrete type cannot leave a stale name behind, not even through the doubly-erased pods no reconciler can observe (docs/LIMITATIONS.md’s focus-double-erasure-swap-blind).

Diagnostic only: type_name’s output is not a stable contract across compiler versions, so never parse or match on it. Overriding it is sanctioned only for a transparent wrapper reporting what it wraps (the Box<dyn Widget> blanket impl is the one in-crate case).

fn visit_children(&self, _visitor: &mut dyn FnMut(&ChildPod))

Visit this widget’s owned ChildPods, in declaration (paint) order — the read-only seam that makes the retained hierarchy enumerable.

Containers own their children as ChildPod fields rather than as arena nodes (see ChildPod), so nothing outside a container could walk into its subtree; this is that walk, and WidgetTree::inspect is its one in-crate consumer.

Defaulted to visiting nothing, exactly like Widget::event and Widget::semantics: a leaf widget needs no impl and pays nothing, and a container that never overrides it simply reads as a leaf to tooling. It runs behind &self and must not mutate anything a pass depends on — no build/layout/paint/event behavior may be routed through it.

No cycles by construction. A ChildPod owns its widget (Box<dyn Widget>); ownership is a tree, so a descent through visit_children terminates without any runtime cycle check. A widget that handed the visitor a pod it does not own would break that, which is why the visitor takes &ChildPod — there is no way to publish a shared one.

Implementations

impl dyn Widget

pub fn downcast_mut<W>(&mut self) -> Option<&mut W>

where W: Widget,

Attempt to downcast this trait object to a concrete widget type.

Uses trait upcasting (Widget: Any, stable since Rust 1.86; the workspace MSRV is 1.88) — no unsafe.

Trait Implementations

impl Widget for Box<dyn Widget>

A boxed widget is itself a Widget, delegating every pass to its contents.

This blanket impl is what makes type-erased children work: a crate::view::AnyView’s element is a Box<dyn Widget>, and View::Element must implement Widget — so the box has to be a widget too. It also lets a Box<dyn Widget> be stored inside a ChildPod like any concrete widget. Box<dyn Widget> is 'static (hence Any), so it satisfies the Widget: Any bound and can be recovered by [downcast_mut](dyn Widget::downcast_mut) during rebuild.

fn type_name(&self) -> &'static str

Report the boxed widget’s name, not Box<dyn Widget> — the box is a storage detail of type erasure, never a tree element in its own right, and it nests (a doubly-boxed pod resolves through both layers).

fn layout(&mut self, ctx: &mut LayoutCtx<'_>, bc: &BoxConstraints) -> Size

Choose a size within bc and return it. The chosen size must satisfy bc (callers may additionally clamp via BoxConstraints::constrain).

fn paint(&mut self, ctx: &mut PaintCtx<'_>, scene: &mut dyn PaintScene)

Emit draw commands for this widget into scene.

fn event(&mut self, ctx: &mut EventCtx<'_>, event: &InputEvent) -> EventResult

Handle an input event, optionally mutating application state through ctx and reporting whether it was consumed.

fn semantics(&self, ctx: &mut SemanticsCtx)

Contribute this widget’s accessibility node(s) into ctx.

fn visit_children(&self, visitor: &mut dyn FnMut(&ChildPod))

Visit this widget’s owned ChildPods, in declaration (paint) order — the read-only seam that makes the retained hierarchy enumerable.

Dyn Compatibility

This trait is dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety".

Implementations on Foreign Types

impl Widget for AlignWidget

fn layout(&mut self, ctx: &mut LayoutCtx<'_>, bc: &BoxConstraints) -> Size

fn paint(&mut self, ctx: &mut PaintCtx<'_>, scene: &mut dyn PaintScene)

fn event(&mut self, ctx: &mut EventCtx<'_>, event: &InputEvent) -> EventResult

fn semantics(&self, ctx: &mut SemanticsCtx)

fn visit_children(&self, visitor: &mut dyn FnMut(&ChildPod))

impl Widget for Box<dyn Widget>

A boxed widget is itself a Widget, delegating every pass to its contents.

This blanket impl is what makes type-erased children work: a crate::view::AnyView’s element is a Box<dyn Widget>, and View::Element must implement Widget — so the box has to be a widget too. It also lets a Box<dyn Widget> be stored inside a ChildPod like any concrete widget. Box<dyn Widget> is 'static (hence Any), so it satisfies the Widget: Any bound and can be recovered by [downcast_mut](dyn Widget::downcast_mut) during rebuild.

fn type_name(&self) -> &'static str

Report the boxed widget’s name, not Box<dyn Widget> — the box is a storage detail of type erasure, never a tree element in its own right, and it nests (a doubly-boxed pod resolves through both layers).

fn layout(&mut self, ctx: &mut LayoutCtx<'_>, bc: &BoxConstraints) -> Size

fn paint(&mut self, ctx: &mut PaintCtx<'_>, scene: &mut dyn PaintScene)

fn event(&mut self, ctx: &mut EventCtx<'_>, event: &InputEvent) -> EventResult

fn semantics(&self, ctx: &mut SemanticsCtx)

fn visit_children(&self, visitor: &mut dyn FnMut(&ChildPod))

impl Widget for ButtonWidget

fn layout(&mut self, ctx: &mut LayoutCtx<'_>, bc: &BoxConstraints) -> Size

fn paint(&mut self, ctx: &mut PaintCtx<'_>, scene: &mut dyn PaintScene)

fn event(&mut self, ctx: &mut EventCtx<'_>, event: &InputEvent) -> EventResult

fn semantics(&self, ctx: &mut SemanticsCtx)

fn visit_children(&self, visitor: &mut dyn FnMut(&ChildPod))

impl Widget for CheckboxWidget

fn layout(&mut self, ctx: &mut LayoutCtx<'_>, bc: &BoxConstraints) -> Size

fn paint(&mut self, ctx: &mut PaintCtx<'_>, scene: &mut dyn PaintScene)

fn event(&mut self, ctx: &mut EventCtx<'_>, event: &InputEvent) -> EventResult

fn semantics(&self, ctx: &mut SemanticsCtx)

fn visit_children(&self, visitor: &mut dyn FnMut(&ChildPod))

impl Widget for FlexWidget

fn layout(&mut self, ctx: &mut LayoutCtx<'_>, bc: &BoxConstraints) -> Size

fn paint(&mut self, ctx: &mut PaintCtx<'_>, scene: &mut dyn PaintScene)

fn event(&mut self, ctx: &mut EventCtx<'_>, event: &InputEvent) -> EventResult

fn semantics(&self, ctx: &mut SemanticsCtx)

fn visit_children(&self, visitor: &mut dyn FnMut(&ChildPod))

impl Widget for GestureDetectorWidget

fn layout(&mut self, ctx: &mut LayoutCtx<'_>, bc: &BoxConstraints) -> Size

fn paint(&mut self, ctx: &mut PaintCtx<'_>, scene: &mut dyn PaintScene)

fn event(&mut self, ctx: &mut EventCtx<'_>, event: &InputEvent) -> EventResult

fn semantics(&self, ctx: &mut SemanticsCtx)

fn visit_children(&self, visitor: &mut dyn FnMut(&ChildPod))

impl Widget for HeroWidget

fn layout(&mut self, ctx: &mut LayoutCtx<'_>, bc: &BoxConstraints) -> Size

fn paint(&mut self, ctx: &mut PaintCtx<'_>, scene: &mut dyn PaintScene)

fn event(&mut self, ctx: &mut EventCtx<'_>, event: &InputEvent) -> EventResult

fn semantics(&self, ctx: &mut SemanticsCtx)

fn visit_children(&self, visitor: &mut dyn FnMut(&ChildPod))

impl Widget for IconButtonWidget

fn layout(&mut self, ctx: &mut LayoutCtx<'_>, bc: &BoxConstraints) -> Size

fn paint(&mut self, ctx: &mut PaintCtx<'_>, scene: &mut dyn PaintScene)

fn event(&mut self, ctx: &mut EventCtx<'_>, event: &InputEvent) -> EventResult

fn semantics(&self, ctx: &mut SemanticsCtx)

fn visit_children(&self, visitor: &mut dyn FnMut(&ChildPod))

impl Widget for ImageWidget

fn layout(&mut self, _ctx: &mut LayoutCtx<'_>, bc: &BoxConstraints) -> Size

fn paint(&mut self, ctx: &mut PaintCtx<'_>, scene: &mut dyn PaintScene)

impl Widget for PaddingWidget

fn layout(&mut self, ctx: &mut LayoutCtx<'_>, bc: &BoxConstraints) -> Size

fn paint(&mut self, ctx: &mut PaintCtx<'_>, scene: &mut dyn PaintScene)

fn event(&mut self, ctx: &mut EventCtx<'_>, event: &InputEvent) -> EventResult

fn semantics(&self, ctx: &mut SemanticsCtx)

fn visit_children(&self, visitor: &mut dyn FnMut(&ChildPod))

impl Widget for PinchDetectorWidget

fn layout(&mut self, ctx: &mut LayoutCtx<'_>, bc: &BoxConstraints) -> Size

fn paint(&mut self, ctx: &mut PaintCtx<'_>, scene: &mut dyn PaintScene)

fn event(&mut self, ctx: &mut EventCtx<'_>, event: &InputEvent) -> EventResult

fn semantics(&self, ctx: &mut SemanticsCtx)

fn visit_children(&self, visitor: &mut dyn FnMut(&ChildPod))

impl Widget for PlatformViewWidget

fn layout(&mut self, _ctx: &mut LayoutCtx<'_>, bc: &BoxConstraints) -> Size

fn paint(&mut self, ctx: &mut PaintCtx<'_>, scene: &mut dyn PaintScene)

fn semantics(&self, ctx: &mut SemanticsCtx)

impl Widget for SafeAreaWidget

fn layout(&mut self, ctx: &mut LayoutCtx<'_>, bc: &BoxConstraints) -> Size

fn paint(&mut self, ctx: &mut PaintCtx<'_>, scene: &mut dyn PaintScene)

fn event(&mut self, ctx: &mut EventCtx<'_>, event: &InputEvent) -> EventResult

fn semantics(&self, ctx: &mut SemanticsCtx)

fn visit_children(&self, visitor: &mut dyn FnMut(&ChildPod))

impl Widget for ScaffoldWidget

fn layout(&mut self, ctx: &mut LayoutCtx<'_>, bc: &BoxConstraints) -> Size

fn paint(&mut self, ctx: &mut PaintCtx<'_>, scene: &mut dyn PaintScene)

fn event(&mut self, ctx: &mut EventCtx<'_>, event: &InputEvent) -> EventResult

fn semantics(&self, ctx: &mut SemanticsCtx)

fn visit_children(&self, visitor: &mut dyn FnMut(&ChildPod))

impl Widget for ScrollWidget

fn layout(&mut self, ctx: &mut LayoutCtx<'_>, bc: &BoxConstraints) -> Size

fn paint(&mut self, ctx: &mut PaintCtx<'_>, scene: &mut dyn PaintScene)

fn event(&mut self, ctx: &mut EventCtx<'_>, event: &InputEvent) -> EventResult

fn semantics(&self, ctx: &mut SemanticsCtx)

fn visit_children(&self, visitor: &mut dyn FnMut(&ChildPod))

impl Widget for ShieldWidget

fn layout(&mut self, ctx: &mut LayoutCtx<'_>, bc: &BoxConstraints) -> Size

fn paint(&mut self, ctx: &mut PaintCtx<'_>, scene: &mut dyn PaintScene)

fn event(&mut self, ctx: &mut EventCtx<'_>, event: &InputEvent) -> EventResult

fn semantics(&self, ctx: &mut SemanticsCtx)

fn visit_children(&self, visitor: &mut dyn FnMut(&ChildPod))

impl Widget for SizedBoxWidget

fn layout(&mut self, ctx: &mut LayoutCtx<'_>, bc: &BoxConstraints) -> Size

fn paint(&mut self, ctx: &mut PaintCtx<'_>, scene: &mut dyn PaintScene)

fn event(&mut self, ctx: &mut EventCtx<'_>, event: &InputEvent) -> EventResult

fn semantics(&self, ctx: &mut SemanticsCtx)

fn visit_children(&self, visitor: &mut dyn FnMut(&ChildPod))

impl Widget for SliderWidget

fn layout(&mut self, _ctx: &mut LayoutCtx<'_>, bc: &BoxConstraints) -> Size

fn paint(&mut self, ctx: &mut PaintCtx<'_>, scene: &mut dyn PaintScene)

fn event(&mut self, ctx: &mut EventCtx<'_>, event: &InputEvent) -> EventResult

fn semantics(&self, ctx: &mut SemanticsCtx)

impl Widget for StackWidget

fn layout(&mut self, ctx: &mut LayoutCtx<'_>, bc: &BoxConstraints) -> Size

fn paint(&mut self, ctx: &mut PaintCtx<'_>, scene: &mut dyn PaintScene)

fn event(&mut self, ctx: &mut EventCtx<'_>, event: &InputEvent) -> EventResult

fn semantics(&self, ctx: &mut SemanticsCtx)

fn visit_children(&self, visitor: &mut dyn FnMut(&ChildPod))

impl Widget for TextInputWidget

fn layout(&mut self, ctx: &mut LayoutCtx<'_>, bc: &BoxConstraints) -> Size

fn paint(&mut self, ctx: &mut PaintCtx<'_>, scene: &mut dyn PaintScene)

fn event(&mut self, ctx: &mut EventCtx<'_>, event: &InputEvent) -> EventResult

fn semantics(&self, ctx: &mut SemanticsCtx)

impl Widget for TextWidget

fn layout(&mut self, ctx: &mut LayoutCtx<'_>, bc: &BoxConstraints) -> Size

fn paint(&mut self, ctx: &mut PaintCtx<'_>, scene: &mut dyn PaintScene)

fn semantics(&self, ctx: &mut SemanticsCtx)

impl<State> Widget for NavigatorWidget<State>

where State: 'static,

fn semantics(&self, ctx: &mut SemanticsCtx)

R23 — semantics forwarding follows input routing, exactly.

A transparent container (like Stack): the navigator contributes no node of its own and forwards ChildPod::semantics_child for exactly the pages input_routed_pages says an input event could reach — today { pages.last() }. Every other page is omitted: no node, no recursion. Offering a screen-reader user a control they physically cannot activate is worse than not offering it, so the two reaches are derived from one function rather than kept in sync by hand.

This omits more than paint culling does

A page under a transparent overlay is PageVisibility::Visible — still painted — yet it is omitted here, because R23 tracks input routing, not painting, and route_top routes only to the top page. The divergence is deliberate: it is what makes a modal modal to assistive technology for free (the page beneath a dialog is already inert to a finger). The topmost transparent page — the dialog itself — is forwarded, since it is pages.last().

Why omission and not an accesskit flag

Not hidden: it would need a synthesized per-page wrapper node to carry the flag (churning node ids on every navigation for nodes that exist only to say “ignore me”), it would publish the stale bounds of a covered page that layout skipped, and whether every platform adapter honours the flag is unverified — omission needs no such trust. Not clips_children, which asserts overflow: hidden and would be simply false here. Not modal, which is the right flag but belongs on the dialog widget: the navigator does not know a page is a dialog and cannot infer it from BackPolicy (most shipped modals push through push_transparent_for_result and so take the default BackPolicy::Pop).

During a transition

No special case: pages.last() is the destination page for a push, pop and replace alike, and its mid-flight bounds are the animated pod origins paint is using — consistent with the screen and self-correcting within one transition. Input is fully suppressed mid-transition (event_at), so a screen reader activating a node during those ≤340ms hits exactly the same suppression a finger would.

fn layout(&mut self, ctx: &mut LayoutCtx<'_>, bc: &BoxConstraints) -> Size

fn paint(&mut self, ctx: &mut PaintCtx<'_>, scene: &mut dyn PaintScene)

fn event(&mut self, ctx: &mut EventCtx<'_>, event: &InputEvent) -> EventResult

fn visit_children(&self, visitor: &mut dyn FnMut(&ChildPod))

impl<State> Widget for OverlayPortalWidget<State>

where State: 'static,

fn layout(&mut self, ctx: &mut LayoutCtx<'_>, bc: &BoxConstraints) -> Size

fn paint(&mut self, ctx: &mut PaintCtx<'_>, scene: &mut dyn PaintScene)

fn event(&mut self, ctx: &mut EventCtx<'_>, event: &InputEvent) -> EventResult

fn semantics(&self, ctx: &mut SemanticsCtx)

fn visit_children(&self, visitor: &mut dyn FnMut(&ChildPod))

Implementors

impl Widget for AnimatedOpacityWidget

impl Widget for AnimatedScaleWidget

impl Widget for CanvasWidget

impl Widget for ContainerWidget

impl Widget for DividerWidget

impl Widget for IconWidget

impl Widget for ListViewWidget

impl Widget for PanZoomWidget

impl Widget for RadioWidget

impl<C> Widget for ComponentWidget<C>

where C: Component,

impl<P> Widget for PatternSwitcherWidget<P>

where P: TransitionPattern + Clone + 'static,