Struct NavigationRail 

pub struct NavigationRail<Msg = Callback> { /* private fields */ }

A vertical navigation rail (tablet / desktop).

Implementations

impl<Msg: Clone + 'static> NavigationRail<Msg>

pub fn new(selected: usize, on_select: impl Fn(usize) -> Msg + 'static) -> Self

Creates a rail: selected = the active index, on_select(i) on click.

pub fn labels(self, labels: RailLabels) -> Self

When the destinations say what they are. RailLabels::None by default, as the reference’s rail does.

Silent on an extended rail, which labels every destination. The two are different label layouts rather than modes of one another, and the reference forbids the combination outright (navigation_rail.dart:121).

pub fn extended(self, extended: bool) -> Self

The wide form: 256 across instead of 80, with every label beside its glyph instead of under it (navigation_rail.dart:131).

The glyphs keep the 80-pixel column they had, so extending a rail widens it and moves nothing: the destinations stay on the line they were on and the label opens out to the side of them. A rail with room for words is what a desktop window has and a tablet in portrait does not, which is why this is a property and not a size class — the caller knows which it is building.

pub fn group_alignment(self, alignment: f32) -> Self

Where the destinations sit between the rail’s top and bottom: -1.0 against the top (the default), 0.0 centred, 1.0 against the bottom — and every value in between (navigation_rail.dart:205).

Continuous rather than three names, as the reference’s is: a rail whose destinations sit a third of the way down is a thing an application asks for, and a three-valued enum would have to be replaced the first time one did.

It moves the group, which is the destinations plus whichever slot is not pinned. See Self::leading_at_top.

pub fn leading(self, widget: impl Widget<Msg> + 'static) -> Self

The slot above the destinations, where an application puts a floating action button or a menu button (navigation_rail.dart:145).

pub fn leading_boxed(self, widget: Box<dyn Widget<Msg>>) -> Self

Self::leading, for a slot that is already boxed.

pub fn trailing(self, widget: impl Widget<Msg> + 'static) -> Self

The slot below the destinations (navigation_rail.dart:156) — an account switcher, a settings button, the end of the list rather than chrome above it.

pub fn trailing_boxed(self, widget: Box<dyn Widget<Msg>>) -> Self

Self::trailing, for a slot that is already boxed.

pub fn main_axis_alignment(self, alignment: Justify) -> Self

How the destinations are placed along the rail, when there is room to spare (navigation_rail.dart:371).

It is the flexbox question — start, centre, end, or one of the three ways of spreading the spare room between them — asked of the group rather than of the rail around it, so SpaceEvenly puts equal room between every destination and at both ends.

Saying this overrides Self::group_alignment, and not by a rule: the group fills the rail to distribute the room, so there is no room left outside it for an alignment to work in. The reference reaches the same place the same way (navigation_rail.dart:501).

pub fn scrollable(self) -> Self

A rail too short for its destinations scrolls them (navigation_rail.dart:353) rather than running them off the bottom of the screen.

The pinned slots stay put — that is what pinning them is for — and what scrolls is the group: the destinations, plus whichever of Self::leading and Self::trailing was left in it.

Like Self::main_axis_alignment, this leaves Self::group_alignment with nothing to do: a viewport that fills the rail has no spare room to place a group in. A rail scrolls because it has less room than it needs, which is the case where an alignment had no room to work in either.

pub fn use_indicator(self, use_indicator: bool) -> Self

Whether the selected destination gets an indicator behind its glyph (navigation_rail.dart:310). On unless said otherwise, as it is over there.

Turning it off is not just removing a shape. With nothing behind it the glyph stands on the rail’s own surface, so the indicator’s content colour would be a colour for a ground that is not there — the selected destination takes the accent instead, glyph and label both, which is the arrangement the reference keeps for exactly this case (navigation_rail.dart:1221, :1211).

pub fn elevation(self, elevation: f32) -> Self

How far off the page the rail sits (navigation_rail.dart:192). Flat by default, as the reference’s is (:1236).

A raised rail drops its hairline: a shadow and a rule are two ways of saying the same thing, and a widget that draws both says it twice — the lesson Card already carries.

pub fn leading_at_top(self, pinned: bool) -> Self

Whether the leading slot is pinned to the top instead of travelling with the destinations. true by default (navigation_rail.dart:112), which is why Self::group_alignment leaves it where it is.

pub fn trailing_at_bottom(self, pinned: bool) -> Self

Whether the trailing slot is pinned to the bottom. false by default (navigation_rail.dart:113), the other half of the reference’s asymmetry: a leading slot is chrome at the top of the rail, a trailing one is the tail of the list of destinations and moves when the list does.

pub fn item( self, icon: impl Into<DestinationIcon>, label: impl Into<String>, ) -> Self

Adds a destination (glyph + label).

pub fn destinations( self, destinations: impl IntoIterator<Item = NavigationDestination>, ) -> Self

Adds a whole list of destinations declared elsewhere — one navigation, handed to whichever chrome the width called for.

This is the reason NavigationDestination is a value. An application that shows a bar when narrow and a rail when wide used to declare its destinations twice, and the two drifted; now it declares them once.

use frus_widgets::{Icons, NavigationDestination, NavigationRail};

let places = vec![
    NavigationDestination::new(Icons::FAVORITE_BORDER, "Saved")
        .selected_icon(Icons::FAVORITE),
    NavigationDestination::new(Icons::MAIL_OUTLINE, "Inbox").badge(3),
];
let _rail = NavigationRail::new(0, |i| i).destinations(places);

pub fn badge(self, count: u32) -> Self

Adds a notification count to the last destination.

pub fn tooltip(self, message: impl Into<String>) -> Self

What a pointer resting on the last destination is told (navigation_rail.dart:1155).

The case this exists for is a rail: it shows glyphs without labels by default, so the mark is all a destination says about itself, and a mark is not always enough.

pub fn selected_icon(self, icon: impl Into<DestinationIcon>) -> Self

The glyph the last destination shows while it is selected, where that differs from its resting one (navigation_rail.dart:1132).

The reference pairs a stroked icon with its filled version, which is how a selected destination reads as selected without leaning on colour alone.

pub fn disabled(self) -> Self

Marks the last destination inaccessible (navigation_rail.dart:1161): its glyph and its label take the disabled ink, nothing lights under the pointer, it emits no message, and the keyboard steps over it.

pub fn indicator_color(self, color: Color) -> Self

The last destination’s own indicator colour, over the theme’s (navigation_rail.dart:1144) — how one entry marks itself out from the rest.

pub fn indicator_shape(self, shape: ShapeBorder) -> Self

The last destination’s own indicator shape, over the theme’s (navigation_rail.dart:1148).

A pill unless something says otherwise, which is what the reference’s default StadiumBorder is — and what this painted, as a radius worked out from the height, until it could say the word.

pub fn overlay_color(self, overlay: WidgetStateProperty<Color>) -> Self

The last destination’s own highlight, per state (navigation_bar.dart:232): the colour that marks it as focused, hovered or pressed, instead of the framework’s own state layer.

The resolved colour is an overlay as the reference means it: its alpha is how far the ground moves towards it, and its colour is where the ground moves to. A state the property says nothing about falls back to the state layer, so naming one state does not silence the rest.

pub fn label_text_style(self, style: TextStyle) -> Self

The destinations’ labels, over the theme’s and the reference’s.

pub fn badge_text_style(self, style: TextStyle) -> Self

The notification counts, over the theme’s and the reference’s.

pub fn background(self, color: Color) -> Self

The rail’s surface. Unset, the theme’s, then the scheme’s surface — where the reference puts a rail (navigation_rail.dart:1202), a rung below the bottom bar.

Trait Implementations

impl<Msg: Clone + 'static> Widget<Msg> for NavigationRail<Msg>

fn style(&self) -> Style

The rail’s box: its column of destinations, plus the intrusions it was told about.

The rail consumes them; its parent does not (milestone 420). The reference keeps its safe area inside the Material (navigation_rail.dart:553) and takes the leading side, the top and the bottom — never the trailing one, which is where the body is. So the rail’s surface, and the rule down its edge, run the full height of the screen while the destinations stay clear of the notch and the gesture bar.

fn children(&self) -> &[Box<dyn Widget<Msg>>]

The widget’s children (possibly empty).

fn paint(&self, bounds: Rect, status: Status, theme: &Theme, scene: &mut Scene)

Paints the widget’s own decoration, according to its status (hover / focus / cursor / selection) and the current theme.

fn on_click(&self) -> Option<Msg>

Message to emit on click (None = not clickable).

fn opaque(&self) -> bool

Whether a press that lands on this widget and on nothing inside it stops here.

fn key(&self) -> Option<u64>

Stable identity key (independent of the position among siblings). None = positional identity. See crate::Keyed.

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

Short name of the widget — for the inspector and diagnostic dumps. Defaults to the name of the concrete type, without module path or generics (each implementation gets its own monomorphised copy of this default body). Transparent wrappers (Box, crate::Keyed…) delegate to their content.

fn semantics(&self) -> Option<SemanticsProperties>

The widget’s accessibility annotation (role, label, value, state), exposed to assistive technologies through the AccessKit tree. None = no semantics of its own (a layout container — its children, though, may have some). See frus_core::SemanticsProperties.

fn describes(&self) -> Option<Description>

What this widget says about its child’s subtree, when it knows something the child cannot know about itself — the crate::Semantics wrapper, and nothing else so far.

fn on_edit(&self, _edit: &mut Edit, _key: &Key) -> Option<Msg>

Applies a key to the focused widget: mutates the edit state (cursor/selection) and returns a message if the value changes.

fn positional_click( &self, _local_x: f32, _local_y: f32, _width: f32, _height: f32, ) -> Option<Msg>

Positional click: a message emitted according to where the click landed (local coordinates from the widget’s top-left corner, within the width × height box), taking priority over on_click. For clickable sub-regions — e.g. the suffix icon of a crate::TextField (clear / reveal) or a chart point (milestone 221). None (the default) = no sub-region; the shell falls back to on_click.

fn cursor_icon( &self, _local_x: f32, _local_y: f32, _width: f32, _height: f32, ) -> Option<Cursor>

Shape of the system cursor wanted at the local position (local_x, local_y) inside the widget’s width × height box (milestone 205): Some(Cursor::Pointer) over a clickable sub-region (a suffix icon…), None (the default) = no opinion, the shell keeps the default cursor. Does not affect clicking; this is purely the pointer’s appearance on hover.

fn cursor_at( &self, _local_x: f32, _local_y: f32, _width: f32, _scroll_cursor: usize, ) -> Option<usize>

Cursor index matching a local position (px from the widget’s top-left corner) — for placing the caret on click. local_y picks the line in a multi-line field (ignored on a single line).

fn text_metrics( &self, _width: f32, _cursor: usize, ) -> Option<(f32, f32, f32, f32)>

SingleChildScrollView metrics of a multi-line field, for a widget width and a cursor: (content height, visible box height, caret top, caret height), in content space (px). The shell uses them to register the scrollable region and to keep the caret in view. None otherwise.

fn text_viewport(&self, _rect: Rect) -> Option<Rect>

Frame (input box) of a multi-line field within its rect — the area where the text scrolls, below the label. Used to place the scrollbar and the scrollable region exactly on the box. None otherwise.

fn caret_vertical( &self, _width: f32, _cursor: usize, _down: bool, _page: bool, _goal_x: Option<f32>, ) -> Option<(usize, f32)>

Moves the caret vertically in a multi-line field and returns (new index, visual column used).

fn selected_text(&self, _edit: &Edit) -> Option<String>

The currently selected text (for copy/cut).

fn text_value(&self) -> Option<&str>

The field’s whole value, if this widget is a text field — to give the IME its input context (suggestions). None otherwise.

fn replace_value(&self, _value: String) -> Option<Msg>

The message that puts value in this field: the one typing would have produced, for a value the framework restores rather than the user typing it.

fn word_at(&self, _index: usize) -> Option<(usize, usize)>

Range (start, end) of the word around the given index (for double-click).

fn selection_handles( &self, _width: f32, _edit: &Edit, _scroll_y: f32, ) -> Option<[SelectionHandle; 2]>

The two handles of the selection in edit, start then end, for a field width wide whose content is scrolled down by scroll_y — where they are painted, and so where a finger takes them. None when there is no selection, or this is not a text field.

fn shortcut_bindings(&self) -> &[(KeyStroke, Intent)]

Keystrokes this subtree binds to intents — see crate::Shortcuts.

fn shortcut_callbacks(&self) -> &[(KeyStroke, Msg)]

Keystrokes this subtree binds straight to messages — see crate::CallbackShortcuts.

fn action_bindings(&self) -> &[(Intent, Msg)]

Intents this subtree answers — see crate::Actions.

fn action_listeners(&self) -> &[(Intent, Msg)]

Intents this subtree watches without answering — see crate::ActionListener.

fn on_keystroke(&self) -> Option<Rc<dyn Fn(KeyStroke) -> Option<Msg>>>

Every keystroke reaching this subtree, handed to a closure — see crate::KeyboardListener. None (the default) is not a listener.

fn focusable(&self) -> bool

If true, the widget can take keyboard focus (click or Tab).

fn descendants_focusable(&self) -> bool

If false, nothing inside this subtree can take focus — the reference’s ExcludeFocus. A dimmed panel behind a sheet is still drawn and still measured; it simply stops being somewhere Tab can land.

fn focus_skip_traversal(&self) -> bool

If true, this subtree’s focus stops are skipped by Tab while remaining focusable by a click — the reference’s ExcludeFocusTraversal. The two are separate questions: a toolbar button may be reachable with the pointer and still not belong in the keyboard’s order.

fn focus_order(&self) -> Option<f32>

A traversal order for this subtree’s focus stops, smallest first — the reference’s NumericFocusOrder. None leaves them in tree order, which is where everything sits until someone says otherwise.

fn focus_group(&self) -> bool

If true, this subtree is a traversal group: an order set inside it is resolved among its own members and nowhere else, so a reordered dialog does not reshuffle the page behind it.

fn autofill_hints(&self) -> &[AutofillHint]

What this field is for, so the platform can fill it in — see AutofillHint. Empty (the default) is a field that takes no part in autofill at all.

fn autofill_group(&self) -> bool

If true, this subtree’s fields are one form — the reference’s AutofillGroup. A service shown a password with no username beside it has nothing to save the pair under.

fn draws_own_focus(&self) -> bool

If true, the widget draws its focus indicator itself (the driver then does not stroke the generic ring). E.g. TextField.

fn draggable(&self) -> bool

If true, the widget responds to pointer dragging (sliders, handles).

fn on_drag(&self, _fraction: f32) -> Option<Msg>

Message produced while dragging, fraction being the relative horizontal position (0.0..=1.0) within the widget’s bounds.

fn on_drag_start(&self, _fraction: f32) -> Option<Msg>

Message produced when a value drag begins — on the press, before the first on_drag.

fn on_drag_end(&self, _fraction: f32) -> Option<Msg>

Message produced when a value drag ends — on the release, with the fraction the pointer finished on.

fn on_drag_delta(&self, _dx: f32) -> Option<Msg>

Message produced by a horizontal drag expressed as a delta: dx is the movement (logical px) since the last event. For handles that accumulate (column resizing), unlike on_drag (an absolute fraction, e.g. a slider). The shell tries it before on_drag; a widget implements only one of the two.

fn hero_tag(&self) -> Option<u64>

If this widget is a shared element, its tag. Two heroes with the same tag on the two sides of a route transition are one thing in two places. See crate::Hero.

fn drag_payload(&self) -> Option<u64>

If this widget can be picked up and dropped elsewhere, what it carries. See crate::Draggable.

fn drag_needs_long_press(&self) -> bool

Does this item lift on a long press rather than on the first movement? The answer inside a scrollable, where a plain drag belongs to the scroll.

fn drag_ghost_opacity(&self) -> f32

How solid the item left behind looks while a copy of it is being dragged.

fn on_dropped(&self, _accepted: bool) -> Option<Msg>

Message sent when a drag of this item ends, true if a target took it.

fn drop_zone(&self) -> bool

Is this widget a drop target? See crate::DragTarget.

fn accepts_drag(&self, _payload: u64) -> bool

Would this target take payload? Only asked of a drop target.

fn on_drop(&self, _payload: u64) -> Option<Msg>

Message sent when an accepted item is dropped on this target.

fn reorder_index(&self) -> Option<usize>

If this widget is a reorderable header, its column index. The shell uses it to identify the source column (on press) and the target column (under the pointer on release) of a reordering drag.

fn on_reorder(&self, _to: usize) -> Option<Msg>

Message emitted when this header (the source) is dropped on column to. The widget knows its own index and the on_reorder(from, to) callback.

fn reorder_axis(&self) -> ReorderAxis

Movement axis of this reorderable (default ReorderAxis::Horizontal): the shell orients the drag preview (ghost + insertion indicator) accordingly. Kanban cards return ReorderAxis::Vertical.

fn reorder_inserts(&self) -> bool

Is a horizontal reorderable dropped between its neighbours, like a list’s row, rather than into the place of the one under the pointer, like a table’s column? false by default, which is the table.

fn reorder_draggable(&self) -> bool

Can this reorderable be picked up as a drag source? true by default for every reorderable. A target-only slot — the drop zone at the end of a Kanban column — returns false: a card can be dropped there, not lifted from it (otherwise the drag would raise an empty ghost that moves nothing).

fn reorder_droppable(&self) -> bool

Can this reorderable be dropped onto? true by default, and the mirror image of reorder_draggable: a source-only grip — a list row’s drag handle — returns false.

fn reorder_announcement(&self, _to: usize) -> Option<String>

What to say to a screen reader once this reorderable has been moved to to — the spoken counterpart of the ghost, for someone who cannot see it land.

fn announce(&self) -> Option<String>

Text to announce to the screen reader when this widget is activated (mouse click or Enter/Space) — a live region reads it out loud. Describes the effect the activation produced (“Sorted by Name ascending”, “All rows selected”), for the blind user who cannot perceive the visual change. None = nothing to announce (the default).

fn stack(&self) -> bool

If true, the widget is a stack: its children are superimposed layers (the same box), rendered in order (the last one on top).

fn continuous(&self) -> bool

If true, the widget animates continuously (driven by time, not by a target): the framework keeps redrawing. E.g. CircularProgressIndicator.

fn repaint_boundary(&self) -> bool

If true, this widget is a repaint boundary: its subtree is cached (primitives + interaction maps) and reused as is as long as its geometry and the interaction state of its descendants do not change — a widget animating elsewhere no longer forces it to repaint. See crate::Container::repaint_boundary and paintcache.rs.

fn scroll_content(&self) -> Option<&dyn Widget<Msg>>

If the widget is a scrollable container, returns its content.

fn virtual_list(&self, _viewport: Size) -> Option<VirtualList<'_, Msg>>

If the widget is a virtualised list, returns its description (item count, height, factory). Only the visible items are built.

fn page_view(&self) -> Option<PagedView<'_, Msg>>

If the widget is a paged view, returns its description (page count, axis, factory). Like a virtualised list, only the visible pages are built.

fn on_page_changed(&self, _page: usize) -> Option<Msg>

Message sent by a paged view when the page on screen changes.

fn on_scroll(&self, _position: ScrollPosition) -> Option<Msg>

Message sent by a scroll region when its offset changes — the reading half of crate::ScrollPosition.

fn scroll_grain(&self) -> f32

How far this region must move before it says so again, in pixels; 0 — the default — reports every change.

fn intrinsic(&self) -> Option<(IntrinsicAxis, Option<f32>)>

If the widget takes one axis from its content’s preferred size, returns that axis and the step its measurement is rounded up to. See crate::Intrinsic.

fn overflow_box(&self) -> Option<Overflow>

If the widget lays its child out to constraints of its own, which the child may exceed, returns them. See crate::OverflowBox.

fn constraints_transform(&self) -> Option<ConstraintsTransform>

The box this widget gives its child as a function of the box it was offered, with the child laid out in it separately and the box then sized to what came back. None — the default — means the child shares this node’s layout, as everything ordinary does. See crate::ConstraintsTransformBox.

fn layout_builder(&self) -> Option<&dyn Fn(Size) -> Box<dyn Widget<Msg>>>

If the widget builds its content from its actual box, returns the size → widget factory. The content is built on the fly: no retained state and no overlay (like a virtualised list item).

fn scroll_overlay(&self) -> Option<&OverlayBuilder<Msg>>

If the widget draws something over its scroll region, returns the offset → overlay factory. See crate::ScrollOverlay.

fn scroll_axis(&self) -> Axis

SingleChildScrollView axis (or axes), for a scrollable container.

fn scroll_physics(&self) -> Option<ScrollPhysics>

The edge and fling behaviour of a scrollable container, when this widget wants one in particular. None — the usual answer — leaves the choice to the application, which defaults to what the platform does.

fn scrollbars(&self) -> Option<Scrollbars>

Whether this area draws a scrollbar, when it wants its own answer rather than the application’s. None — the default — follows the application, which follows the platform. See crate::Scrollbars.

fn thumb_visibility(&self) -> Option<bool>

Keep this area’s scrollbar on screen, instead of letting it fade away when the area stops moving (scrollbar.dart:214).

fn ime(&self) -> Ime

What the software keyboard should be, when this widget is the focused editable one.

fn overlay(&self) -> Option<(&dyn Widget<Msg>, Placement)>

If the widget is a portal, returns its floating content and its placement.

fn overlay_dismiss(&self) -> Option<Msg>

Message emitted when the scrim of a modal is clicked (dismissal), if any.

fn overlay_scrim(&self, _theme: &Theme) -> Option<Color>

The colour of the scrim behind this widget’s modal overlay, when it wants one in particular. None — the usual answer — leaves it to the scheme’s scrim role at the framework’s own opacity.

fn overlay_traps_focus(&self) -> bool

If true, this widget’s anchored overlay (a menu…) traps focus: Tab and the arrow keys cycle within its focusables while it is open (the keyboard pattern of menus). Modal (scrimmed) overlays already trap by default; a tooltip or an autocomplete list (focus stays on the field) do not. Default: false.

fn anim_target(&self) -> Option<f32>

Target of the widget’s own animated value (e.g. 1.0 for a switch that is on, 0.0 for off). The runtime drives the retained value towards this target and hands it back through Status::value. None = no animated value.

fn anim_transform(&self) -> Option<TransformValues>

Target transform of an animated one (Transform::animated): the runtime tweens the scales and the turn through anim_duration/anim_curve and hands the interpolated value back through Runtime::anim_transform, which the paint walk reads in place of the static transform_scale/transform_rotate. None = the transform does not move.

fn anim_duration(&self) -> f32

Duration (seconds) of the animated value’s transition (anim_target). Default: the framework’s standard duration.

fn anim_curve(&self) -> Curve

Easing curve of the animated value’s transition (anim_target). Default: linear.

fn opacity_group(&self) -> Option<f32>

If the widget is an opacity group, returns the (target) opacity [0,1] applied to its whole subtree as one: the paint walk wraps its primitives in a composited layer at that opacity — no double-blending where they overlap. None = not a group. Combined with anim_target, the opacity animates (a group fade).

fn anim_color(&self) -> Option<Color>

Target background colour of an animated background (Container::animated_color): the runtime tweens it (through anim_duration/anim_curve) and hands the interpolated value back in Status::anim_color. None = no animated colour.

fn anim_size(&self) -> Option<Size>

Target size of an animated size (Container::animated_size): the runtime tweens it (through anim_duration/anim_curve) and the interpolated size is injected at layout (see effective_style). None = fixed size.

fn anim_radius(&self) -> Option<BorderRadius>

Target corner radius of an animated radius (Container::animated_radius): the runtime tweens it and hands the interpolated value back in Status::anim_radius. None = fixed radius.

fn anim_padding(&self) -> Option<Insets>

Target padding of an animated padding (Container::animated_padding): the runtime tweens it and the interpolated padding is injected at layout (see effective_style). None = fixed padding.

fn anim_offset(&self) -> Option<(f32, f32)>

The pair of fractions this node’s offset rule is made of, animated: an alignment’s two fractions, or a slide’s. None — the default — leaves the rule reading the widget’s own numbers.

fn anim_pins(&self) -> Option<Positioning>

Target pins of an animated stack layer (crate::AnimatedPositioned): the runtime tweens them and the interpolated pins are read where the stack lays its layers out. None — the default — leaves Widget::positioned alone.

fn anim_fractions(&self) -> Option<(Option<f32>, Option<f32>)>

Target fractions of an animated share of the parent (FractionallySizedBox::animated), as (width factor, height factor): the runtime tweens them and the interpolated pair is injected at layout (see effective_style), like the size and the padding. None = fixed factors.

fn anim_text_style(&self) -> Option<TextStyle>

Target text style an animated subtree is heading for (AnimatedDefaultTextStyle). None = the subtree inherits whatever it inherits.

fn alignment_geometry(&self) -> Option<AlignmentGeometry>

Alignment of the single child within the box: the walk offsets the child through the free space according to the alignment’s fractions, resolved against the reading direction (physical or directional — see frus_core::AlignmentGeometry). Being continuous, a Tween<Alignment> read in view() slides the child. None = default flex placement.

fn transform_translate(&self) -> Option<(f32, f32)>

Paint offset (dx, dy) applied to the widget’s whole subtree: the render and the hit-test are offset without touching layout (siblings do not move, the child may overflow its box). Continuous → a Tween read in view() slides the subtree. None = no offset. See crate::Transform.

fn translate_fraction(&self) -> Option<(f32, f32)>

Paint offset as a fraction of the child’s own size (fx, fy): (0.5, 0.0) slides the subtree half its own width to the right. Added to Widget::transform_translate, and offsetting the render and the hit-test the same way, without touching layout. None = no offset.

fn transform_scale(&self) -> Option<(f32, f32, Alignment)>

Paint scaling (sx, sy, pivot) of the whole subtree: the render and the hit-test are scaled — per axis — around the pivot (a frus_core::Alignment within the box), without touching layout. Stays axis-aligned (a scaled rect is still a rect). None = no scaling. See crate::Transform.

fn transform_rotate(&self) -> Option<(f32, Alignment)>

Paint rotation (angle, pivot) of the whole subtree: the subtree is painted rotated by angle radians (clockwise) around the pivot (a frus_core::Alignment within the box), without touching layout. The render goes through a rotated composited layer; the hit-test counter-rotates the point. None = no rotation. See crate::Transform.

fn clip_shape(&self) -> Option<ClipShape>

Shape clip of the whole subtree: the paint walk wraps its primitives in a composited layer whose frus_core::ClipShape (rounded corners, ellipse) modulates the alpha — whatever falls outside the shape is erased, edges antialiased. None = no shape clip. See crate::ClipRRect, crate::ClipOval.

fn style_themed(&self, _theme: &Theme) -> Style

The widget’s style once the theme has had its say — the layout half of the caller ?? theme ?? framework chain.

fn theme_override(&self, _inherited: &Theme) -> Option<Box<Theme>>

The theme this widget imposes on itself and its subtree, given the one it inherits. None — the default — means “whatever came down from above”, which is what every widget but crate::Themed answers.

fn media_override(&self, _inherited: MediaQuery) -> Option<MediaQuery>

The surface this widget imposes on itself and its subtree, given the one it inherits. None — the default — means “whatever came down from above”, which is what every widget but MediaScope answers.

fn scaffold_override(&self) -> Option<ScaffoldInfo>

The shell this widget imposes on its subtree: what a Scaffold knows about itself and its slots do not.

fn build_themed(&self, _theme: &Theme)

Builds this widget’s subtree from the ambient theme, for the widgets that defer that decision — see ThemeBuilder. Does nothing by default, which is what all but a handful of widgets want.

fn build_in(&self, _id: WidgetId, _runtime: &Runtime, theme: &Theme)

Self::build_themed, for the few widgets that also need who they are and what the frame remembers to compose their subtree. An AnimatedSwitcher keeps what it is letting go of in the runtime, under its own identity, and that is reachable nowhere else before its children are read.

fn expand(&self, _id: WidgetId, _runtime: &Runtime, _theme: &Theme)

Builds what this node stands for, before anything else is asked of it.

fn switches(&self) -> bool

Whether this node is an AnimatedSwitcher. An identity is a position, so a switcher and the widget that comes to stand where it stood have the same one: this is how the runtime tells the switcher still being there from its having gone, and forgets what it kept for it.

fn system_ui_style(&self) -> Option<SystemUiOverlayStyle>

What the system bars over this widget should look like — see AnnotatedRegion. None for every widget but that one; a transparent wrapper forwards it, or a keyed region would say nothing.

fn ink(&self, _theme: &Theme) -> Option<InkStyle>

If the widget takes ink — the splash a tap leaves on a material surface — the shape and colour to splash in. None = no ink, which is the default: a widget has to ask.

fn foreground(&self, _theme: &Theme) -> Option<BoxDecoration>

A decoration painted over this widget’s children rather than behind them: the reference’s foregroundDecoration.

fn layer_filter(&self, _cx: FilterContext) -> Option<LayerFilter>

The pixel effects this widget applies to its whole subtree: a blur, a colour transform, a mask, or a filter over what is painted underneath. The paint walk drains the subtree into a composited layer and hands the filter to the renderer, exactly as it does for an opacity group or a shape clip.

fn backdrop_group(&self) -> bool

true when this widget is a backdrop group: the backdrops below it that ask to be shared are filtered once between them. See crate::BackdropGroup.

fn text_baseline(&self, _theme: &Theme) -> Option<f32>

The widget’s own text baseline: the distance from the top of its box down to the line its letters sit on. None — the default — means this widget has no text of its own, and whatever is inside it answers instead.

fn ignores_baseline(&self) -> bool

true when this subtree should be left out of a parent’s baseline alignment: it has a baseline, and the parent is to pretend it does not. An icon beside a label, where the label is what the row should line up on. See crate::IgnoreBaseline.

fn fill_axes(&self, _theme: &Theme) -> FillAxes

The axes this widget asks to fill: on each, it takes the room the parent leaves it rather than shrink-wrapping its children. FillAxes::NONE means shrink-wrap on both.

fn main_axis_floor(&self, _theme: &Theme) -> Option<f32>

The width below which this widget must not be squeezed when its parent runs horizontally — a line of text that would rather run past the end of a row than be folded into a column of single words. None means squeeze freely.

fn tile_shape(&self) -> Option<f32>

If this container gives all of its children the shape of a tile, the width / height ratio to impose on each of them. None = each child keeps its own shape.

fn positioned(&self) -> Option<Positioning>

If this is a layer pinned against its crate::Stack’s edges (crate::Positioned), what it pins. None = an ordinary layer, sized and placed by the stack’s own fit and alignment.

fn stack_loose(&self) -> bool

Whether this stack sizes its unpinned layers loosely — asking each what it would like to be — rather than handing each of them the whole box. See crate::StackFit. Meaningless unless Widget::stack is true.

fn stack_visible(&self) -> Option<usize>

Which layer of this stack is shown: the one at that index paints and takes input, and every other one is laid out and then silenced — not drawn, not clickable, not read out. None, the default, shows all of them.

fn keep_visible(&self, _size: Size, _theme: &Theme) -> Option<KeepVisible>

The box this widget asks the scroll region around it to keep in view, in its own coordinates, with a key naming which box it is.

fn scroll_reverse(&self) -> bool

Whether this scrollable runs from the far end (crate::SingleChildScrollView::reverse): the content is anchored to the end of the viewport and offsets are counted from there. Meaningless unless Widget::scroll_content is Some.

fn scroll_padding(&self) -> Insets

The insets a scrollable area puts around its content, inside the viewport.

fn baseline_target(&self) -> Option<f32>

If the widget positions its child by the child’s baseline (crate::Baseline), the distance from the top of this box at which that baseline should land. None = not a baseline box.

fn clip_path(&self) -> Option<&Path>

If the widget clips its child to an arbitrary path (ClipPath), returns the path in local coordinates (origin at the box’s top-left corner). The walk offsets it to the screen and wraps it in a layer whose mask (the path) erases the outside. Takes priority over Widget::clip_shape. None = no path clip. See crate::ClipPath.

fn dismissible(&self) -> Option<DismissSpec>

If the widget is a dismissible item (crate::Dismissible), its configuration for this frame. The shell gives a mostly-sideways drag on it to the dismissal and a mostly-up-and-down one to the enclosing scrollable. None = not dismissible.

fn on_dismissed(&self, _direction: DismissDirection) -> Option<Msg>

The message a dismissed item dispatches, once it has flown out and its gap has closed. None = the swipe is shown but removes nothing.

fn sheet(&self) -> Option<&SheetSpec>

If the widget is the moving panel of a crate::DraggableScrollableSheet, its configuration for this frame. The layout makes it as tall as the retained height, and the shell shares a finger on it between the sheet and the scroll areas inside. None = not a sheet.

fn on_sheet_dismissed(&self) -> Option<Msg>

The message a sheet dispatches once it has been lowered to nothing. None = it cannot be dismissed, or says nothing when it is.

fn refresh(&self) -> Option<RefreshSpec>

If the widget is a refresh area (crate::RefreshIndicator), its configuration for this frame. Any scrollable inside it routes the movement its physics refuses at the top edge into the pull, instead of into the overscroll glow. None = not a refresh area.

fn on_refresh(&self) -> Option<Msg>

The message a refresh area dispatches when an armed pull is released. None = the pull is shown but asks for nothing, which is what an area still waiting for its on_refresh looks like.

fn barrier(&self) -> Option<ModalBarrier>

What the widget withholds from the frame on behalf of its whole subtree: input targets, primitives, accessibility nodes. The walk visits the subtree normally and then discards whatever it added to the selected registries, so a target registered deep inside is caught just as surely as one at the top. None = nothing withheld (the default). See crate::ModalBarrier, crate::IgnorePointer, crate::AbsorbPointer, crate::Visibility, crate::ExcludeSemantics.

fn interactive(&self) -> Option<(f32, f32)>

If the widget is an interactive viewport (InteractiveViewer), returns its scale bounds (min, max). The paint walk renders its child in a transformed layer (retained scale + translation, clipped to the viewport); the shell routes drag → pan and wheel/pinch → zoom. None = not an interactive viewport. See crate::InteractiveViewer.

fn fitted(&self) -> Option<BoxFit>

If the widget fits its child to its box (FittedBox), returns the frus_core::BoxFit: the walk measures the child at its natural size, scales it according to the fit and centres it (composited layer, hit-test through M⁻¹). None = not a fitter. See crate::FittedBox.

fn rotated_quarter_turns(&self) -> Option<i32>

If the widget rotates its child by quarter turns (RotatedBox), returns the number of quarters. Unlike Transform, this affects layout: the box swaps its dimensions for an odd number. None = not a RotatedBox. See crate::RotatedBox.

fn navigator(&self) -> Option<(f32, bool)>

If the widget is a screen navigator, returns (progress, push?). Its children ([screen] or [outgoing, incoming]) are rendered full-window with a sliding transition.

fn navigator_clips(&self) -> bool

Whether a navigator clips its pages to its own box. true, which is the reference’s default (Clip.hardEdge) and the only sane one: a screen sliding in comes from outside the box and has to stop at its edge.

fn navigator_retained(&self) -> usize

How many of a navigator’s first children are kept but not shown: the pages under the one on show. They are built, so what their components hold survives, and they are not laid out, drawn or given input. 0, the default, is a navigator that shows every page it holds.

fn on_long_press(&self) -> Option<Msg>

Message emitted by a long press (a press held ~500 ms without movement). The long press pre-empts the click: the release that follows does not emit on_click.

fn on_key(&self, _key: &Key) -> KeyResponse<Msg>

Key received while bubbling leaf→root: the focused widget gets it first, then each ancestor as long as the response is Ignored. (E.g. an OverlayPortal consumes Escape to close itself.)

fn measure(&self, _theme: &Theme) -> Option<MeasureFn<'_>>

Measure under constraints: for a widget whose size depends on the space offered (a paragraph that wraps…), returns the closure wired into taffy. None = size fixed by style(). Contract: must be Some if and only if Widget::measure_key is.

fn measure_key(&self, _theme: &Theme) -> Option<u64>

Fingerprint of the content Widget::measure depends on (text, style…), mixed into the relayout fingerprint: without it, two different contents with the same style would be conflated by the cache and would keep a stale geometry. Contract: Some if and only if measure() is.