Picker (built-in)

Status: implemented as a built-in piece (kinds::PICKER; moved in from the satellite day-piece-picker 2026-07). One API, three SwiftUI-style stylings, each a distinct native control per toolkit, bound two-way to a selection. In day::prelude::*, with no dependency to add.

Authoring

use day::prelude::*;

let size = Signal::new(1usize);
picker(["Small", "Medium", "Large"], size).segmented().id("size")   // horizontal one-of-N
picker(colors, color).menu()                                         // dropdown / pop-up
picker(plans, plan).inline()                                         // vertical radio group

picker(options, selected) takes fixed options (impl IntoIterator<Item: Into<String>>) and a Signal<usize> bound two-way (the widget writes the selected index back; setting the signal moves the widget). Default style is .menu(); .segmented() / .inline() / .style(PickerStyle) switch it. Picker implements Piece, so .id()/.a11y()/.frame() chain via Decorate.

Per-backend native realization

style	AppKit	UIKit	GTK	Qt	Android	XAML	ArkUI
Menu	`NSPopUpButton`	`UIButton`+`UIMenu` pull-down	`GtkDropDown`	`QComboBox`	`Spinner`	`ComboBox`	`TextPicker` wheel
Segmented	`NSSegmentedControl`	`UISegmentedControl`	`.linked` grouped `GtkToggleButton`s	checkable `QPushButton`s in a `QButtonGroup`	button-row `LinearLayout` (dim unselected)	horizontal `RadioButton` `StackPanel`	`TextPicker` wheel
Inline	vertical `NSStackView` of radio `NSButton`s	checkmark-row `UIStackView`	grouped `GtkCheckButton`s (radio)	`QRadioButton`s in a `QButtonGroup`	`RadioGroup`	vertical `RadioButton` `StackPanel`	`TextPicker` wheel

HarmonyOS has no segmented control, so ArkUI renders every style as the native ARKUI_NODE_TEXT_PICKER wheel, the platform’s option-selection idiom. The Qt and XAML renderers each carry a C++ shim in the matching -sys crate (toolkits/day-qt-sys/src/shim-picker.cpp, toolkits/day-xaml-sys/src/shim-picker.cpp); the XAML shim boxes its XAML element into a Day handle through the day_xaml_box/day_xaml_unbox seam. Android’s Java factory (toolkits/day-android/java/dev/daybrite/day/piece/picker/DayPicker.java) rides the framework shim. All backends report selection through Event::SelectionChanged(i64); programmatic selection is echo-guarded per backend so it never loops.

Verification

The showcase Controls page (controls.rs pickers_section) shows all three styles bound to ONE shared selection signal, each with a live value label. Rendering and correct initial selection are screenshot-verified on all 5 local targets (AppKit, GTK, Qt, iOS-sim, Android-emu); a mock-backend test (crates/day-pieces/tests/mock_e2e.rs picker_and_text_area_are_built_in) asserts the two-way binding round-trips. The walkthrough drives select through each styling and asserts the readouts follow.

Follow-ups

Reactive options (currently fixed at build; only selected patches), mirroring the combobox’s Items.
Disabled/enabled state; per-option a11y labels.