Text area (built-in)

Authoring

use day::prelude::*;

let body = Signal::new(String::new());
text_area(body)
    .placeholder("Write a message…")
    .min_lines(3)     // never shorter than 3 lines
    .max_lines(8)     // grows to 8, then scrolls internally
    .id("compose")

text_area(text) binds a Signal<String> two-way: keystrokes write the signal, and setting the signal replaces the editor’s text (echo-guarded, so a programmatic set that matches the last typed value doesn’t loop). .placeholder(_) sets the empty-state prompt (evaluated once, not reactive). The height auto-grows with content between .min_lines(_) (default 1) and .max_lines(_) (default 0 = unbounded, never scrolls); a non-zero max is floored to min. TextArea implements Piece, so .id()/.a11y()/.frame() chain via Decorate.

Attributes

Three attributes control the native editor, each a reactive bool (a constant or a signal/closure) that updates live:

text_area(report)
    .editable(false)      // read-only (default true)
    .selectable(true)     // still copyable (default true)
    .spellcheck(false)    // no spell-correction squiggles (default true)

• .editable(v) — false makes the editor read-only.
• .selectable(v) — whether the text can be selected and copied (useful with .editable(false) for a read-only-but-copyable display).
• .spellcheck(v) — the spell-check / autocorrect highlighting.

Native support varies; a toolkit that can’t honor an attribute answers the matching capability with Support::Unsupported, so an app can gray out a control that would do nothing. Emulated means the attribute IS honored, just not by one native property, so the test to gray a control is capability(…) == Support::Unsupported, not != Support::Native (the showcase’s Text Areas page gates its three toggles that way):

GTK’s GtkTextView is always selectable (no toggle), and neither GTK nor Qt ships a built-in spell-checker (that needs libspelling/gspell or Hunspell).

XAML honors editable and spell-check with the plain TextBox properties IsReadOnly and IsSpellCheckEnabled. Selection is the odd one out: IsTextSelectionEnabled is a TextBlock / RichTextBlock property and TextBox carries no equivalent, so .selectable(false) is EMULATED: the shim collapses each selection as SelectionChanged reports it and suppresses the context menu, which is the other route to Copy / Select All. The ArkUI editor supports all three natively but its shim doesn’t expose the setters yet, a documented follow-up; until then it reports Unsupported for all three and ignores the props.

It is the multi-line sibling of text_field (docs/forms.md): a field is one line and submits on Return; a text area keeps newlines. Both raise the soft keyboard through the focus system (docs/focus.md), and keyboard avoidance (the focused editor scrolling clear of the keyboard) applies to both.

Per-backend native realization

Each backend keeps the (min_lines, max_lines) band and grows its measure height in a line band. Text changes report through Event::TextChanged(String); programmatic sync (TextAreaPatch::SetText) is echo-guarded per backend, and the attribute patches (SetEditable/SetSelectable/SetSpellCheck) apply the native property. The Qt and XAML renderers carry C++ shims in the matching -sys crate (shim-textarea.cpp: Qt adds day_textarea_set_attrs/set_read_only/set_selectable; XAML adds day_textarea_xaml_set_editable/set_selectable/set_spellcheck, applied at build as well as on patch so an editor that starts read-only comes up that way); Android’s DayTextArea.java rides the framework shim (its applyAttrs maps editable→InputType/keyListener, selectable→setTextIsSelectable, spell-check→TYPE_TEXT_FLAG_NO_SUGGESTIONS).

Verification

The Day-Matrix app’s composer (a standalone Day app) is the shipped consumer. 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.

Follow-ups

• XAML + ArkUI attribute setters: TextBox/ARKUI_NODE_TEXT_AREA support editable/selectable/ spell-check natively, but their shims don’t expose the setters yet; they report Unsupported and ignore the props for now.
• Styled text is a different control: day-piece-texteditor edits a whole StyledText — the document labels render and .markdown() produces — in each platform’s rich-text view (docs/texteditor.md). text_area stays the plain-text one.
• Reactive placeholder; a character/line counter affordance.