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@jsvision/datagrid / FooterBand

Class: FooterBand<T> ​

Documented in: Data Grid

Defined in: datagrid/src/footer-band.ts:62

A single-row band painting one panel's footer aggregate cells, aligned to their columns. Passive and non-focusable — it mirrors the body's geometry but never takes the keyboard.

Example ​

ts
import { signal } from '@jsvision/ui';
import { FooterBand } from '@jsvision/datagrid';

interface Row { qty: number }
const columns = [{ title: 'Qty', accessor: (r: Row) => String(r.qty), width: 6 }];
const columnIds = ['qty'];
const totals: Record<string, string> = { qty: '42' };
// Built by the grid per frozen/scrolling segment; a bespoke `cell` supplies each column's aggregate text:
const band = new FooterBand({
  columns,
  columnIds,
  autoWidths: () => [null],
  indent: signal(0),
  compact: false,
  widthTick: () => 0,
  cell: (id) => totals[id] ?? '',
});

Extends ​

  • View

Type Parameters ​

T ​

T

Constructors ​

Constructor ​

new FooterBand<T>(cfg): FooterBand<T>

Defined in: datagrid/src/footer-band.ts:75

Parameters ​

cfg ​

FooterBandConfig<T>

The column slice, geometry inputs, resize trigger, and the aggregate-cell accessor.

Returns ​

FooterBand<T>

Overrides ​

View.constructor

Properties ​

bounds ​

bounds: Rect

Defined in: ui/dist/view/view.d.ts:61

Parent-relative integer rect; written by the layout pass — read it in draw/hit-testing.

Inherited from ​

View.bounds

castsShadow ​

castsShadow: boolean

Defined in: ui/dist/view/view.d.ts:91

When true, the renderer paints a drop shadow on the cells just below and to the right of this view, in paint order (a later sibling's shadow falls over an earlier one). Default false. The Desktop sets it per window.

Inherited from ​

View.castsShadow

centered ​

centered: boolean

Defined in: ui/dist/view/view.d.ts:98

When true, the layout pass recentres this view within its parent after layout — origin = (parent - self) / 2 on both axes. Intended for absolutely-placed views (a modal dialog, a message box) whose size is fixed and whose origin would otherwise be placed by the caller. Default false; Dialog sets it when centered.

Inherited from ​

View.centered

focusable ​

focusable: boolean = false

Defined in: datagrid/src/footer-band.ts:63

Whether this view can receive keyboard focus. Effective focusability also requires the view to be visible and enabled with no hidden/disabled ancestor. Default false; the focus manager drives the state.focused flag.

Overrides ​

View.focusable

grabsFocus ​

grabsFocus: boolean

Defined in: ui/dist/view/view.d.ts:113

Whether a mouse-down that hits this view moves keyboard focus to it. Default true — the usual click-to-focus. Set false for a control that should act on a click without stealing focus from whatever is focused (e.g. a dialog Cancel button, or a toolbar/stepper button): the click still dispatches, but the previously-focused view keeps focus, so it never fires a focus-leave side effect such as a field's blur-validation. Independent of focusable — a grabsFocus: false view can still be reached by Tab and activated by Space.

Inherited from ​

View.grabsFocus

layout ​

readonly layout: Readonly<LayoutProps>

Defined in: ui/dist/view/view.d.ts:83

Layout props for this view (direction, size, padding, absolute placement, …) — read-only.

Change them with setLayout, which is the only writer. The field and every prop on it are closed, so neither view.layout = {…} nor view.layout.rect = {…} compiles, and neither does editing a solved rect a field at a time (view.layout.rect.x = 5). That is deliberate: a wholesale assignment silently drops every prop it omits and never reflows, and an in-place prop write reflows only if you remember to ask.

Read it freely — this is where a view's solved intent lives, and layout.rect is how an absolutely-placed view reports where it was put.

Inherited from ​

View.layout

postProcess ​

postProcess: boolean

Defined in: ui/dist/view/view.d.ts:117

Take part in the post-process sweep (after the focused view sees the event).

Inherited from ​

View.postProcess

preProcess ​

preProcess: boolean

Defined in: ui/dist/view/view.d.ts:115

Take part in the pre-process sweep (root→down, before the focused view sees the event).

Inherited from ​

View.preProcess

state ​

readonly state: ViewState

Defined in: ui/dist/view/view.d.ts:70

Draw-against flags. The object reference is fixed; individual fields mutate (e.g. focused).

Writing visible or disabled changes only what the next paint would draw — it does not ask for that paint. Follow such a write with invalidate (or invalidateLayout, which a visibility flip needs, since layout omits hidden views). A development build warns when a write goes unaccounted for.

Inherited from ​

View.state

Methods ​

accelerators() ​

accelerators(): readonly string[]

Defined in: ui/dist/view/view.d.ts:131

The Alt+hotkey accelerator characters (lowercase) this view claims in its focus scope, for duplicate-accelerator detection. The base returns none; accelerator-bearing widgets (Button/Label/CheckGroup/RadioGroup) override it to report their ~X~ hotkey(s).

Returns ​

readonly string[]

The claimed accelerator chars, or an empty list when the view claims none.

Inherited from ​

View.accelerators

bind() ​

bind<T>(reader, apply?, opts?): void

Defined in: ui/dist/view/view.d.ts:277

Bind a reactive value to a redraw. Creates an effect (owned by this view's scope) that reads reader() — subscribing to whatever signals it touches — runs the optional apply(value), then requests a frame: a repaint by default, or a reflow when { relayout: true }. It re-runs automatically whenever those signals change, and is disposed when the view unmounts.

Call it from onMount, not the constructor — the view's scope only exists once mounted, so a pre-mount bind throws rather than silently dropping the binding.

Type Parameters ​

T ​

T

Parameters ​

reader ​

() => T

Reads the reactive source; the signals it reads become dependencies.

apply? ​

(v) => void

Optional: apply the read value to the widget (e.g. store it in a field).

opts? ​

Pass { relayout: true } when the change affects layout, so it reflows instead of just repainting.

relayout? ​

boolean

Returns ​

void

Example ​

ts
import { View, signal, type DrawContext } from '@jsvision/ui';

const count = signal(0);

class StatusLine extends View {
  draw(ctx: DrawContext): void {
    ctx.text(0, 0, `${count()} pending`, ctx.color('statusBar'));
  }
}

const status = new StatusLine();
// In onMount, not the constructor: bind() needs the view's scope, which only exists once mounted.
status.onMount(() => {
  status.bind(() => count()); // repaint the status line whenever `count` changes
});

Inherited from ​

View.bind

derived() ​

protected derived<T>(fn): () => T

Defined in: ui/dist/view/view.d.ts:299

Create a stable derived accessor owned by this view's scope. The returned () => T keeps the same identity for the life of the view, so it is safe to build in the constructor and hand to child views before this view mounts. The backing computed is created lazily under the view's own scope, so it is always owned and disposed at unmount — unlike a bare computed() in the constructor, which would run before any scope exists, leak, and warn.

Reads behave sensibly across the lifecycle:

  • Before mount: evaluates fn() directly (correct current value, nothing persisted). Good for a pre-mount natural-size measure.
  • After mount: builds and memoizes a computed(fn) under the view's scope.
  • After an unmount→remount: the memo is keyed to the scope it was built under, so a remounted view (which gets a fresh scope) re-derives under the new scope instead of returning the previous mount's disposed, now-frozen computed — keeping a Show/For-remounted widget reactive.

Type Parameters ​

T ​

T

Parameters ​

fn ​

() => T

The derivation (pure; the signals it reads become the computed's dependencies).

Returns ​

A stable accessor; call it to read the derived value.

() => T

Inherited from ​

View.derived

desiredCaret() ​

desiredCaret(): Point | null

Defined in: ui/dist/view/view.d.ts:211

Where this view wants the hardware text cursor, in view-local cells, or null for no cursor (the default — most views never show one). A focused text input overrides this to place the caret at the edit position; the event loop reads it after each frame, converts it to an absolute cell, and moves the terminal cursor there.

Returns ​

Point | null

The view-local caret point (0-based, relative to this view's origin), or null.

Inherited from ​

View.desiredCaret

draw() ​

draw(ctx): void

Defined in: datagrid/src/footer-band.ts:107

Paint this view through a clipped, view-local context. Every widget overrides this to draw itself; the base declares it abstract so a subclass must supply it.

Parameters ​

ctx ​

DrawContext

The view-local, auto-clipped paint API (see DrawContext).

Returns ​

void

Overrides ​

View.draw

focusSignal() ​

focusSignal(): Signal<void>

Defined in: ui/dist/view/view.d.ts:168

Subscribe to this view's focus changes. Reading the returned signal inside a bind/effect re-runs that effect whenever this view gains or loses focus — including from another view (e.g. a Label repainting when the control it labels is focused). The signal notifies on every poke even without a value change. Lazy: the backing signal is created on first call.

Returns ​

Signal<void>

A signal that ticks whenever this view gains or loses focus.

Example ​

ts
import { View, Button, type DrawContext } from '@jsvision/ui';

// A caption that highlights while the control it labels holds focus.
class Caption extends View {
  constructor(
    private readonly text: string,
    private readonly target: View,
  ) {
    super();
    // Reading the target's focus signal inside bind() ties this view's repaint to the target's
    // focus flips — a view can observe focus it does not own.
    this.onMount(() => this.bind(() => this.target.focusSignal()()));
  }

  draw(ctx: DrawContext): void {
    ctx.text(0, 0, this.text, ctx.color(this.target.state.focused ? 'labelSelected' : 'label'));
  }
}

const ok = new Button('~O~K');
const caption = new Caption('Confirm:', ok);

Inherited from ​

View.focusSignal

invalidate() ​

invalidate(): void

Defined in: ui/dist/view/view.d.ts:213

Request a repaint of this view. A no-op before the view is mounted (the first frame paints everything).

Returns ​

void

Inherited from ​

View.invalidate

invalidateLayout() ​

invalidateLayout(): void

Defined in: ui/dist/view/view.d.ts:215

Request a reflow (re-run layout, then repaint). Use this when a change affects size/position, not just pixels.

Returns ​

void

Inherited from ​

View.invalidateLayout

measure()? ​

optional measure(available): Size2D

Defined in: ui/dist/view/view.d.ts:85

Optional intrinsic-size hook for auto sizing — return the size this view wants for available.

Parameters ​

available ​

Size2D

Returns ​

Size2D

Inherited from ​

View.measure

onCleanup() ​

onCleanup(fn): void

Defined in: ui/dist/view/view.d.ts:315

Register a teardown callback that runs once when this view unmounts. Requires a mounted view — so call it from within onMount. Use it to release anything the view acquired (a timer, an external subscription).

Parameters ​

fn ​

() => void

The teardown callback.

Returns ​

void

Inherited from ​

View.onCleanup

onEvent() ​

onEvent(_ev): void

Defined in: ui/dist/view/view.d.ts:195

Handle an input event — a no-op by default. The event loop wraps each event in a DispatchEvent envelope and routes it to the views; override this to react to keys/mouse and set ev.handled = true to consume the event so it does not propagate further.

Parameters ​

_ev ​

DispatchEvent

The dispatch envelope (the wrapped event plus the mutable handled flag).

Returns ​

void

Inherited from ​

View.onEvent

onMount() ​

onMount(fn): void

Defined in: ui/dist/view/view.d.ts:307

Register a callback to run once when the view becomes live (after its first layout gives it bounds). This is where to call bind, since the view's reactive scope exists by then. Registering after the view is already live runs the callback immediately.

Parameters ​

fn ​

() => void

Post-mount setup.

Returns ​

void

Inherited from ​

View.onMount

selectByClick()? ​

optional selectByClick(): void

Defined in: ui/dist/view/view.d.ts:202

Optional "select + raise on click" hook. Left undefined on the base, so a plain view is not a select/raise target. A container that owns z-order (a Window) overrides it to select and raise itself. The hit-test invokes the first ancestor that defines this — before delivering the mouse-down — so a click always raises the window even if the interior also consumes the click.

Returns ​

void

Inherited from ​

View.selectByClick

setLayout() ​

setLayout(patch): void

Defined in: ui/dist/view/view.d.ts:246

Change some of this view's layout props and request a reflow — the only way to write layout. Props the patch does not name are kept, and the reflow happens for you.

The merge is shallow, deliberately: size and rect are replaced whole rather than merged field-by-field. That is what makes a variant swap correct — going from {kind:'fixed',cells:1} to {kind:'fr',weight:1} must not leave a stale cells behind. The cost is that per-side padding cannot be patched one side at a time; pass the whole padding value.

Two behaviours worth knowing:

  • An explicit undefined resets that prop to its layout default. setLayout({ size: undefined }) makes the view auto-sized again, and setLayout({ position: 'flow' }) puts an absolutely-placed view back in the flow (its now-unused rect is simply ignored).
  • Do not call it in a constructor of a class that subclasses may extend. A base constructor body runs before a subclass's override readonly layout = {…} field initializer, and that initializer installs a fresh object, so the call would be erased. Call it after construction, or from onMount.

Reflowing an unmounted view is a no-op, so calling it before mount is safe.

Parameters ​

patch ​

Partial<LayoutProps>

The layout props to change; anything omitted is preserved.

Returns ​

void

Example ​

ts
import { Group } from '@jsvision/ui';

const panel = new Group();
panel.setLayout({ direction: 'col', padding: 1 });
// Later — `direction` and `padding` survive; once `panel` is mounted this also reflows:
panel.setLayout({ size: { kind: 'fr', weight: 1 } });

Inherited from ​

View.setLayout