tessera_flutter #

Flutter widgets for the tessera pivot-table engine: an expandable cube grid, drag-and-drop axis and aggregate editors, picker dialogs, and localizations for fourteen languages.

Status: early development. Everything works end to end and is covered by widget tests, but the API is still moving and nothing is published to pub.flutter-io.cn yet.

This package re-exports package:tessera/tessera.dart, so a single import gives you both the engine and the widgets. Read the engine's README for the concepts (data sources, schema inference, fact tables, cube specs).

Widgets #

Usage #

import 'package:tessera_flutter/tessera_flutter.dart';

final controller = CubeController(Cube(facts: facts, spec: spec));

Column(
  children: [
    AxisEditor(controller: controller, side: AxisSide.rows),
    AxisEditor(controller: controller, side: AxisSide.columns),
    AggregateEditor(controller: controller),
    Expanded(
      child: CubeView(
        controller: controller,
        // one value column per aggregate under each column entry;
        // omit to show every aggregate of the spec
        aggregates: [Aggregate.sum(const Measure('total')), Aggregate.count],
        formatCell: (cell, value) => myNumberFormat.format(value),
      ),
    ),
  ],
)

Expand and collapse groups with the +/− icons; tap a dimension name to sort that level by value, or an aggregate name under a column to sort the rows by that value column. A level without a sort of its own follows the level above (AxisDimension.sort == null), so a deeper level's name cycles through the opposite direction, the same direction, and inheriting again. Every dimension name also has a menu (its ▾ button, a long press, or a secondary click) with the sort direction, "same order as the level above", and "expand all" / "collapse all" for that level. expansionLimit with confirmExpansion / confirmLevelExpansion ask before an expansion would add too many rows or columns.

Tapping a data cell makes it the current cell: it is outlined, its row and column headers are tinted, and controller.selection holds its CellAddress (row and column paths, so it survives sorting and expanding other groups). controller.currentCell resolves it against the current layout — the CubeCell with its facts and aggregates, or null when the cell is not visible — which is what an app charts or drills into. The view takes focus on tap; the arrow keys, Home/End (first/last column, with Ctrl first/last row) and Page Up/Down (on the number block too) move the current cell (scrolled into view), Enter or Space toggles its row group and Escape clears it. selectable: false turns this off; focusNode and autofocus work as on a TextField. CubeTheme.selectionColor is the outline colour.

Localization #

MaterialApp(
  localizationsDelegates: const [
    TesseraLocalizations.delegate,
    ...GlobalMaterialLocalizations.delegates,
  ],
  supportedLocales: TesseraLocalizations.supportedLocales,
)

Without a delegate the widgets fall back to English. To force a language (or supply your own TesseraStrings subclass), wrap the app in a TesseraLocalizationsScope.

Example app #

example/ is one Flutter app with a launcher page listing several examples (example/lib/examples.dart). Simple pivot (example/lib/simple/) loads example/assets/sales.csv (1 000 generated sales rows with deliberately missing values, hierarchical dimensions and orphan values — see example/tool/gen_sales_csv.dart) and lets you configure everything interactively: the inferred schema (include, type, label, date format, number syntax per column), the axes (drag-and-drop), the aggregates, the language, and the cube itself. Public datasets (example/lib/datasets/) downloads real-world CSV files of up to ~70 MB through a custom HttpCsvDataSource (example/lib/common/http_csv_data_source.dart) — a worked example of implementing DataSource, with early-cancelled prefix reads, a download cache and Content-Length-based progress.

cd example && flutter run

Contributing #

Issues and pull requests are welcome at https://github.com/nagylzs/tessera. Run flutter analyze and flutter test before submitting.

Author #

László Zsolt Nagy nagylzs@gmail.com

License #

MIT — see LICENSE.