Add flutter_web samples (#75)

web/charts/example/lib/legends/datum_legend_with_measures.dart

@@ -0,0 +1,146 @@
+// Copyright 2018 the Charts project authors. Please see the AUTHORS file
+// for details.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+/// Bar chart with example of a legend with customized position, justification,
+/// desired max rows, and padding. These options are shown as an example of how
+/// to use the customizations, they do not necessary have to be used together in
+/// this way. Choosing [end] as the position does not require the justification
+/// to also be [endDrawArea].
+// EXCLUDE_FROM_GALLERY_DOCS_START
+import 'dart:math';
+// EXCLUDE_FROM_GALLERY_DOCS_END
+import 'package:flutter_web/material.dart';
+import 'package:charts_flutter/flutter.dart' as charts;
+
+/// Example that shows how to build a datum legend that shows measure values.
+///
+/// Also shows the option to provide a custom measure formatter.
+class DatumLegendWithMeasures extends StatelessWidget {
+  final List<charts.Series> seriesList;
+  final bool animate;
+
+  DatumLegendWithMeasures(this.seriesList, {this.animate});
+
+  factory DatumLegendWithMeasures.withSampleData() {
+    return new DatumLegendWithMeasures(
+      _createSampleData(),
+      // Disable animations for image tests.
+      animate: false,
+    );
+  }
+
+  // EXCLUDE_FROM_GALLERY_DOCS_START
+  // This section is excluded from being copied to the gallery.
+  // It is used for creating random series data to demonstrate animation in
+  // the example app only.
+  factory DatumLegendWithMeasures.withRandomData() {
+    return new DatumLegendWithMeasures(_createRandomData());
+  }
+
+  /// Create random data.
+  static List<charts.Series<LinearSales, int>> _createRandomData() {
+    final random = new Random();
+
+    final data = [
+      new LinearSales(2014, random.nextInt(100)),
+      new LinearSales(2015, random.nextInt(100)),
+      new LinearSales(2016, random.nextInt(100)),
+      new LinearSales(2017, random.nextInt(100)),
+    ];
+
+    return [
+      new charts.Series<LinearSales, int>(
+        id: 'Sales',
+        domainFn: (LinearSales sales, _) => sales.year,
+        measureFn: (LinearSales sales, _) => sales.sales,
+        data: data,
+      )
+    ];
+  }
+  // EXCLUDE_FROM_GALLERY_DOCS_END
+
+  @override
+  Widget build(BuildContext context) {
+    return new charts.PieChart(
+      seriesList,
+      animate: animate,
+      // Add the legend behavior to the chart to turn on legends.
+      // This example shows how to optionally show measure and provide a custom
+      // formatter.
+      behaviors: [
+        // EXCLUDE_FROM_GALLERY_DOCS_START
+        // This section is excluded from being copied to the gallery.
+        // This is added in order to generate the image for the gallery to show
+        // an initial selection so that measure values are shown in the gallery.
+        new charts.InitialSelection(
+          selectedDataConfig: [
+            new charts.SeriesDatumConfig('Sales', 0),
+          ],
+        ),
+        // EXCLUDE_FROM_GALLERY_DOCS_END
+        new charts.DatumLegend(
+          // Positions for "start" and "end" will be left and right respectively
+          // for widgets with a build context that has directionality ltr.
+          // For rtl, "start" and "end" will be right and left respectively.
+          // Since this example has directionality of ltr, the legend is
+          // positioned on the right side of the chart.
+          position: charts.BehaviorPosition.end,
+          // By default, if the position of the chart is on the left or right of
+          // the chart, [horizontalFirst] is set to false. This means that the
+          // legend entries will grow as new rows first instead of a new column.
+          horizontalFirst: false,
+          // This defines the padding around each legend entry.
+          cellPadding: new EdgeInsets.only(right: 4.0, bottom: 4.0),
+          // Set [showMeasures] to true to display measures in series legend.
+          showMeasures: true,
+          // Configure the measure value to be shown by default in the legend.
+          legendDefaultMeasure: charts.LegendDefaultMeasure.firstValue,
+          // Optionally provide a measure formatter to format the measure value.
+          // If none is specified the value is formatted as a decimal.
+          measureFormatter: (num value) {
+            return value == null ? '-' : '${value}k';
+          },
+        ),
+      ],
+    );
+  }
+
+  /// Create series list with one series
+  static List<charts.Series<LinearSales, int>> _createSampleData() {
+    final data = [
+      new LinearSales(2014, 100),
+      new LinearSales(2015, 75),
+      new LinearSales(2016, 25),
+      new LinearSales(2017, 5),
+    ];
+
+    return [
+      new charts.Series<LinearSales, int>(
+        id: 'Sales',
+        domainFn: (LinearSales sales, _) => sales.year,
+        measureFn: (LinearSales sales, _) => sales.sales,
+        data: data,
+      )
+    ];
+  }
+}
+
+/// Sample linear data type.
+class LinearSales {
+  final int year;
+  final int sales;
+
+  LinearSales(this.year, this.sales);
+}