如何在波动图内单击时显示项目的数据值

Question

我在我的一个项目中使用了Charts_flutter库，我想在单击每个条形图项目时显示数据值。可能吗？

var data = [
  new ClicksPerYear('2016', 12, Colors.red),
  new ClicksPerYear('2017', 42, Colors.blue),
  new ClicksPerYear('2018', counter, Colors.green),
];

var series = [
  new charts.Series(
    id: 'Clicks',
    data: data,
    domainFn: (ClicksPerYear clickData, _) => clickData.year,
    measureFn: (ClicksPerYear clickData, _) => clickData.clicks,
    colorFn: (ClicksPerYear clickData, _) => clickData.color,
  )
];
var barChart = new charts.BarChart(
      series,
      animate: true,
);

Answer 1

从 Github 问题中找到了解决方案

https://github.com/google/charts/issues/58

要获取该值，请使用 SelectionModelConfig.changedListener。

扩展 CircleSymbolRenderer（用于 LinePointHighlighter.symbolRenderer）并覆盖 Paint 方法。在内部，您可以相对于所选点绘制自定义对象。

也许将来作者会让这更容易，但现在您可以使用此方法以您需要的任何方式修改所选点的渲染过程（使用 ChartCanvas 方法）

import 'dart:math';

import 'package:flutter/material.dart';
import 'package:charts_flutter/flutter.dart';
import 'package:charts_flutter/src/text_element.dart';
import 'package:charts_flutter/src/text_style.dart' as style;

class Chart extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return LineChart(
      _createSampleData(),
      behaviors: [
        LinePointHighlighter(
          symbolRenderer: CustomCircleSymbolRenderer()
        )
      ],
      selectionModels: [
        SelectionModelConfig(
          changedListener: (SelectionModel model) {
            if(model.hasDatumSelection)
              print(model.selectedSeries[0].measureFn(model.selectedDatum[0].index));
          }
        )
      ],
    );
  }

  List<Series<LinearSales, int>> _createSampleData() {
    final data = [
      new LinearSales(0, 5),
      new LinearSales(1, 25),
      new LinearSales(2, 100),
      new LinearSales(3, 75),
    ];
    return [
      new Series<LinearSales, int>(
        id: 'Sales',
        colorFn: (_, __) => MaterialPalette.blue.shadeDefault,
        domainFn: (LinearSales sales, _) => sales.year,
        measureFn: (LinearSales sales, _) => sales.sales,
        data: data,
      )
    ];
  }
}

class CustomCircleSymbolRenderer extends CircleSymbolRenderer {
  @override
  void paint(ChartCanvas canvas, Rectangle<num> bounds, {List<int> dashPattern, Color fillColor, Color strokeColor, double strokeWidthPx}) {
    super.paint(canvas, bounds, dashPattern: dashPattern, fillColor: fillColor, strokeColor: strokeColor, strokeWidthPx: strokeWidthPx);
    canvas.drawRect(
      Rectangle(bounds.left - 5, bounds.top - 30, bounds.width + 10, bounds.height + 10),
      fill: Color.white
    );
    var textStyle = style.TextStyle();
    textStyle.color = Color.black;
    textStyle.fontSize = 15;
    canvas.drawText(
      TextElement("1", style: textStyle),
        (bounds.left).round(),
        (bounds.top - 28).round()
    );
  }
}
class LinearSales {
  final int year;
  final int sales;
  LinearSales(this.year, this.sales);
}

Answer 2

看起来为 Charts_flutter 提供的示例所做的事情与您想要做的事情非常相似。

具体参见build方法内部参考_onSelectionChanged方法：

GitHub 上的 Charts_flutter 选择示例