Spline area Chart in Flutter Cartesian Charts (SfCartesianChart)

21 May 2021 / 9 minutes to read

To render a spline area chart, create an instance of SplineAreaSeries, and add it to the series collection property of SfCartesianChart. The following properties can be used to customize the appearance of spline area chart:

• color - changes the color of the series.
• opacity - controls the transparency of the chart series.
• width - changes the stroke width of the series.

dart

@override
    Widget build(BuildContext context) {
        return Scaffold(
            body: Center(
                child: Container(
                    child: SfCartesianChart(
                        primaryXAxis: DateTimeAxis(),
                        series: <ChartSeries>[
                            SplineAreaSeries<SalesData, DateTime>(
                                dataSource: chartData,
                                xValueMapper: (SalesData sales, _) => sales.year,
                                yValueMapper: (SalesData sales, _) => sales.sales
                            ),
                            SplineAreaSeries<SalesData, DateTime>(
                                dataSource: chartData1,
                                xValueMapper: (SalesData sales, _) => sales.year,
                                yValueMapper: (SalesData sales, _) => sales.sales
                            ),
                        ]
                    )
                )
            )
        );
    }

Dashed spline area

The dashArray property of the SplineAreaSeries is used to render spline area series with dashes. Odd value is considered as rendering size and even value is considered as gap.

dart

@override
    Widget build(BuildContext context) {
        return Scaffold(
            body: Center(
                child: Container(
                    child: SfCartesianChart(
                        primaryXAxis: DateTimeAxis(),
                        series: <ChartSeries>[
                            SplineAreaSeries<SalesData, DateTime>(
                                dataSource: chartData,
                                dashArray: <double>[5, 5],
                                xValueMapper: (SalesData sales, _) => sales.year,
                                yValueMapper: (SalesData sales, _) => sales.sales
                            )
                        ]
                    )
                )
            )
        );
    }

Spline area rendering types

The splineType allows you to change the spline area curve in series. The following types can be used in SplineAreaSeries:

• natural
• monotonic
• cardinal
• clamped

By default, the value of splineType is natural.

The following code sample demonstrates how to set the splineType value to cardinal. When you set the cardinal type, you can specify the desired line tension of the cardinal spline using the cardinalSplineTension property. The value of this property ranges from 0 to 1.

dart

@override
    Widget build(BuildContext context) {
        return Scaffold(
            body: Center(
                child: Container(
                    child: SfCartesianChart(
                        primaryXAxis: DateTimeAxis(),
                        series: <ChartSeries>[
                            SplineAreaSeries<SalesData, DateTime>(
                                dataSource: chartData,
                                splineType: SplineType.cardinal,
                                cardinalSplineTension: 0.9,
                                xValueMapper: (SalesData sales, _) => sales.year,
                                yValueMapper: (SalesData sales, _) => sales.sales
                            )
                        ]
                    )
                )
            )
        );
    }