How to increase the size of the tapped segment in the pie chart?

In this article, we explain how to increase the size of the tapped segment in the pie chart using the Flutter Cartesian chart.

The SfCircularChart widget have the onPointTap callback in the series and pointRadiusMapper property in the series, using these you can increase the size of the tapped segment.

Here onPointTap callback gets trigged when tapping on the segment, in this call back you can get the pointIndex, seriesIndex, viewportPointIndex, and dataPoints of the tapped segment. Then pointRadiusMapper is used to map the radius for the point from the data source, using this we can render each segment with different radius.

In the following steps explain how to increase the size of the tapped segment in the PieSeries.

Step 1: Initialize the variable chartData which stores the data source, pointIndex stores the index value of the tapped segment and radius which is mapped to the respected tapped slice. Then assign the value at the initState.

int? pointIndex;
late String radius;
late List<SampleData> chartData;
 
@override
void initState() {
  radius = '140';
  chartData = <SampleData>[
    SampleData('1', 120),
    SampleData('2', 40),
    SampleData('3', 10),
    SampleData('4', 10),
    SampleData('5', 10),
    SampleData('6', 6),
    SampleData('7', 4),
    SampleData('8', 1),
    SampleData('9', 60),
  ];
  super.initState();
}
 
class SampleData {
  SampleData(this.x, this.y);
  final String x;
  final num y;
}

Step 2: Now create the SfCircularChart widget with the PieSeries and assign the chartData to the dataSource property and map the x, y values to xValueMapper, yValueMapper properties respectively.

SfCircularChart(
  series: <CircularSeries<SampleData, String>>[
    PieSeries<SampleData, String>(
      dataSource: chartData,
      xValueMapper: (SampleData data, _) => data.x,
      yValueMapper: (SampleData data, _) => data.y)
    ],
  )

Step 3: Declare the onPointTap event in the SfCircularChart, assign the tapped segment index value from the event to the pointIndex variable. And set the radius value as per your requirement, then call setState method to make the changes reflected while tapping on the segment.

After that using the pointRadiusMapper set the radius value to the respective selected point with help of the pointIndex value. Here for the tapped segment we have assigned radius as 160 and 140 for the rest of the segments, you can change this based on your scenario.

SfCircularChart(
   series: <CircularSeries<SampleData, String>>[
       PieSeries<SampleData, String>(
          onPointTap: (ChartPointDetails details) {
              pointIndex = details.pointIndex;
              radius = '160';
              setState(() {});
          },
          pointRadiusMapper: (SampleData data, index) =>
                radius != '' && index == pointIndex ? radius : '140',
  ],
)

 Thus, the tapped segment size gets increased using the onPointTap callback and pointRadiusMapper properties.

View the sample in GitHub.

Conclusion

I hope you enjoyed learning about how to increase the size of the tapped segment in the pie chart.

You can refer to our  Flutter CartesianChart feature tour page to know about its other groundbreaking feature representations. You can also explore our Flutter CartesianChart documentation to understand how to create and manipulate data.

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