'方法'call'在null上被调用。'在颤振中

Question

我正在尝试从子小部件 PieChartWidget 中提取一个值 touchedIndex，我必须使用 fl_chart 在其父小部件 Co2Tracker 中制作一个中间有一个洞的饼图，以允许我在饼图的中间创建一些文本，当按下饼图的一部分时，这些文本会发生变化。这会返回一个错误，但除饼图段之外的所有内容都可以在视觉上运行。为了使调试更容易，我将setState(){isTouched = isTouchedNew} 替换为print(isTouchedNew)，但这仍然返回下面的错误，但是，饼图现在展开了。

PieChart example

使用回调函数时

int isTouched = -1;
setIsTouched(int isTouchedNew) {
  print(isTouchedNew);
}

集成在有状态的小部件中，我得到了输出

════════ Exception caught by gesture ═══════════════════════════════════════════════════════════════
The method 'call' was called on null.
Receiver: null
Tried calling: call(-1)

父主页

class Co2Tracker extends StatefulWidget {
  @override
  _Co2TrackerState createState() => _Co2TrackerState();
}

class _Co2TrackerState extends State<Co2Tracker> {

  List<String> pieNames = ['Travel', 'Gas', 'Electricity', 'Food shop', 'Water',];

  int isTouched = -1;
  double radiusNormal = 60;
  double centerRadius = 50;
  double radiusExpansion = 1.2;

  setIsTouched(int isTouchedNew) {
    print(isTouchedNew);
  }

  @override
  Widget build(BuildContext context) {

    //double co2 = ModalRoute.of(context).settings.arguments;

    return Scaffold(
      appBar: appBarTemplate('CO\u2082 Tracker'),
      body: Column(
        children: <Widget>[
          Padding(
            padding: const EdgeInsets.symmetric(vertical: 15),
            child: textStyleTemplateLarge(text: 'Your CO\u2082 emissions today', textColor: Colors.green[400]),
          ),
          AspectRatio(
            aspectRatio: 200/((radiusExpansion*radiusNormal) + centerRadius),
            child: Row(
              children: <Widget>[
                Expanded(
                  child: Stack(
                    children: <Widget>[
                      Center(
                        child: FlatButton(child: textStyleTemplateLarge(text: '70kg', textColor: Colors.black),),
                      ),
                      Center(
                          child: PieChartWidget(radiusNormal: radiusNormal, centerRadius: centerRadius, radiusExpanded: (radiusExpansion*radiusNormal), pieNames: pieNames,),
                      ),
                    ],
                  ),
                ),
              ],
            ),
          ),
        ],
      ),
    );
  }
}

子饼图小部件

import 'package:flutter/material.dart';
import 'package:fl_chart/fl_chart.dart';

class PieChartWidget extends StatefulWidget {
  final double radiusNormal;
  final double radiusExpanded;
  final double centerRadius;
  final double fontSizeNormal;
  final double fontSizeExpanded;
  final List<String> pieNames;
  final Function(int) setIsTouched;

  PieChartWidget({this.radiusNormal, this.radiusExpanded, this.centerRadius, this.fontSizeNormal, this.fontSizeExpanded, this.pieNames, this.setIsTouched});



  @override
  _PieChartWidgetState createState() => _PieChartWidgetState(radiusNormal: radiusNormal, radiusExpanded: radiusExpanded, centerRadius: centerRadius,
    fontSizeNormal: fontSizeNormal, fontSizeExpanded: fontSizeExpanded, pieNames: pieNames, setIsTouched: setIsTouched,);
}

class _PieChartWidgetState extends State<PieChartWidget> {
  int touchedIndex = -1;
  double radiusNormal;
  double radiusExpanded;
  double centerRadius;
  double fontSizeNormal;
  double fontSizeExpanded;
  List<String> pieNames;
  Function(int) setIsTouched;

  _PieChartWidgetState({this.radiusNormal = 50, this.radiusExpanded = 60, this.centerRadius = 40, this.fontSizeNormal = 16, this.fontSizeExpanded = 25,
    this.pieNames, this.setIsTouched,});

  @override
  Widget build(BuildContext context) {
    return PieChart(
      PieChartData(
        sections: pieSections(pieNames),
        borderData: FlBorderData(show: false),
        sectionsSpace: 0,
        centerSpaceRadius: centerRadius,
        pieTouchData: PieTouchData(touchCallback: (pieTouchResponse) {
          setState(() {
            if (pieTouchResponse.touchInput is FlLongPressEnd ||
                pieTouchResponse.touchInput is FlPanEnd) {
              touchedIndex = -1;
            } else {
              touchedIndex = pieTouchResponse.touchedSectionIndex;
            }
          });
          widget.setIsTouched(touchedIndex);
        }),
      ),
    );
  }

-----------------I-think-everything-below-this-is-irrelevant-but-I-could-be-wrong-------------------------------------------

  List<PieChartSectionData> pieSections(List<String> pieNames,) {
    return List.generate(5, (i) {
      final isTouched = i == touchedIndex;
      final double fontSize = isTouched ? 25 : 16;
      final double radius = isTouched ? radiusExpanded : radiusNormal;
      final int colorNumber = (1+i) * 100;
      final List<double> valueList = [20, 10, 10, 20, 30];
      final double total = valueList.fold(0, (a, b) => a+b);
      switch (i) {
        case 0:
          return sectionData(valueList[i], Colors.pink[300], title(isTouched, valueList[i], total, pieNames[i]), radius, fontSize);
        case 1:
          return sectionData(valueList[i], Colors.blue[600], title(isTouched, valueList[i], total, pieNames[i]), radius, fontSize);
        case 2:
          return sectionData(valueList[i], Colors.amber[300], title(isTouched, valueList[i], total, pieNames[i]), radius, fontSize);
        case 3:
          return sectionData(valueList[i], Colors.purple[300], title(isTouched, valueList[i], total, pieNames[i]), radius, fontSize);
        case 4:
          return sectionData(valueList[i], Colors.blue[300], title(isTouched, valueList[i], total, pieNames[i]), radius, fontSize);
        default:
          return null;
      }
    });
  }
  PieChartSectionData sectionData(double value, Color color, String title, double radius, double fontSize,){
    return PieChartSectionData(
      value: value, color: color, title: title, radius: radius,
      titleStyle: TextStyle(color: Colors.black, fontSize: fontSize, fontWeight: FontWeight.bold),
    );
  }
  String title(bool isTouched, double value, double total, String title,) {
    return isTouched ? '${double.parse((value/total*100).toStringAsFixed(2))}%' : '$title';
  }
}

到目前为止，我的想法可能与变量的初始化有关，或者可能与子页面第 43 行中的 touchCallback 函数有关，但到目前为止还没有运气。 提前感谢您的宝贵时间。

Answer 1

问题是当你打印一个整数时。

setIsTouched(int isTouchedNew) { print(isTouchedNew); }

你应该像这样打印它

print("${isTouchedNew}")

Answer 2

嗯..不确定您是否尝试过，

int isTouched = -1;


setIsTouched(int isTouchedNew) {
setState(() {

isTouched=isTouchedNew;
  print(isTouchedNew);
}
}