¿How can I iterate a snapshot in Flutter?

Question

I'm building a flutter app, and I'm trying to create a Time Chart based on a value obtained with a calculator, so I created a database with sqflite and each element in the db has an Id, a date, and a value.

import 'package:bezier_chart/bezier_chart.dart';
import 'package:flutter/material.dart';
import 'package:mi_working_app/components/bmi_chart.dart';
import 'package:mi_working_app/services/statistics_bmi_dbhelper.dart';

class StatisticsWidget extends StatefulWidget {
  @override
  _StatisticsWidgetState createState() => _StatisticsWidgetState();
}

class _StatisticsWidgetState extends State<StatisticsWidget> {
  BMIDbHelper bmihelper;

  @override
  void initState() {
    super.initState();
    bmihelper = BMIDbHelper();
  }

  @override
  Widget build(BuildContext context) {
    return Column(
      children: [
        FutureBuilder(
            future: bmihelper.getBMIs(),
            builder: (BuildContext context, AsyncSnapshot bmisnapshot) {
              if (bmisnapshot.hasData) {
                print(bmisnapshot.data);
                print(bmisnapshot.data.length);
                return Container(
                    child: BMITimeChart(
                  data: data(bmisnapshot),
                ));
              } else {
                return Center(
                  child: CircularProgressIndicator(),
                );
              }
            }),
      ],
    );
  }

}

Now to create the chart, I need to extract the date and value from each element, and for that I did this:

List<DataPoint<dynamic>> data(rawData) {
    List bmiDataList;

    for (Map m in rawData) {
      bmiDataList.add(DataPoint<DateTime>(
          value: double.parse(rawData.value['value']),
          xAxis: DateTime.parse(rawData.value['date'])));
    }

    print(bmiDataList);
    return bmiDataList;
  }

Now I'm getting the "type 'AsyncSnapshot<List>' is not a subtype of type 'Iterable'". I understand the error, I can't Iterate a snapshot, but I don't know how else can I retrieve the data

Solution

I believe passing,bmisnapshot.data should solve your error instead of passing bmisnapshot,

 return Container(
                    child: BMITimeChart(
                  data: data(bmisnapshot.data),
              ),);

Also always initialize your list if you are going use list methods, else you will get a NoSuchMethodError as it is called on null;

List bmiDataList = [];

And I'm unsure if this is right either,

    value: double.parse(rawData.value['value']),
          xAxis: DateTime.parse(rawData.value['date'])));

as AynscSnapshot has no value attribute, and since you're already passing in the data, you should be able to extract the values like this

    value: double.parse(rawData['value']),
          xAxis: DateTime.parse(rawData['date'])));

Comments

[Atul Chaudhary]

can you please share the error code with us for better understanding