Question 76024 in Flutter Question posted in
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How do I get the variable from a Future function? – Flutter

I have a Future function that retrieves data. It performs well, however, my goal is to display the data in a widget. The problem is that I can’t seem to use the variable.

Here is the code I used for the Future function:

Future<void> param() async{
    String url1 = "my url";
    final response1 = await http.get(url1);
    String url2 = "my url";
    final response2 = await http.get(url2);
    String url3 = "my url";
    final response3 = await http.get(url3);
    String url4 = "my url";
    final response4 = await http.get(url4);

    field_1 fieldno1 = field_1.fromJson(jsonDecode(response1.body));
    field_2 fieldno2 = field_2.fromJson(jsonDecode(response2.body));
    field_3 fieldno3 = field_3.fromJson(jsonDecode(response3.body));
    field_4 fieldno4 = field_4.fromJson(jsonDecode(response4.body));

    final String? co2 = fieldno1.field1;
    final String? pm25 = fieldno2.field2;
    final String? temp = fieldno3.field3;
    final String? humi = fieldno4.field4;

    print(co2);
    print(pm25);
    print(temp);
    print(humi);
  }

And here is where I wish to put my variable (co2):

Container(
              height: 100,
              margin: const EdgeInsets.only(top: 20, bottom: 20, left: 15, right: 15,),
              padding: const EdgeInsets.only(right: 40, left: 30),
              decoration: BoxDecoration(
                color: co2 > 1000 ? Color(0xFFF1954A) : Color(0xFF7dbd0c),
                borderRadius: const BorderRadius.all(Radius.circular(15.0)),),
              child: sub(co2, "2" , "CO", "Carbon Dioxide","ppm"),
            ),
Tags:

2

Answers


  1. 0

    There are two mistakes

    1. You are not returning anything from the future<void> param() function
    2. You have to replace Container to FutureBuilder to access variable from future function

    Example:

    Future function:

    Future<String> getData() {
  return Future.delayed(Duration(seconds: 2), () {
    return "I am data";
    // throw Exception("Custom Error");
  });
}

    FutureBuilder:

    FutureBuilder(
  builder: (ctx, snapshot) {
    ... some code here
       
    // Displaying LoadingSpinner to indicate waiting state
    return Center(
      child: CircularProgressIndicator(),
    );
  },
   
  // Future that needs to be resolved
  // inorder to display something on the Canvas
  future: getData(),
),
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  2. 0

    You have multiple variables to return.

    in this case, you can do it like below:

    import 'package:flutter/material.dart';

class MyDataView extends StatefulWidget {
  @override
  _MyDataViewState createState() => _MyDataViewState();
}

class _MyDataViewState extends State<MyDataView> {
  Future<Map<String, dynamic>>? futureData;

  @override
  void initState() {
    super.initState();
    futureData = param();
  }

  Future<Map<String, dynamic>> param() async {
    String url1 = "my url";
    final response1 = await http.get(url1);
    String url2 = "my url";
    final response2 = await http.get(url2);
    String url3 = "my url";
    final response3 = await http.get(url3);
    String url4 = "my url";
    final response4 = await http.get(url4);

    field_1 fieldno1 = field_1.fromJson(jsonDecode(response1.body));
    field_2 fieldno2 = field_2.fromJson(jsonDecode(response2.body));
    field_3 fieldno3 = field_3.fromJson(jsonDecode(response3.body));
    field_4 fieldno4 = field_4.fromJson(jsonDecode(response4.body));

    final String? co2 = fieldno1.field1;
    final String? pm25 = fieldno2.field2;
    final String? temp = fieldno3.field3;
    final String? humi = fieldno4.field4;

    print(co2);
    print(pm25);
    print(temp);
    print(humi);

    Map<String, dynamic> data = {
      "co2": co2,
      "pm25": pm25,
      "temp": temp,
      "humi": humi,
    };

    return data;
  }

  @override
  Widget build(BuildContext context) {
    return FutureBuilder<Map<String, dynamic>>(
      future: futureData,
      builder: (context, snapshot) {
        if (snapshot.hasData) {
          return Container(
            padding: const EdgeInsets.all(16.0),
            child: Column(
              children: [
                Text("CO2: ${snapshot.data!['co2']}"),
                Text("PM25: ${snapshot.data!['pm25']}"),
                Text("Temperature: ${snapshot.data!['temp']}"),
                Text("Humidity: ${snapshot.data!['humi']}"),
              ],
            ),
          );
        } else if (snapshot.hasError) {
          return Text("${snapshot.error}");
        }
        return const CircularProgressIndicator();
      },
    );
  }
}
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