api - How to get data from coinapi when only press a button flutter

Question

I'm using this link from the coinapi web but it gives real time data I want a data when I press a button need solution or coinapi link I've read the coinapi complete documentation but I cant find any solution over there need a link or solution that gives me data when I clicked a button or when I require some data from coinapi.

code here:

class _MainPageState extends State<MainPage> {
      double dollars;
      String selectedValue = "USD";
      List<DropdownMenuItem> getDropDown() {
        List<DropdownMenuItem<String>> menuItems = [];
        for (String items in list) {
          var item = DropdownMenuItem(
            child: Text(items),
            value: items,
          );
          menuItems.add(item);
        }
        return menuItems;
      }
    
      @override
      void initState() {
        // TODO: implement initState
        super.initState();
        getNetData();
      }
    
      void getNetData() async {
        HTTP.Response response = await HTTP.get(
            'https://rest.coinapi.io/v1/exchangerate/BTC/USD?apikey=myKey';
        if (response.statusCode == 200) {
          setState(() {
            dollars = jsonDecode(response.body)['rate'];
          });
        } else
          print('Error');
      }
    
      @override
      Widget build(BuildContext context) {
        getNetData();
        getDropDown();
        return Column(
          mainAxisAlignment: MainAxisAlignment.spaceBetween,
          children: <Widget>[
            Row(
              mainAxisAlignment: MainAxisAlignment.center,
              children: <Widget>[
                Expanded(
                  child: Padding(
                    padding: EdgeInsets.all(20.0),
                    child: Container(
                      child: Card(
                        color: Colors.lightBlue,
                        child: ListTile(
                          title: Text(
                            '1 BTC = $dollars USD DOLLAR',
                            textAlign: TextAlign.center,
                          ),
                        ),
                      ),
                    ),
                  ),
                ),
              ],
            ),
            Row(
              children: <Widget>[
                Expanded(
                  child: Container(
                    height: 150.0,
                    color: Colors.lightBlue,
                    child: Center(
                      child: DropdownButton(
                        value: selectedValue,
                        items: getDropDown(),
                        onChanged: (value) {
                          setState(() {
                            selectedValue = value;
                          });
                        },
                      ),
                    ),
                  ),
                ),
              ],
            ),
          ],
        );
      }
    }

Answer 1

In your code in build and initState methods you retrieving the data from WEB but is not correct. If you need get the data each time when screen opening, you can use FutureBuilder widget (with it you can add a loader to providing information about current data retrieving state) and not call getNetData from initState. For update the data from a button (if you are choose FutureBuilder), just call setState (which calls build method again and reload value).

Something like this:

class _MainPageState extends State<MainPage> {
  String selectedValue = "USD";

  Future<String> getRate() async {
    HTTP.Response response = await HTTP.get('https://rest.coinapi.io/v1/exchangerate/BTC/$selectedValue?apikey=myKey');
    if (response.statusCode == 200) {
      return jsonDecode(response.body)['rate'];
    } else {
      // TODO: handle error code correctly
      return '';
    }
  }

  @override
  Widget build(BuildContext context) {
    return FutureBuilder<String>(
      future: getRate(),
      builder: (context, snapshot) {
        if (!snapshot.hasData) {
          // The data is loading, show progress
          return CircularProgressIndicator();
        }
        final rate = snapshot.data;
        return Column(
          mainAxisAlignment: MainAxisAlignment.spaceBetween,
          children: <Widget>[
            Row(
              mainAxisAlignment: MainAxisAlignment.center,
              children: <Widget>[
                Expanded(
                  child: Padding(
                    padding: EdgeInsets.all(20.0),
                    child: Container(
                      child: Card(
                        color: Colors.lightBlue,
                        child: ListTile(
                          title: Text(
                            '1 BTC = $rate USD DOLLAR',
                            textAlign: TextAlign.center,
                          ),
                        ),
                      ),
                    ),
                  ),
                ),
              ],
            ),
            Row(
              children: <Widget>[
                Expanded(
                  child: Container(
                    height: 150.0,
                    color: Colors.lightBlue,
                    child: Center(
                      child: DropdownButton(
                        value: selectedValue,
                        items: getDropDown(),
                        onChanged: (value) => setState(() {}),
                      ),
                    ),
                  ),
                ),
              ],
            ),
          ],
        );
      },
    );
  }

  List<DropdownMenuItem> getDropDown() {
    List<DropdownMenuItem<String>> menuItems = [];
    for (String items in list) {
      var item = DropdownMenuItem(
        child: Text(items),
        value: items,
      );
      menuItems.add(item);
    }
    return menuItems;
  }
}