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Cannot fetch data from api, Future always returns null - flutter

Asked 1 year ago
Viewed 826 times

I'm trying to fetch data from an API in a flutter. Just to test I was using the API URL: https://jsonplaceholder.typicode.com/todos/1 which has the following JSON object:

{
  "userId": 1,
  "id": 1,
  "title": "delectus aut autem",
  "completed": false
}

I followed an example online almost exactly just tweaked to match the workflow I want but the snapshot.hasData below returns false.

class Home extends StatelessWidget {
  final String accountNum;
  Home(this.accountNum);
  final String apiUrl = "https://jsonplaceholder.typicode.com/todos/";

  Future<Map<String, dynamic>> fetchData() async {
    //accountNum below is passed from a previous screen, in this case I pass '1'
    //I printed it to make sure that '1' is passed and it is correct
    var result = await http.get(apiUrl+accountNum);
    //I printed the below and it also gave me the json from the api
    //print(json.decode(result.body));
    return json.decode(result.body);
  }

  String _MeterNum(dynamic account){
    return account['title'];
  }

@override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Account Data'),
      ),
      body: Container(
        child: FutureBuilder<Map<String, dynamic>>(
          future: fetchData(),
          builder: (BuildContext context, AsyncSnapshot snapshot) {
            if(snapshot.hasData){
              print(_MeterNum(snapshot.data[0]));
              return ListView.builder(
                  padding: EdgeInsets.all(8),
                  itemCount: snapshot.data.length,
                  itemBuilder: (BuildContext context, int index){
                    return
                      Card(
                        child: Column(
                          children: <Widget>[
                            ListTile(
                              leading: CircleAvatar(
                                  radius: 30,
                                  backgroundImage: NetworkImage(snapshot.data[index]['picture']['large'])),
                              //I realize this will just show the same thing 
                              //but I was just keeping the format of the example I was following
                              title: Text(_MeterNum(snapshot.data[index])),
                              subtitle: Text(_MeterNum(snapshot.data[index])),
                              trailing: Text(_MeterNum(snapshot.data[index])),
                            )
                          ],
                        ),
                      );
                  });
            }else {
              return Center(child: CircularProgressIndicator());
            }
          },


        ),
      ),
    );
  }
}

What is returned is the CircularProgressIndicator() to the emulator screen indicating that snapshot.hasData is false. I don't get any error in the console or anything so I'm not sure how to proceed.

---EDIT--- Made changes to the code above using suggestions from the commenters:

Changed return type from Future<List> to Future<Map<String, dynamic>> and changed 'return json.decode(result.body)['results'];' to 'return json.decode(result.body)'

And now I get the following error:

The following NoSuchMethodError was thrown building FutureBuilder<Map<String, dynamic>>(dirty, state: _FutureBuilderState<Map<String, dynamic>>#a10d4):

The method '[]' was called on null. Receiver: null

Tried calling:[] ("title")

asked 1 year ago

Correct Answer

The API response is a JSON object

{
  "userId": 1,
  "id": 1,
  "title": "delectus aut autem",
  "completed": false
}

and contains only userId,id, title and completed memebers

instead of referring to an index please consider getting from the object.

replace

snapshot.data[index]

with

 snapshot.data

also

snapshot.data['picture']['large']

you don't have picture data in the JSON object, Try to comment that code or add a picture to it

answered 1 year ago

Other Answer

Before checking for hasData do this:

if (snapshot.connectionState == ConnectionState.done) {
              // your code
}

EDIT

Your request

var result = await http.get(apiUrl+accountNum);

returns JSON object not JSON List. But your fetchData method's return type was List before you updated it to Future<Map<String, dynamic>>. Write your method like this

Future<Map<String, dynamic>> fetchData() async {
    var result = await http.get(apiUrl+accountNum);
    return json.decode(result.body);
}

NO NEED FOR json.decode(result.body)['results'], because you are only fetching an object not a list.

answered 1 year ago