Refreshing Future Builder

[K Wilde]

Hi,

I'm trying to retrieve some data from a web endpoint periodically using future builder.  I can get it to work initially but subsequent calls do not cause the widget to update any idea how I can go about it?  Code is attached.  Thanks in advance

import 'package:flutter/material.dart';
import 'dart:async';
import 'dart:convert';
import 'package:http/http.dart' as http;
//import 'comms.dart' as comms;
import 'types.dart' as userTypes;
import 'data_item.dart';
import 'data_item_detail.dart';
import 'globals.dart' as Globals;


class Post{
  final int userId;
  final int id;
  final String title;
  final List tagList;

  Post({this.userId,this.id,this.title,this.tagList});

  factory Post.fromJson(Map<String,dynamic> json){
    return Post(
      userId: json["userId"],
      id: json["id"],
      title: json["title"],
      tagList: json["tagList"],
    );
  }
}

Future<Post> fetchPost() async{
  String url = Uri.encodeFull(Globals.mainURL);
  var response = await http.get(url,headers:{"Accept":"application.json"});

  //print(response.body.toString());
  //print (response.statusCode.toString());

  if (response.statusCode == 200){
    // response is OK
    //print(Post.fromJson(json.decode(response.body)).body.toString());
    return Post.fromJson(json.decode(response.body));
  }else{
    throw Exception("Failed to load post");
  }
}


void main() {
  //await getDataInitial();
  runApp(new MyApp());
}

class MyApp extends StatelessWidget{

  @override
  Widget build(BuildContext context){

    return new MaterialApp(
      title: 'Mobile Data',
      theme: new ThemeData(
        primarySwatch: Colors.blue
      ),
      home: new MainPage(title:"Main Window"),
      routes: <String,WidgetBuilder>{
        '/data_item_detail':(BuildContext context) => new DataItemDetail(),
      }
    );
  }
}

class MainPage extends StatefulWidget{
  final String title;


  MainPage({Key key, this.title}) : super(key: key);

  @override
  _MainPageState createState() => new _MainPageState();

}

class _MainPageState extends State<MainPage> {

  _doUpdate(Timer t){

    fetchPost();
  }


  @override
  Widget build(BuildContext context) {

    new Timer.periodic(new Duration(seconds:10), _doUpdate);

    return new Scaffold(
        appBar: new AppBar(
          title: new Text(widget.title),
          backgroundColor: Colors.blue,
        ),
        body: Center(
          child: FutureBuilder<Post>(
            future: fetchPost(),
            
            builder: (context, snapshot) {
              //print(snapshot.data.title);
              //print (snapshot.connectionState.toString());
              if (snapshot.hasData) {
                //return Text('${snapshot.data}');
                print("tagList " + snapshot.data.tagList.toString());
                return Text(snapshot.data.tagList[0]["value"].toStringAsFixed(2));
              } else if (snapshot.hasError) {
                return Text("${snapshot.error}");
              }
              return CircularProgressIndicator();
            },
          ),
        )
    );
  }
}

[Ralph Bergmann]

I think the best way to do that is to use a StreamBuilder in combination
with a BLoC. Your update method can fill the BLoC which will
automatically update the StreamBuilder.

I'm not sure, but I guess a FutureBuilder is for one update only and not
for continually updates.

You can see more about BLoC in this video:
https://www.youtube.com/watch?v=RS36gBEp8OI


Ralph



Am 25.07.18 um 03:38 schrieb K Wilde:

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[K Wilde]

Thanks for the reply.  I think you're right about the FutureBuilder  although I can't find where that is explicitly documented anywhere.  The reference video is quite good.  I'll have a go at Streams and BLoc.

[Ralph Bergmann]

Am 25.07.18 um 14:19 schrieb K Wilde:

> Thanks for the reply.  I think you're right about the FutureBuilder 
> although I can't find where that is explicitly documented anywhere.  The

It's between the lines ;-)


A Future can be completed in two ways: with a value ("the future
succeeds") or with an error ("the future fails"). Users can install
callbacks for each case.
https://docs.flutter.io/flutter/dart-async/Future-class.html


Widget rebuilding is scheduled by the completion of the future, using
State.setState, but is otherwise decoupled from the timing of the future.
https://docs.flutter.io/flutter/widgets/FutureBuilder-class.html


In other words: The Future completes with the first value and the
FutureBuilder uses this completion signal to build its ui.


Ralph

[Rudi Floren]

You can call setState to inform the stateful widget to redraw. And save the futures to a local variable in the State which you update during the update function.

Like

Future<> item = fetchPost()

And then use this local variable for the future attribute of the widget.

When you use

_doUpdate(Timer t){
setState({
item = fetchPost();
});
}

 

your widget should update.

Sry for the layout. Using my mobile right now.

Rudi

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[Mantas Liutkevičius]

This works, however, if you have a loader in your future builder it only works the first time, but does not appear on subsequent executions.