Flutter - StreamBuilder - Refresh - flutter

Question

I have a StreamBuilder inside my Widget build of UserListDart:
StreamBuilder(
stream: stream.asStream(),
builder: (BuildContext context, AsyncSnapshot snapshot) {
if(snapshot.hasData) {
return Expanded(
child: ListView.builder(
itemCount: snapshot.data.length,
itemBuilder: (BuildContext context, int index) {
return ListTile(
title: Text(
snapshot.data[index].firstname + " " +
snapshot.data[index].lastname
),
onTap: () {
Navigator.of(context).push(DetailScreenDart(snapshot.data[index]));
},
);
}
)
);
}
}
...
)
The Stream is defined in the initState:
Future<List> stream;
#override
void initState() {
super.initState();
stream = fetchPost();
}
The fetchPost() is an api call:
Future<List<User>> fetchPost() async {
final response = await http.get('url');
final jsonResponse = json.decode(response.body);
List<User> users = [];
for(var u in jsonResponse){
User user = User(
firstname: u["firstname"],
lastname: u["lastname"],
);
users.add(user);
}
return users;
}
I Navigate to another Page to change for example the firstname (api get updated) and I Navigate back to the UserList:
Navigator.pushReplacement(
context,
new MaterialPageRoute(builder: (context) => new UserListDart())
).then((onValue) {
fetchPost();
});
But the StreamBuilder won't get updated and I don't know why.
Note:
I think the StreamBuilder don't realise that a change has happend when I navigate back. It only applies the changes if I reopen the Page..

Answer 1

You should be using setState and updating your stream variable with the result of the fetchList() call:
Navigator.pushReplacement(
context,
new MaterialPageRoute(builder: (context) => new UserListDart())
).then((onValue) {
setState((){
stream = fetchPost();
});
});
Here's a working example of what you want to achieve:
class StreamBuilderIssue extends StatefulWidget {
#override
_StreamBuilderIssueState createState() => _StreamBuilderIssueState();
}
class _StreamBuilderIssueState extends State<StreamBuilderIssue> {
Future<List<String>> futureList;
List<String> itemList = [
'item 1',
'item 1',
'item 1',
'item 1',
'item 1',
];
#override
void initState() {
futureList = fetchList();
super.initState();
}
#override
Widget build(BuildContext context) {
return Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
crossAxisAlignment: CrossAxisAlignment.center,
children: <Widget>[
Expanded(
child: Center(
child: StreamBuilder(
stream: futureList.asStream(),
builder: (context, snapshot){
if(snapshot.hasData){
return ListView.builder(
itemCount: snapshot.data.length,
itemBuilder: (context, index){
return Text(snapshot.data[index]);
},
);
}else{
return CircularProgressIndicator();
}
},
),
),
),
RaisedButton(
onPressed: goToAnotherView,
child: Text('Next View'),
),
RaisedButton(
onPressed: addItem,
child: Text('AddItem'),
)
],
),
);
}
Future<List<String>> fetchList(){
return Future.delayed(Duration(seconds: 2), (){
return itemList;
});
}
void goToAnotherView(){
Navigator.push(context, MaterialPageRoute(
builder: (context){
return StreamBuilderIssueNewView(addItem);
})
).then((res){
setState(() {
futureList = fetchList();
});
});
}
void addItem(){
itemList.add('anotherItem');
}
}
class StreamBuilderIssueNewView extends StatelessWidget {
final Function buttonAction;
StreamBuilderIssueNewView(this.buttonAction);
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(),
body: Center(
child: Column(
children: <Widget>[
Text('New view'),
RaisedButton(
onPressed: buttonAction,
child: Text('AddItem'),
)
],
),
),
);
}
}
By the way, you could also just use a FutureBuilder as your are not using a real Stream here, just an api fetch and you have to update with setState anyway.