Rxdart combinelaststream function does not work - flutter

Question

I am going to combine two stream. But it does not work. What is my mistake ?
My build function is ;
#override
Widget build(BuildContext context) {
return StreamBuilder(
stream: Observable.combineLatest2(
getAllDBAccountsBloc.getAllDBAccountsStream,
deleteDBAccountBloc.deleteDBAccountStream,
(accountList, deleteAccountResultModel) {
print("my account list : ${accountList == null}");
return AccountsCombinerResult(
deleteAccountResultBlocModel: deleteAccountResultModel,
accountsList: accountList,
);
},
),
builder: (context, snapshot) {
print("hasData : ${snapshot.hasData}");
if (snapshot.hasData) accountsCombinerResult = snapshot.data;
if (snapshot.hasError) return Text(snapshot.error.toString());
return _buildWidget;
},
);
}
Get All DB Accounts Stream Bloc is
class GetAllDBAccountsBloc {
final _getAllDBAccountsFetcher = PublishSubject<List<AccountDatabaseModel>>();
Observable<List<AccountDatabaseModel>> get getAllDBAccountsStream => _getAllDBAccountsFetcher.stream;
getAllDBAccounts() async {
print("accounts getting");
_getAllDBAccountsFetcher.sink.add(null);
await new Future.delayed(const Duration(seconds: 1));
_getAllDBAccountsFetcher.sink.add(await Repository.getAllDBAccounts());
print("accounts get");
}
dispose() {
_getAllDBAccountsFetcher.close();
}
}
final getAllDBAccountsBloc = GetAllDBAccountsBloc();
Delete DB Account Bloc is
class DeleteDBAccountBloc {
final _deleteDBAccountFetcher = PublishSubject<DeleteAccountResultBlocModel>();
Observable<DeleteAccountResultBlocModel> get deleteDBAccountStream => _deleteDBAccountFetcher.stream;
deleteDBAccount(DeleteAccountRequestBlocModel requestModel) async {
_deleteDBAccountFetcher.sink.add(DeleteAccountResultBlocModel());
await new Future.delayed(const Duration(seconds: 1));
_deleteDBAccountFetcher.sink.add(await Repository.deleteDBAccount(requestModel));
}
dispose() {
_deleteDBAccountFetcher.close();
}
}
final deleteDBAccountBloc = DeleteDBAccountBloc();
Combiner result class is
class AccountsCombinerResult {
final DeleteAccountResultBlocModel deleteAccountResultBlocModel;
final List<AccountDatabaseModel> accountsList;
AccountsCombinerResult({
#required this.accountsList,
#required this.deleteAccountResultBlocModel,
});
}
its mine Run log on android studio..
I/flutter (28323): accounts getting
I/flutter (28323): hasData : false
I/flutter (28323): hasData : false
I/flutter (28323): accounts get
The stream work but i did not get AccountsCombiner Result data.
This build method work but i don't want use it...
#override
Widget build(BuildContext context) {
return StreamBuilder(
stream: getAllDBAccountsBloc.getAllDBAccountsStream,
builder: (context, getDbAccountsSnapshot) {
return StreamBuilder(
stream: deleteDBAccountBloc.deleteDBAccountStream,
builder: (context, deleteDbAccountStreamSnapshot) {
if (deleteDbAccountStreamSnapshot.hasData && getDbAccountsSnapshot.hasData) {
print("qweqweq");
accountsCombinerResult = AccountsCombinerResult(
accountsList: getDbAccountsSnapshot.data,
deleteAccountResultBlocModel: deleteDbAccountStreamSnapshot.data,
);
}
if (getDbAccountsSnapshot.hasError) return Text(getDbAccountsSnapshot.error.toString());
if (deleteDbAccountStreamSnapshot.hasError) return Text(deleteDbAccountStreamSnapshot.error.toString());
return _buildWidget;
},
);
},
);
}

Answer 1

You are building a new stream every time the build method is called. You need to keep the stream reference in the state.
StreamController<AccountsCombinerResult> _streamController = StreamController<AccountsCombinerResult>();
#override
void initState() {
super.initState();
_streamController.addStream(Observable.combineLatest2(
getAllDBAccountsBloc.getAllDBAccountsStream,
deleteDBAccountBloc.deleteDBAccountStream,
(accountList, deleteAccountResultModel) {
print("my account list : ${accountList == null}");
return AccountsCombinerResult(
deleteAccountResultBlocModel: deleteAccountResultModel,
accountsList: accountList,
);
},
));
}
#override
void dispose() {
super.dispose();
_streamController.close();
}
#override
Widget build(BuildContext context) {
return StreamBuilder(
stream: _streamController.stream,
builder: (context, snapshot) {
print("hasData : ${snapshot.hasData}");
if (snapshot.hasData) accountsCombinerResult = snapshot.data;
if (snapshot.hasError) return Text(snapshot.error.toString());
return _buildWidget;
},
);
}
To make this easier you could use the StreamProvider from the provider package.
https://pub.dev/packages/provider
https://pub.dev/documentation/provider/latest/provider/StreamProvider-class.html
It only build the stream once.
#override
Widget build(BuildContext context) {
return StreamProvider<AccountsCombinerResult>(
initialData: null, // not sure if this works, you can try []
create: () => Observable.combineLatest2(
getAllDBAccountsBloc.getAllDBAccountsStream,
deleteDBAccountBloc.deleteDBAccountStream,
(accountList, deleteAccountResultModel) {
print("my account list : ${accountList == null}");
return AccountsCombinerResult(
deleteAccountResultBlocModel: deleteAccountResultModel,
accountsList: accountList,
);
},
),
catchError: (context, error) => AccountsCombinerResult(
deleteAccountResultBlocModel: null,
accountsList: null,
error: error,
),
child: Builder(
builder: (context) {
final data = Provider.of<AccountsCombinerResult>(context);
// maybe null check
if (data.error != null) return Text(data.error.toString());
accountsCombinerResult =data;
return _buildWidget;
},
),
);
}
class AccountsCombinerResult {
final DeleteAccountResultBlocModel deleteAccountResultBlocModel;
final List<AccountDatabaseModel> accountsList;
final dynamic error;
AccountsCombinerResult({
#required this.accountsList,
#required this.deleteAccountResultBlocModel,
this.error,
});
}
The code is not tested so there may be typos or stuff that I missed, but you should get the general idea.