Exception in converter function is not shown anywhere.

[sidlatau]

If exception is thrown in converter function it is not shown anywhere. Check an example app - exception is thrown when counter is odd number. App just works, but it shows only even numbers. It is difficult to catch such bugs. Exception is not visible anywhere - maybe at least it could be logged to console?

import 'package:flutter/material.dart';
import 'package:flutter_redux/flutter_redux.dart';
import 'package:redux/redux.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatelessWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  Widget build(BuildContext context) {
    return StoreProvider<AppState>(
      store: createStore(),
      child: StoreConnector<AppState, HomeViewModel>(
        distinct: true,
        converter: (store) => HomeViewModel.fromStore(store),
        builder: (_, viewModel) => Scaffold(
              appBar: AppBar(
                title: Text(title),
              ),
              body: Center(
                child: Column(
                  mainAxisAlignment: MainAxisAlignment.center,
                  children: <Widget>[
                    Text(
                      'You have pushed the button this many times:',
                    ),
                    Text(
                      '${viewModel.counter}',
                      style: Theme.of(context).textTheme.display1,
                    ),
                  ],
                ),
              ),
              floatingActionButton: FloatingActionButton(
                onPressed: viewModel.incrementCounter,
                tooltip: 'Increment',
                child: Icon(Icons.add),
              ),
            ),
      ),
    );
  }
}

class AppState {
  final int counter;

  AppState(this.counter);

  @override
  bool operator ==(Object other) =>
      identical(this, other) ||
      other is AppState &&
          runtimeType == other.runtimeType &&
          counter == other.counter;

  @override
  int get hashCode => counter.hashCode;
}

Store<AppState> createStore() {
  return Store(appReducer, initialState: AppState(0));
}

AppState appReducer(AppState state, dynamic action) {
  if (action is IncreaseCounterAction) {
    return AppState(state.counter + 1);
  }
  return state;
}

class IncreaseCounterAction {}

class HomeViewModel {
  factory HomeViewModel.fromStore(Store<AppState> store) {
    if (store.state.counter.isOdd) {
      throw Exception('Error!');
    }

    return HomeViewModel(
        counter: store.state.counter,
        incrementCounter: () {
          store.dispatch(IncreaseCounterAction());
        });
  }

  Function incrementCounter;

  int counter;

  HomeViewModel({@required this.incrementCounter, @required this.counter});

  @override
  bool operator ==(Object other) =>
      identical(this, other) ||
      other is HomeViewModel &&
          runtimeType == other.runtimeType &&
          counter == other.counter;

  @override
  int get hashCode => counter.hashCode;
}

[brianegan]

Hey there -- hrm, good call. I'll check out how I can expose these errors

[rostyslavroshak]

What if we start with adding assert to stream builder, something like these:

  @override
  Widget build(BuildContext context) {
    return StreamBuilder<ViewModel>(
        stream: stream,
        builder: (context, snapshot) {
          assert(snapshot.error == null, 'snapshot has error ${snapshot.error}'); //at least you will see red flutter error in debug builds.
          return widget.builder(
            context,
            snapshot.hasData ? snapshot.data : latestValue,
          );
        });
  }

[arteminthesky]

I just ran into a similar problem, only I used onWillChange. If there is any error inside the callback, it is impossible to see it, moreover, the new state will not apply to the builder.

[nashfive]

Hey there! I ran into the same issue today too, and I lost almost a day trying to figure this out. Any idea how we can avoid those error to be swallowed ?

[brianegan]

Hey all -- thanks for the feedback and apologies on being slow on this one. I think since I generally test converter functions I didn't run into this as much, but it's an important topic.

I've got a branch going to help alleviate these issues. Could you please check out the following PR and tell me if it would help?

#170

[brianegan]

Fixed