River_pod: ProviderListener missing events

[tbm98]

my code:

import 'package:flutter/material.dart';
import 'package:flutter_hooks/flutter_hooks.dart';
import 'package:hooks_riverpod/hooks_riverpod.dart';

import 'events/event_base.dart';
import 'events/loading_event.dart';
import 'events/show_snackbar_event.dart';

final eventProvider = StateProvider<EventBase>((ref) => null);

void main() {
  runApp(ProviderScope(child: 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,
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

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

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  void onChange(StateController<EventBase> event) {
    print(event.state);
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          title: Text(widget.title),
        ),
        body: ProviderListener(
          provider: eventProvider,
          onChange: onChange,
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[],
          ),
        ),
        floatingActionButton: FloatingActionButton(
          onPressed: () {
            context.read(eventProvider).state = LoadingEvent();
            context.read(eventProvider).state = ShowSnackbarEvent();
          },
          tooltip: 'Increment',
          child: Icon(Icons.add),
        ));
  }
}

Expected:

flutter: Instance of 'LoadingEvent'
flutter: Instance of 'ShowSnackbarEvent'

actually

flutter: Instance of 'ShowSnackbarEvent'

LoadingEvent is skiped.

[tbm98]

In the documentation.
Even if a provider changes many times in a quick succession, onChange will be called only once, at the end of the frame.
but I think it should triggers onChange if state is changed instead of call only once at the end of the frame

[rrousselGit]

What's the purpose?

[tbm98]

In a task, maybe something I want to pass more than one event to UI handle.
an example: loading dialog is showing and my http request done, then I want to dismisDialog and show snackbar for result success or fail.

[tbm98]

so still can pass successEvent to UI do both dismisDialog and showSnackbar but I think it will be more flexible if it is managed from providers.

[rrousselGit]

Maybe you shouldn't use StateProvider and instead use StateNotifierProvider with a custom StateNotifier

[tbm98]

What is that better than StateNotifier if I use StateNotifierProvider ?

[rrousselGit]

Actually, I'm not sure what you're trying to accomplish by writing:

context.read(eventProvider).state = LoadingEvent();
context.read(eventProvider).state = ShowSnackbarEvent();

StateNotifier is not an event queue, nor are providers.

Why not write showDialog/Navigator.pop directly inside the onPressed?

[tbm98]

Just for example. Actually I call it from providers.

So if I want to pass event like a queue to UI then what should i do ?

Vào 12:54, Th 5, 13 thg 8, 2020 Remi Rousselet [e-mail]
đã viết:

Actually, I'm not sure what you're trying to accomplish by writing:

context.read(eventProvider).state = LoadingEvent();
context.read(eventProvider).state = ShowSnackbarEvent();

StateNotifier is not an event queue, nor are providers.

Why not write showDialog/Navigator.pop directly inside the onPressed?

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[rrousselGit]

Maybe do context.read(eventProvider).addListener(...)

[tbm98]

I think addListener will be difficult to use in StatelessWidget or HookWidget because it should only be called once. So ProviderListener was born as a solution to the above problem and I think it should work like what addListener does as well.

[rrousselGit]

The thing is, Providers voluntarily do not call listeners immediately on change

This is for performance and maintainability reasons.

So you're better off with a custom WhateverListener for special objects

[tbm98]

Yes. maybe I need another way to solve it.
Thanks !