Add optional condition to BlocListener

[GiancarloCode]

Status

Development

Breaking Changes

NO

Description

Add an optional condition property to BlocListener which takes the previousState and currentState as arguments and must return a bool which determines whether or not call listener

Usage

import 'package:equatable/equatable.dart';

enum SessionState { notInitialized, signedIn, notSignedIn }

class AuthState extends Equatable {
  final bool isLoading;
  final SessionState sessionState;

  AuthState(this.isLoading, this.sessionState)
      : super([isLoading, sessionState]);
}

...
@override
  Stream<AuthState> mapEventToState(AuthEvent event) async*{
    if (event == AuthEvent.SignOut) {
      yield currentState.copyWith(true);
      await _signOut();
      yield currentState.copyWith(false, SessionState.notSignedIn);
    }
  }
...

...
@override
  Widget build(BuildContext context) {
    return BlocListener(
      bloc: authBloc,
      condition: (AuthState previous, AuthState current) =>
          previous.sessionState != current.sessionState,
      listener: (BuildContext context, AuthState state) {
        if (state.sessionState == SessionState.signedIn) {
          Navigator.pushNamed(context, HomeScreen.routeName);
        }
      },
      child: MyChild(),
    );
  }
...

In the above example, the listener push a widget only when sessionState change to signedIn.

Without condition, this widget push multiple times HomeScreen when isLoading change and sessionState is signedIn , for example when try to sign out, the state change because isLoading change but while sessionState is signedIn, the listener push HomeScreen again.

This is only a example, you can imagine other cases with other bloc, when you need to show a dialog, snakcbar, etc.

Todos

• Tests
• Documentation
• Examples

Impact to Remaining Code Base

None

[codecov]

Codecov Report

Merging #406 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master   #406   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files          11     11           
  Lines         174    179    +5     
=====================================
+ Hits          174    179    +5

Impacted Files	Coverage Δ
packages/flutter_bloc/lib/src/bloc_listener.dart	100% <100%> (ø)	⬆️

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[felangel]

Thanks for the contribution! LGTM 👍