在 flutter_bloc 包中处理对象后如何处理调度？

Question

I am using flutter_bloc & bloc package to manage state.

In child page i am initialize bloc & while back parent page dispose the bloc object.

When i comes back immediately on parent page that time bloc throw error Unhandled Exception: Bad state: Cannot add new events after calling close because on child page on load i am calling api in bloc. which trigger state after completed api. At that time already bloc object disposed.

[ERROR:flutter/lib/ui/ui_dart_state.cc(148)] Unhandled Exception: Bad state: Cannot add new events after calling close
E/flutter (17290): #0      _BroadcastStreamController.add (dart:async/broadcast_stream_controller.dart:249:24)
E/flutter (17290): #1      Subject._add (package:rxdart/src/subjects/subject.dart:124:16)
E/flutter (17290): #2      Subject.add (package:rxdart/src/subjects/subject.dart:118:5)
E/flutter (17290): #3      Bloc._bindStateSubject.<anonymous closure> (package:bloc/src/bloc.dart:90:23)
E/flutter (17290): #4      Stream.forEach.<anonymous closure>.<anonymous closure> (dart:async/stream.dart:814:45)
E/flutter (17290): #5      _runUserCode (dart:async/stream_pipe.dart:11:23)
E/flutter (17290): #6      Stream.forEach.<anonymous closure> (dart:async/stream.dart:814:11)
E/flutter (17290): #7      _rootRunUnary (dart:async/zone.dart:1132:38)
E/flutter (17290): #8      _CustomZone.runUnary (dart:async/zone.dart:1029:19)
E/flutter (17290): #9      _CustomZone.runUnaryGuarded (dart:async/zone.dart:931:7)
E/flutter (17290): #10     _BufferingStreamSubscription._sendData (dart:async/stream_impl.dart:336:11)
E/flutter (17290): #11     _BufferingStreamSubscription._add (dart:async/stream_impl.dart:263:7)
E/flutter (17290): #12     _SyncBroadcastStreamController._sendData (dart:async/broadcast_stream_controller.dart:375:20)
E/flutter (17290): #13     _BroadcastStreamController._add (dart:async/broadcast_stream_controller.dart:287:5)
E/flutter (17290): #14     _rootRunUnary (dart:async/zone.dart:1132:38)
E/flutter (17290): #15     _CustomZone.runUnary (dart:async/zone.dart:1029:19)
E/flutter (17290): #16     _CustomZone.runUnaryGuarded (dart:async/zone.dart:931:7)
E/flutter (17290): #17     _BufferingStreamSubscription._sendData (dart:async/stream_impl.dart:336:11)
E/flutter (17290): #18     _BufferingStreamSubscription._add (dart:async/stream_impl.dart:263:7)
E/flutter (17290): #19     _ForwardingStreamSubscription._add (dart:async/stream_pipe.dart:132:11)
E/flutter (17290): #20     _ForwardingStream._handleData (dart:async/stream_pipe.dart:98:10)
E/flutter (17290): #21     _ForwardingStreamSubscription._handleData (dart:async/stream_pipe.dart:164:13)
E/flutter (17290): #22     _rootRunUnary (dart:async/zone.dart:1132:38)
E/flutter (17290): #23     _CustomZone.runUnary (dart:async/zone.dart:1029:19)
E/flutter (17290): #24     _CustomZone.runUnaryGuarded (dart:async/zone.dart:931:7)
E/flutter (17290): #25     _BufferingStreamSubscription._sendData (dart:async/stream_impl.dart:336:11)
E/flutter (17290): #26     _DelayedData.perform (dart:async/stream_impl.dart:591:14)
E/flutter (17290): #27     _StreamImplEvents.handleNext (dart:async/stream_impl.dart:707:11)
E/flutter (17290): #28     _PendingEvents.schedule.<anonymous closure> (dart:async/stream_impl.dart:667:7)
E/flutter (17290): #29     _rootRun (dart:async/zone.dart:1120:38)
E/flutter (17290): #30     _CustomZone.run (dart:async/zone.dart:1021:19)
E/flutter (17290): #31     _CustomZone.runGuarded (dart:async/zone.dart:923:7)
E/flutter (17290): #32     _CustomZone.bindCallbackGuarded.<anonymous closure> (dart:async/zone.dart:963:23)
E/flutter (17290): #33     _rootRun (dart:async/zone.dart:1124:13)
E/flutter (17290): #34     _CustomZone.run (dart:async/zone.dart:1021:19)
E/flutter (17290): #35     _CustomZone.runGuarded (dart:async/zone.dart:923:7)
E/flutter (17290): #36     _CustomZone.bindCallbackGuarded.<anonymous closure> (dart:async/zone.dart:963:23)
E/flutter (17290): #37     _microtaskLoop (dart:async/schedule_microtask.dart:41:21)
E/flutter (17290): #38     _startMicrotaskLoop (dart:async/schedule_microtask.dart:50:5)

So how handle these when bloc already disposed ?

Answer 1

Use common bloc for parent and child. Create/Initialise bloc in parent when calling child do as following:

`BlocProvider.value( value: BlocProvider.of<BlocA>(context), child: ScreenA(), );`

By writing above you will keep alive the bloc from dispose, Then you can simply access bloc in child as following:

BlocProvider.of<BlocA>(context)

Just don't dispose it in child, And then, when you go back to parent from child your bloc won't get disposed and it will only dispose when parent destroy or dispose.

Everything is written there in readme: https://pub.dev/packages/flutter_bloc