BlocBuilder with Optional Build Condition #315
Description
Is your feature request related to a problem? Please describe.
Proposal to address #174
Describe the solution you'd like
Proposing to add an optional condition property to BlocBuilder which takes the previousState and currentState as arguments and must return a bool which determines whether or not to rebuild.
Usage
@override
Widget build(BuildContext context) {
final TimerBloc _timerBloc = BlocProvider.of<TimerBloc>(context);
return Scaffold(
appBar: AppBar(title: Text('Flutter Timer')),
body: Column(
children: <Widget>[
BlocBuilder(
bloc: _timerBloc,
builder: (context, state) => TimerText(duration: state.duration),
),
BlocBuilder(
condition: (prevState, currState) =>
currState.runtimeType != prevState.runtimeType,
bloc: _timerBloc,
builder: (context, state) => Actions(),
),
],
),
);
}import 'package:equatable/equatable.dart';
import 'package:meta/meta.dart';
@immutable
abstract class TimerState extends Equatable {
final int duration;
TimerState(this.duration, [List props = const []])
: super([duration]..addAll(props));
}
class Ready extends TimerState {
Ready(int duration) : super(duration);
}
class Paused extends TimerState {
Paused(int duration) : super(duration);
}
class Running extends TimerState {
Running(int duration) : super(duration);
}
class Finished extends TimerState {
Finished() : super(0);
}In the above example, the Text widget with the remaining time will be rebuilt every time a new state is received (every second) whereas the Actions widget will only be rebuilt if the state runtimeType changes (Ready -> Running, Running -> Paused, etc...).
Describe alternatives you've considered
Lots of alternatives described in #174.