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Date: 2021-10-05 22:30:28 Functions: 0 0 -

          Line data    Source code
       1             : import 'dart:async';
       2             : 
       3             : import 'package:flutter/widgets.dart';
       4             : import 'package:flutter_bloc/flutter_bloc.dart';
       5             : import 'package:provider/single_child_widget.dart';
       6             : 
       7             : /// Mixin which allows `MultiBlocListener` to infer the types
       8             : /// of multiple [BlocListener]s.
       9             : mixin BlocListenerSingleChildWidget on SingleChildWidget {}
      10             : 
      11             : /// Signature for the `listener` function which takes the `BuildContext` along
      12             : /// with the `state` and is responsible for executing in response to
      13             : /// `state` changes.
      14             : typedef BlocWidgetListener<S> = void Function(BuildContext context, S state);
      15             : 
      16             : /// Signature for the `listenWhen` function which takes the previous `state`
      17             : /// and the current `state` and is responsible for returning a [bool] which
      18             : /// determines whether or not to call [BlocWidgetListener] of [BlocListener]
      19             : /// with the current `state`.
      20             : typedef BlocListenerCondition<S> = bool Function(S previous, S current);
      21             : 
      22             : /// {@template bloc_listener}
      23             : /// Takes a [BlocWidgetListener] and an optional [bloc] and invokes
      24             : /// the [listener] in response to `state` changes in the [bloc].
      25             : /// It should be used for functionality that needs to occur only in response to
      26             : /// a `state` change such as navigation, showing a `SnackBar`, showing
      27             : /// a `Dialog`, etc...
      28             : /// The [listener] is guaranteed to only be called once for each `state` change
      29             : /// unlike the `builder` in `BlocBuilder`.
      30             : ///
      31             : /// If the [bloc] parameter is omitted, [BlocListener] will automatically
      32             : /// perform a lookup using [BlocProvider] and the current `BuildContext`.
      33             : ///
      34             : /// ```dart
      35             : /// BlocListener<BlocA, BlocAState>(
      36             : ///   listener: (context, state) {
      37             : ///     // do stuff here based on BlocA's state
      38             : ///   },
      39             : ///   child: Container(),
      40             : /// )
      41             : /// ```
      42             : /// Only specify the [bloc] if you wish to provide a [bloc] that is otherwise
      43             : /// not accessible via [BlocProvider] and the current `BuildContext`.
      44             : ///
      45             : /// ```dart
      46             : /// BlocListener<BlocA, BlocAState>(
      47             : ///   value: blocA,
      48             : ///   listener: (context, state) {
      49             : ///     // do stuff here based on BlocA's state
      50             : ///   },
      51             : ///   child: Container(),
      52             : /// )
      53             : /// ```
      54             : /// {@endtemplate}
      55             : ///
      56             : /// {@template bloc_listener_listen_when}
      57             : /// An optional [listenWhen] can be implemented for more granular control
      58             : /// over when [listener] is called.
      59             : /// [listenWhen] will be invoked on each [bloc] `state` change.
      60             : /// [listenWhen] takes the previous `state` and current `state` and must
      61             : /// return a [bool] which determines whether or not the [listener] function
      62             : /// will be invoked.
      63             : /// The previous `state` will be initialized to the `state` of the [bloc]
      64             : /// when the [BlocListener] is initialized.
      65             : /// [listenWhen] is optional and if omitted, it will default to `true`.
      66             : ///
      67             : /// ```dart
      68             : /// BlocListener<BlocA, BlocAState>(
      69             : ///   listenWhen: (previous, current) {
      70             : ///     // return true/false to determine whether or not
      71             : ///     // to invoke listener with state
      72             : ///   },
      73             : ///   listener: (context, state) {
      74             : ///     // do stuff here based on BlocA's state
      75             : ///   }
      76             : ///   child: Container(),
      77             : /// )
      78             : /// ```
      79             : /// {@endtemplate}
      80             : class BlocListener<B extends BlocBase<S>, S> extends BlocListenerBase<B, S>
      81             :     with BlocListenerSingleChildWidget {
      82             :   /// {@macro bloc_listener}
      83             :   /// {@macro bloc_listener_listen_when}
      84           7 :   const BlocListener({
      85             :     Key? key,
      86             :     required BlocWidgetListener<S> listener,
      87             :     B? bloc,
      88             :     BlocListenerCondition<S>? listenWhen,
      89             :     Widget? child,
      90           7 :   }) : super(
      91             :           key: key,
      92             :           child: child,
      93             :           listener: listener,
      94             :           bloc: bloc,
      95             :           listenWhen: listenWhen,
      96             :         );
      97             : }
      98             : 
      99             : /// {@template bloc_listener_base}
     100             : /// Base class for widgets that listen to state changes in a specified [bloc].
     101             : ///
     102             : /// A [BlocListenerBase] is stateful and maintains the state subscription.
     103             : /// The type of the state and what happens with each state change
     104             : /// is defined by sub-classes.
     105             : /// {@endtemplate}
     106             : abstract class BlocListenerBase<B extends BlocBase<S>, S>
     107             :     extends SingleChildStatefulWidget {
     108             :   /// {@macro bloc_listener_base}
     109           7 :   const BlocListenerBase({
     110             :     Key? key,
     111             :     required this.listener,
     112             :     this.bloc,
     113             :     this.child,
     114             :     this.listenWhen,
     115           7 :   }) : super(key: key, child: child);
     116             : 
     117             :   /// The widget which will be rendered as a descendant of the
     118             :   /// [BlocListenerBase].
     119             :   final Widget? child;
     120             : 
     121             :   /// The [bloc] whose `state` will be listened to.
     122             :   /// Whenever the [bloc]'s `state` changes, [listener] will be invoked.
     123             :   final B? bloc;
     124             : 
     125             :   /// The [BlocWidgetListener] which will be called on every `state` change.
     126             :   /// This [listener] should be used for any code which needs to execute
     127             :   /// in response to a `state` change.
     128             :   final BlocWidgetListener<S> listener;
     129             : 
     130             :   /// {@macro bloc_listener_listen_when}
     131             :   final BlocListenerCondition<S>? listenWhen;
     132             : 
     133           7 :   @override
     134             :   SingleChildState<BlocListenerBase<B, S>> createState() =>
     135           7 :       _BlocListenerBaseState<B, S>();
     136             : }
     137             : 
     138             : class _BlocListenerBaseState<B extends BlocBase<S>, S>
     139             :     extends SingleChildState<BlocListenerBase<B, S>> {
     140             :   StreamSubscription<S>? _subscription;
     141             :   late B _bloc;
     142             :   late S _previousState;
     143             : 
     144           7 :   @override
     145             :   void initState() {
     146           7 :     super.initState();
     147          23 :     _bloc = widget.bloc ?? context.read<B>();
     148          21 :     _previousState = _bloc.state;
     149           7 :     _subscribe();
     150             :   }
     151             : 
     152           5 :   @override
     153             :   void didUpdateWidget(BlocListenerBase<B, S> oldWidget) {
     154           5 :     super.didUpdateWidget(oldWidget);
     155           7 :     final oldBloc = oldWidget.bloc ?? context.read<B>();
     156          10 :     final currentBloc = widget.bloc ?? oldBloc;
     157           5 :     if (oldBloc != currentBloc) {
     158           4 :       if (_subscription != null) {
     159           4 :         _unsubscribe();
     160           4 :         _bloc = currentBloc;
     161          12 :         _previousState = _bloc.state;
     162             :       }
     163           4 :       _subscribe();
     164             :     }
     165             :   }
     166             : 
     167           7 :   @override
     168             :   void didChangeDependencies() {
     169           7 :     super.didChangeDependencies();
     170          16 :     final bloc = widget.bloc ?? context.read<B>();
     171          14 :     if (_bloc != bloc) {
     172           1 :       if (_subscription != null) {
     173           1 :         _unsubscribe();
     174           1 :         _bloc = bloc;
     175           3 :         _previousState = _bloc.state;
     176             :       }
     177           1 :       _subscribe();
     178             :     }
     179             :   }
     180             : 
     181           7 :   @override
     182             :   Widget buildWithChild(BuildContext context, Widget? child) {
     183          15 :     if (widget.bloc == null) context.select<B, int>(identityHashCode);
     184             :     return child!;
     185             :   }
     186             : 
     187           7 :   @override
     188             :   void dispose() {
     189           7 :     _unsubscribe();
     190           7 :     super.dispose();
     191             :   }
     192             : 
     193           7 :   void _subscribe() {
     194          34 :     _subscription = _bloc.stream.listen((state) {
     195          15 :       if (widget.listenWhen?.call(_previousState, state) ?? true) {
     196          18 :         widget.listener(context, state);
     197             :       }
     198           6 :       _previousState = state;
     199             :     });
     200             :   }
     201             : 
     202           7 :   void _unsubscribe() {
     203          14 :     _subscription?.cancel();
     204           7 :     _subscription = null;
     205             :   }
     206             : }

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