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Date: 2021-09-21 11:48:43 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/provider.dart';
       6             : import 'package:provider/single_child_widget.dart';
       7             : 
       8             : /// Mixin which allows `MultiBlocListener` to infer the types
       9             : /// of multiple [BlocListener]s.
      10             : mixin BlocListenerSingleChildWidget on SingleChildWidget {}
      11             : 
      12             : /// Signature for the `listener` function which takes the `BuildContext` along
      13             : /// with the `state` and is responsible for executing in response to
      14             : /// `state` changes.
      15             : typedef BlocWidgetListener<S> = void Function(BuildContext context, S state);
      16             : 
      17             : /// Signature for the `listenWhen` function which takes the previous `state`
      18             : /// and the current `state` and is responsible for returning a [bool] which
      19             : /// determines whether or not to call [BlocWidgetListener] of [BlocListener]
      20             : /// with the current `state`.
      21             : typedef BlocListenerCondition<S> = bool Function(S previous, S current);
      22             : 
      23             : /// {@template bloc_listener}
      24             : /// Takes a [BlocWidgetListener] and an optional [bloc] and invokes
      25             : /// the [listener] in response to `state` changes in the [bloc].
      26             : /// It should be used for functionality that needs to occur only in response to
      27             : /// a `state` change such as navigation, showing a `SnackBar`, showing
      28             : /// a `Dialog`, etc...
      29             : /// The [listener] is guaranteed to only be called once for each `state` change
      30             : /// unlike the `builder` in `BlocBuilder`.
      31             : ///
      32             : /// If the [bloc] parameter is omitted, [BlocListener] will automatically
      33             : /// perform a lookup using [BlocProvider] and the current `BuildContext`.
      34             : ///
      35             : /// ```dart
      36             : /// BlocListener<BlocA, BlocAState>(
      37             : ///   listener: (context, state) {
      38             : ///     // do stuff here based on BlocA's state
      39             : ///   },
      40             : ///   child: Container(),
      41             : /// )
      42             : /// ```
      43             : /// Only specify the [bloc] if you wish to provide a [bloc] that is otherwise
      44             : /// not accessible via [BlocProvider] and the current `BuildContext`.
      45             : ///
      46             : /// ```dart
      47             : /// BlocListener<BlocA, BlocAState>(
      48             : ///   value: blocA,
      49             : ///   listener: (context, state) {
      50             : ///     // do stuff here based on BlocA's state
      51             : ///   },
      52             : ///   child: Container(),
      53             : /// )
      54             : /// ```
      55             : /// {@endtemplate}
      56             : ///
      57             : /// {@template bloc_listener_listen_when}
      58             : /// An optional [listenWhen] can be implemented for more granular control
      59             : /// over when [listener] is called.
      60             : /// [listenWhen] will be invoked on each [bloc] `state` change.
      61             : /// [listenWhen] takes the previous `state` and current `state` and must
      62             : /// return a [bool] which determines whether or not the [listener] function
      63             : /// will be invoked.
      64             : /// The previous `state` will be initialized to the `state` of the [bloc]
      65             : /// when the [BlocListener] is initialized.
      66             : /// [listenWhen] is optional and if omitted, it will default to `true`.
      67             : ///
      68             : /// ```dart
      69             : /// BlocListener<BlocA, BlocAState>(
      70             : ///   listenWhen: (previous, current) {
      71             : ///     // return true/false to determine whether or not
      72             : ///     // to invoke listener with state
      73             : ///   },
      74             : ///   listener: (context, state) {
      75             : ///     // do stuff here based on BlocA's state
      76             : ///   }
      77             : ///   child: Container(),
      78             : /// )
      79             : /// ```
      80             : /// {@endtemplate}
      81             : class BlocListener<B extends BlocBase<S>, S> extends BlocListenerBase<B, S>
      82             :     with BlocListenerSingleChildWidget {
      83             :   /// {@macro bloc_listener}
      84             :   /// {@macro bloc_listener_listen_when}
      85           7 :   const BlocListener({
      86             :     Key? key,
      87             :     required BlocWidgetListener<S> listener,
      88             :     B? bloc,
      89             :     BlocListenerCondition<S>? listenWhen,
      90             :     Widget? child,
      91           7 :   }) : super(
      92             :           key: key,
      93             :           child: child,
      94             :           listener: listener,
      95             :           bloc: bloc,
      96             :           listenWhen: listenWhen,
      97             :         );
      98             : }
      99             : 
     100             : /// {@template bloc_listener_base}
     101             : /// Base class for widgets that listen to state changes in a specified [bloc].
     102             : ///
     103             : /// A [BlocListenerBase] is stateful and maintains the state subscription.
     104             : /// The type of the state and what happens with each state change
     105             : /// is defined by sub-classes.
     106             : /// {@endtemplate}
     107             : abstract class BlocListenerBase<B extends BlocBase<S>, S>
     108             :     extends SingleChildStatefulWidget {
     109             :   /// {@macro bloc_listener_base}
     110           7 :   const BlocListenerBase({
     111             :     Key? key,
     112             :     required this.listener,
     113             :     this.bloc,
     114             :     this.child,
     115             :     this.listenWhen,
     116           7 :   }) : super(key: key, child: child);
     117             : 
     118             :   /// The widget which will be rendered as a descendant of the
     119             :   /// [BlocListenerBase].
     120             :   final Widget? child;
     121             : 
     122             :   /// The [bloc] whose `state` will be listened to.
     123             :   /// Whenever the [bloc]'s `state` changes, [listener] will be invoked.
     124             :   final B? bloc;
     125             : 
     126             :   /// The [BlocWidgetListener] which will be called on every `state` change.
     127             :   /// This [listener] should be used for any code which needs to execute
     128             :   /// in response to a `state` change.
     129             :   final BlocWidgetListener<S> listener;
     130             : 
     131             :   /// {@macro bloc_listener_listen_when}
     132             :   final BlocListenerCondition<S>? listenWhen;
     133             : 
     134           7 :   @override
     135             :   SingleChildState<BlocListenerBase<B, S>> createState() =>
     136           7 :       _BlocListenerBaseState<B, S>();
     137             : }
     138             : 
     139             : class _BlocListenerBaseState<B extends BlocBase<S>, S>
     140             :     extends SingleChildState<BlocListenerBase<B, S>> {
     141             :   StreamSubscription<S>? _subscription;
     142             :   late B _bloc;
     143             :   late S _previousState;
     144             : 
     145           7 :   @override
     146             :   void initState() {
     147           7 :     super.initState();
     148          23 :     _bloc = widget.bloc ?? context.read<B>();
     149          21 :     _previousState = _bloc.state;
     150           7 :     _subscribe();
     151             :   }
     152             : 
     153           5 :   @override
     154             :   void didUpdateWidget(BlocListenerBase<B, S> oldWidget) {
     155           5 :     super.didUpdateWidget(oldWidget);
     156           7 :     final oldBloc = oldWidget.bloc ?? context.read<B>();
     157          10 :     final currentBloc = widget.bloc ?? oldBloc;
     158           5 :     if (oldBloc != currentBloc) {
     159           4 :       if (_subscription != null) {
     160           4 :         _unsubscribe();
     161           4 :         _bloc = currentBloc;
     162          12 :         _previousState = _bloc.state;
     163             :       }
     164           4 :       _subscribe();
     165             :     }
     166             :   }
     167             : 
     168           7 :   @override
     169             :   void didChangeDependencies() {
     170           7 :     super.didChangeDependencies();
     171          16 :     final bloc = widget.bloc ?? context.read<B>();
     172          14 :     if (_bloc != bloc) {
     173           1 :       if (_subscription != null) {
     174           1 :         _unsubscribe();
     175           1 :         _bloc = bloc;
     176           3 :         _previousState = _bloc.state;
     177             :       }
     178           1 :       _subscribe();
     179             :     }
     180             :   }
     181             : 
     182           7 :   @override
     183             :   Widget buildWithChild(BuildContext context, Widget? child) {
     184          15 :     if (widget.bloc == null) context.select<B, int>(identityHashCode);
     185             :     return child!;
     186             :   }
     187             : 
     188           7 :   @override
     189             :   void dispose() {
     190           7 :     _unsubscribe();
     191           7 :     super.dispose();
     192             :   }
     193             : 
     194           7 :   void _subscribe() {
     195          34 :     _subscription = _bloc.stream.listen((state) {
     196          15 :       if (widget.listenWhen?.call(_previousState, state) ?? true) {
     197          18 :         widget.listener(context, state);
     198             :       }
     199           6 :       _previousState = state;
     200             :     });
     201             :   }
     202             : 
     203           7 :   void _unsubscribe() {
     204          14 :     _subscription?.cancel();
     205           7 :     _subscription = null;
     206             :   }
     207             : }

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