Implemented the upload status snackbar on the home screen, created the [DistinctStreamTransformer] and refactored how screens decide when to show a snackbar

lib/src/blocs/event_bloc.dart

@@ -4,18 +4,18 @@ import 'dart:io';
 import 'package:meta/meta.dart';
 import 'package:rxdart/rxdart.dart';
 
+import '../mixins/upload_status_mixin.dart';
 import '../models/event_model.dart';
 import '../models/task_model.dart';
 import '../models/user_model.dart';
 import '../resources/firestore_provider.dart';
 import '../resources/firebase_storage_provider.dart';
 import '../services/auth_service.dart';
-import '../services/upload_status_service.dart';
 import '../utils.dart'
     show kTaskListPriorityTransforemer, getImageThumbnailPath;
 
 /// A business logic component that manages the state for an event screen.
-class EventBloc {
+class EventBloc extends Object with UploadStatusMixin {
   /// The name of the event being shown.
   final String eventName;
 
@@ -28,9 +28,6 @@ class EventBloc {
   /// An instace of the auth service.
   final AuthService _auth = authService;
 
-  /// An instance of the upload status service.
-  final UploadStatusService _uploadStatus = uploadStatusService;
-
   /// A subject of list of task model.
   final _tasks = BehaviorSubject<List<TaskModel>>();
 
@@ -49,9 +46,6 @@ class EventBloc {
   /// A subject of a cache that contains the image files.
   final _images = BehaviorSubject<Map<String, Future<File>>>();
 
-  /// A subject of a flag that indicates if there is a snack bar showing.
-  final _snackBarStatus = BehaviorSubject<bool>(seedValue: false);
-
   /// The event being managed by this bloc.
   EventModel _event;
 
@@ -74,13 +68,6 @@ class EventBloc {
   /// An observable of a cache of the images files.
   Observable<Map<String, Future<File>>> get images => _images.stream;
 
-  /// An observable of a flag that indicates whether or not a snackBar is
-  /// currently showing.
-  ValueObservable<bool> get snackBarStatus => _snackBarStatus.stream;
-
-  /// An observable of the status of files being uploaded.
-  Observable<UploadStatus> get uploadStatus => _uploadStatus.status;
-
   // Sinks getters.
   /// Starts the fetching process for an image given its path.
   Function(String) get fetchImage => _imagesFetcher.sink.add;
@@ -88,12 +75,10 @@ class EventBloc {
   /// Starts the fetching process for an image thumbail given its path.
   Function(String) get fetchThumbnail => _imagesThumbnailsFetcher.sink.add;
 
-  /// Updates the snack bar status.
-  Function(bool) get updateSnackBarStatus => _snackBarStatus.sink.add;
-
   EventBloc({
     @required this.eventName,
   }) {
+    initializeSnackBarStatus();
     _ready = _initUserAndEvent();
     _imagesFetcher.transform(_imagesTransformer()).pipe(_images);
     _imagesThumbnailsFetcher
@@ -159,8 +144,7 @@ class EventBloc {
   }
 
   void dispose() async {
-    await _snackBarStatus.drain();
-    _snackBarStatus.close();
+    await disposeUploadStatusMixin();
     await _imagesThumbnailsFetcher.drain();
     _imagesThumbnailsFetcher.close();
     await _imagesFetcher.drain();

lib/src/blocs/home_bloc.dart

@@ -3,6 +3,7 @@ import 'dart:async';
 import 'package:rxdart/rxdart.dart';
 
 import '../utils.dart' show kTaskListPriorityTransforemer;
+import '../mixins/upload_status_mixin.dart';
 import '../models/task_model.dart';
 import '../resources/firestore_provider.dart';
 import '../services/auth_service.dart';
@@ -10,7 +11,7 @@ import '../services/auth_service.dart';
 export '../services/auth_service.dart' show FirebaseUser;
 
 /// A business logic component that manages the state of the home screen.
-class HomeBloc {
+class HomeBloc extends Object with UploadStatusMixin {
   /// An instance of the auth service.
   final AuthService _auth = authService;
 
@@ -47,6 +48,10 @@ class HomeBloc {
   /// An observable of the current logged in user.
   Observable<FirebaseUser> get userStream => _auth.userStream;
 
+  HomeBloc() {
+    initializeSnackBarStatus();
+  }
+
   // TODO: Include the priority in the filtering.
   /// Returns a stream transformer that filters the task with the text from
   /// the search box.
@@ -106,6 +111,7 @@ class HomeBloc {
   }
 
   void dispose() async {
+    await disposeUploadStatusMixin();
     await _searchBoxText.drain();
     _searchBoxText.close();
     await _tasks.drain();

lib/src/mixins/upload_status_mixin.dart

@@ -0,0 +1,40 @@
+import 'dart:async';
+
+import 'package:rxdart/rxdart.dart';
+
+import '../utils.dart';
+import '../services/upload_status_service.dart';
+
+mixin UploadStatusMixin {
+  /// An instance of the upload status service.
+  final UploadStatusService uploadStatusSer = uploadStatusService;
+
+  /// A subject of a flag that indicates if there is a snack bar showing.
+  final snackBarStatusSubject = BehaviorSubject<bool>(seedValue: false);
+
+  /// An observable of a flag that indicates whether or not a snackBar is
+  /// currently showing.
+  ValueObservable<bool> get snackBarStatus => snackBarStatusSubject.stream;
+
+  /// Updates the snack bar status.
+  Function(bool) get updateSnackBarStatus => snackBarStatusSubject.sink.add;
+
+  /// An observable of the status of files being uploaded.
+  Observable<UploadStatus> get uploadStatus => uploadStatusSer.status;
+
+  Future<void> disposeUploadStatusMixin() async {
+    await snackBarStatusSubject.drain();
+    snackBarStatusSubject.close();
+  }
+
+  void initializeSnackBarStatus() {
+    uploadStatusService.status
+        .transform(StreamTransformer<UploadStatus, bool>.fromHandlers(
+          handleData: (value, sink) {
+            sink.add(value.numberOfFiles != 0);
+          },
+        ))
+        .transform(DistinctStreamTransformer())
+        .pipe(snackBarStatusSubject);
+  }
+}

lib/src/screens/event_screen.dart

@@ -41,12 +41,25 @@ class _EventScreenState extends State<EventScreen>
   /// Needed for showing snackbars.
   BuildContext _scaffoldContext;
 
+  StreamSubscription _snackBarStatusSubscription;
+
   initState() {
     super.initState();
     bloc = EventBloc(eventName: widget.eventName);
     bloc.fetchTasks();
     bloc.fetchImagesPaths();
     _tabController = TabController(vsync: this, length: 2);
+    _snackBarStatusSubscription = bloc.snackBarStatus.listen((bool visible) {
+      if (visible) {
+        showUploadStatusSnackBar(
+          _scaffoldContext,
+          bloc.uploadStatus,
+          bloc.updateSnackBarStatus,
+        );
+      } else {
+        Scaffold.of(_scaffoldContext).hideCurrentSnackBar();
+      }
+    });
   }
 
   Widget build(BuildContext context) {
@@ -164,7 +177,8 @@ class _EventScreenState extends State<EventScreen>
   Widget buildAddPictureButton() {
     return GradientTouchableContainer(
       radius: 8,
-      onTap: onAddPicturePressed,
+      onTap: () =>
+          Navigator.of(context).pushNamed('newImage/${bloc.eventName}'),
       child: Icon(
         Icons.camera_alt,
         color: Colors.white,
@@ -190,19 +204,8 @@ class _EventScreenState extends State<EventScreen>
     );
   }
 
-  // TODO: use a block provider instead of passing callbacks
-  Future<void> onAddPicturePressed() async {
-    await Navigator.of(context).pushNamed('newImage/${bloc.eventName}');
-    if (bloc.snackBarStatus.value == false) {
-      showUploadStatusSnackBar(
-        _scaffoldContext,
-        bloc.uploadStatus,
-        bloc.updateSnackBarStatus,
-      );
-    }
-  }
-
   void dispose() {
+    _snackBarStatusSubscription.cancel();
     bloc.dispose();
     super.dispose();
   }

lib/src/screens/home_screen.dart

@@ -1,6 +1,9 @@
+import 'dart:async';
+
 import 'package:flutter/material.dart';
 import 'package:font_awesome_flutter/font_awesome_flutter.dart';
 
+import '../utils.dart' show showUploadStatusSnackBar;
 import '../models/task_model.dart';
 import '../blocs/home_bloc.dart';
 import '../widgets/home_app_bar.dart';
@@ -20,10 +23,28 @@ class _HomeScreenState extends State<HomeScreen> {
   /// An instance of the bloc for this screen.
   final HomeBloc bloc = HomeBloc();
 
+  /// The context of the scaffold being shown.
+  ///
+  /// Needed for showing snackbars.
+  BuildContext _scaffoldContext;
+
+  StreamSubscription _snackBarStatusSubscription;
+
   @override
   initState() {
     super.initState();
     bloc.fetchTasks();
+    _snackBarStatusSubscription = bloc.snackBarStatus.listen((bool visible) {
+      if (visible) {
+        showUploadStatusSnackBar(
+          _scaffoldContext,
+          bloc.uploadStatus,
+          bloc.updateSnackBarStatus,
+        );
+      } else {
+        Scaffold.of(_scaffoldContext).hideCurrentSnackBar();
+      }
+    });
   }
 
   Widget build(BuildContext context) {
@@ -48,38 +69,43 @@ class _HomeScreenState extends State<HomeScreen> {
           floatingActionButton: FloatingActionButton(
             child: Icon(FontAwesomeIcons.plus),
             backgroundColor: Color(0xFF707070),
-            onPressed: () => _showDialog(context),
+            onPressed: () => Navigator.of(context).push(NewItemDialogRoute()),
           ),
           floatingActionButtonLocation: FloatingActionButtonLocation.endFloat,
           appBar: HomeAppBar(
             avatarUrl: userAvatarUrl,
             subtitle: 'Hello $userDisplayName!',
           ),
-          body: StreamBuilder(
-            stream: bloc.userTasks,
-            builder:
-                (BuildContext context, AsyncSnapshot<List<TaskModel>> snap) {
-              if (!snap.hasData) {
-                return Center(
-                  child: LoadingIndicator(),
-                );
-              }
-              return Stack(
-                overflow: Overflow.visible,
-                children: <Widget>[
-                  _buildTasksList(snap.data),
-                  // This container is needed to make it seem like the search box is
-                  // part of the app bar.
-                  Container(
-                    height: _searchBoxHeight / 2,
-                    width: double.infinity,
-                    color: Theme.of(context).cardColor,
-                  ),
-                  SearchBox(
-                    onChanged: bloc.updateSearchBoxText,
-                    height: 50.0,
-                  ),
-                ],
+          body: Builder(
+            builder: (BuildContext context) {
+              _scaffoldContext = context;
+              return StreamBuilder(
+                stream: bloc.userTasks,
+                builder: (BuildContext context,
+                    AsyncSnapshot<List<TaskModel>> snap) {
+                  if (!snap.hasData) {
+                    return Center(
+                      child: LoadingIndicator(),
+                    );
+                  }
+                  return Stack(
+                    overflow: Overflow.visible,
+                    children: <Widget>[
+                      _buildTasksList(snap.data),
+                      // This container is needed to make it seem like the search box is
+                      // part of the app bar.
+                      Container(
+                        height: _searchBoxHeight / 2,
+                        width: double.infinity,
+                        color: Theme.of(context).cardColor,
+                      ),
+                      SearchBox(
+                        onChanged: bloc.updateSearchBoxText,
+                        height: 50.0,
+                      ),
+                    ],
+                  );
+                },
               );
             },
           ),
@@ -88,10 +114,6 @@ class _HomeScreenState extends State<HomeScreen> {
     );
   }
 
-  void _showDialog(BuildContext context) {
-    Navigator.of(context).push(NewItemDialogRoute());
-  }
-
   Widget _buildTasksList(List<TaskModel> tasks) {
     return ListView(
       padding: EdgeInsets.only(top: _searchBoxHeight + 15),
@@ -118,6 +140,7 @@ class _HomeScreenState extends State<HomeScreen> {
 
   @override
   void dispose() {
+    _snackBarStatusSubscription.cancel();
     bloc.dispose();
     super.dispose();
   }

lib/src/utils.dart

@@ -1,4 +1,5 @@
 import 'dart:async';
+import 'dart:collection';
 
 import 'package:flutter/material.dart';
 import 'package:rxdart/rxdart.dart';
@@ -97,14 +98,12 @@ void showUploadStatusSnackBar(
         }
         print('Number of files: ${snap.data.numberOfFiles}');
         if (snap.data.numberOfFiles == 0) {
-          onSuccessfullyClosed(false);
-          scaffoldState.hideCurrentSnackBar();
-          return Text('');
+          return Text('Done!');
         }
         return Row(
           children: <Widget>[
             Spacer(),
-            Text('${snap.data.numberOfFiles} pending files'),
+            Text('${snap.data.numberOfFiles} pending'),
             Spacer(flex: 5),
             Text(snap.data.percentage + '%'),
             Spacer(),
@@ -114,3 +113,49 @@ void showUploadStatusSnackBar(
     ),
   ));
 }
+
+/// A transformer that only emits a value if it is different than the last one
+/// emitted.
+///
+/// The [==] operator is to check for inequality, be sure that the objects
+/// passing through the stream behave correctly with theses operator.
+class DistinctStreamTransformer<T> extends StreamTransformerBase<T, T> {
+  final StreamTransformer<T, T> transformer;
+
+  DistinctStreamTransformer() : transformer = _buildTransformer();
+
+  @override
+  Stream<T> bind(Stream<T> stream) => transformer.bind(stream);
+
+  static StreamTransformer<T, T> _buildTransformer<T>() {
+    return StreamTransformer<T, T>((Stream<T> input, bool cancelOnError) {
+      T last;
+      StreamController<T> controller;
+      StreamSubscription<T> subscription;
+
+      controller = StreamController<T>(
+          sync: true,
+          onListen: () {
+            subscription = input.listen(
+              (T value) {
+                if (!(last == value)) {
+                  last = value;
+                  controller.add(value);
+                }
+              },
+              onError: controller.addError,
+              onDone: controller.close,
+              cancelOnError: cancelOnError,
+            );
+          },
+          onPause: ([Future<dynamic> resumeSignal]) =>
+              subscription.pause(resumeSignal),
+          onResume: () => subscription.resume(),
+          onCancel: () {
+            return subscription.cancel();
+          });
+
+      return controller.stream.listen(null);
+    });
+  }
+}

lib/src/widgets/new_item_dialog_route.dart

@@ -1,3 +1,5 @@
+import 'dart:async';
+
 import 'package:flutter/material.dart';
 import 'package:flutter/cupertino.dart';