fix of #341

lib/blocs/app_bloc.dart

@@ -370,13 +370,13 @@ class StudyAppBLoC extends ChangeNotifier {
     Sensing().controller?.dispose();
   }
 
-  /// Add a [Measurement] object to the stream of measurements.
+  /// Add [measurement] to the stream of collected measurements.
   void addMeasurement(Measurement measurement) =>
-      Sensing().controller!.executor.addMeasurement(measurement);
+      Sensing().controller?.executor.addMeasurement(measurement);
 
-  /// Add a error to the stream of measurements.
+  /// Add [error] to the stream of measurements.
   void addError(Object error, [StackTrace? stacktrace]) =>
-      Sensing().controller!.executor.addError(error, stacktrace);
+      Sensing().controller?.executor.addError(error, stacktrace);
 
   /// Leave the study deployed on this phone.
   ///

lib/ui/pages/audio_task_page.dart

@@ -28,8 +28,10 @@ class AudioTaskPageState extends State<AudioTaskPage> {
       body: SafeArea(
         child: PopScope(
           canPop: true,
-          onPopInvoked: (didPop) async =>
-              _showCancelConfirmationDialog() as FutureOr<bool>,
+          // onPopInvokedWithResult: (didPop, result) =>
+          //     _showCancelConfirmationDialog(),
+          // onPopInvoked: (didPop) async =>
+          //     _showCancelConfirmationDialog() as FutureOr<bool>,
           child: Scaffold(
             body: Container(
               padding: const EdgeInsets.symmetric(horizontal: 15),
@@ -311,7 +313,7 @@ class AudioTaskPageState extends State<AudioTaskPage> {
                         radius: 30,
                         backgroundColor: CACHET.GREEN_1,
                         child: IconButton(
-                          onPressed: () => Navigator.pop(context),
+                          onPressed: () => Navigator.of(context).pop(),
                           padding: const EdgeInsets.all(0),
                           icon: const Icon(Icons.check_circle_outline,
                               color: Colors.white, size: 30),

lib/ui/pages/camera_task_page.dart

@@ -16,8 +16,8 @@ class CameraTaskPageState extends State<CameraTaskPage> {
   @override
   Widget build(BuildContext context) => PopScope(
         canPop: true,
-        onPopInvoked: (didPop) async =>
-            _showCancelConfirmationDialog() as FutureOr<bool>,
+        // onPopInvoked: (didPop) async =>
+        //     _showCancelConfirmationDialog() as FutureOr<bool>,
         child: Scaffold(
           body: Container(
               padding: const EdgeInsets.symmetric(horizontal: 15),

lib/ui/pages/login_page.dart

@@ -53,7 +53,7 @@ class _LoginPageState extends State<LoginPage> {
                   showDialog<bool>(
                     context: context,
                     builder: (context) => PopScope(
-                      onPopInvoked: (didPop) async {
+                      onPopInvokedWithResult: (didPop, result) async {
                         Navigator.of(context).pop();
                       },
                       child: EnableInternetConnectionDialog(),

lib/view_models/user_tasks.dart

@@ -28,11 +28,16 @@ class AppUserTaskFactory implements UserTaskFactory {
 }
 
 /// A user task handling audio recordings.
-/// When started, creates a [AudioTaskPage] and shows it to the user.
+///
+/// The [widget] returns an [AudioTaskPage] that can be shown on the UI.
+///
+/// When the recording is started (calling the [onRecordStart] method),
+/// the background task collecting sensor measures is started.
 class AudioUserTask extends UserTask {
   final StreamController<int> _countDownController =
       StreamController.broadcast();
   Stream<int>? get countDownEvents => _countDownController.stream;
+  Timer? _timer;
 
   /// Total duration of audio recording in seconds.
   int recordingDuration = 60;
@@ -46,7 +51,11 @@ class AudioUserTask extends UserTask {
         : 60;
   }
 
-  Timer? _timer;
+  @override
+  bool get hasWidget => true;
+
+  @override
+  Widget? get widget => AudioTaskPage(audioUserTask: this);
 
   /// Callback when recording is to start.
   void onRecordStart() {
@@ -80,17 +89,17 @@ class AudioUserTask extends UserTask {
 /// A user task handling video and image recordings.
 /// When started, creates a [CameraTaskPage].
 class VideoUserTask extends UserTask {
-  VideoUserTask(super.executor);
+  DateTime? _startRecordingTime, _endRecordingTime;
+  XFile? _file;
+  MediaType _mediaType = MediaType.image;
 
   @override
   bool get hasWidget => true;
 
   @override
   Widget? get widget => CameraTaskPage(mediaUserTask: this);
 
-  DateTime? _startRecordingTime, _endRecordingTime;
-  XFile? _file;
-  MediaType _mediaType = MediaType.image;
+  VideoUserTask(super.executor);
 
   /// Callback when a picture is captured.
   void onPictureCapture(XFile image) {

pubspec.lock

@@ -226,10 +226,10 @@ packages:
     dependency: "direct main"
     description:
       name: carp_audio_package
-      sha256: "49c6ce45287d4d922d52bad1c998e2239c637dc1fb3b1a335282acca106da8e8"
+      sha256: "3d6e3eccd58d4deabab5e1fc687e2d8205b92b489faeeecc33175d923895760e"
       url: "https://pub.dev"
     source: hosted
-    version: "1.7.0"
+    version: "1.7.1"
   carp_backend:
     dependency: "direct main"
     description:
@@ -282,10 +282,10 @@ packages:
     dependency: "direct main"
     description:
       name: carp_mobile_sensing
-      sha256: b7fcae43c84363f834f5f9143094720e4655c49614e438fa17d05d79c08a8a58
+      sha256: "58fdc4d7a4b9a6d2484fcc08153610971efe90992a03da874a77c8b33f164165"
       url: "https://pub.dev"
     source: hosted
-    version: "1.11.2"
+    version: "1.11.3"
   carp_movesense_package:
     dependency: "direct main"
     description:
@@ -1358,10 +1358,10 @@ packages:
     dependency: transitive
     description:
       name: path_parsing
-      sha256: e3e67b1629e6f7e8100b367d3db6ba6af4b1f0bb80f64db18ef1fbabd2fa9ccf
+      sha256: "45f7d6bba1128761de5540f39d5ca000ea8a1f22f06b76b61094a60a2997bd0e"
       url: "https://pub.dev"
     source: hosted
-    version: "1.0.1"
+    version: "1.0.2"
   path_provider:
     dependency: "direct main"
     description:
@@ -2091,11 +2091,10 @@ packages:
     dependency: transitive
     description:
       name: video_player_android
-      sha256: "641fc7221cfb3f25dd761d30cbe733046a3a4932fee09962adb80fd7d11fc663"
+      sha256: "391e092ba4abe2f93b3e625bd6b6a6ec7d7414279462c1c0ee42b5ab8d0a0898"
       url: "https://pub.dev"
     source: hosted
-    version: "2.7.15"
-
+    version: "2.7.16"
   video_player_avfoundation:
     dependency: transitive
     description:
@@ -2116,10 +2115,10 @@ packages:
     dependency: transitive
     description:
       name: video_player_web
-      sha256: "6dcdd298136523eaf7dfc31abaf0dfba9aa8a8dbc96670e87e9d42b6f2caf774"
+      sha256: "881b375a934d8ebf868c7fb1423b2bfaa393a0a265fa3f733079a86536064a10"
       url: "https://pub.dev"
     source: hosted
-    version: "2.3.2"
+    version: "2.3.3"
   vm_service:
     dependency: transitive
     description:
@@ -2180,10 +2179,10 @@ packages:
     dependency: transitive
     description:
       name: win32
-      sha256: e1d0cc62e65dc2561f5071fcbccecf58ff20c344f8f3dc7d4922df372a11df1f
+      sha256: "10169d3934549017f0ae278ccb07f828f9d6ea21573bab0fb77b0e1ef0fce454"
       url: "https://pub.dev"
     source: hosted
-    version: "5.7.1"
+    version: "5.7.2"
   win32_registry:
     dependency: transitive
     description: