Fixed Looking up a deactivated widget's ancestor

=> rrousselGit/provider#679 shows how to do if
you still want listeners

lib/start_plan_page.dart

@@ -29,7 +29,6 @@ class _StartPlanPageState extends State<StartPlanPage> {
   late List<String> planExercises;
 
   int selectedIndex = 0;
-  bool timerRunning = false;
   final repsNode = FocusNode();
   final weightNode = FocusNode();
 
@@ -40,28 +39,17 @@ class _StartPlanPageState extends State<StartPlanPage> {
     weightController = TextEditingController();
     planExercises = widget.plan.exercises.split(',');
     getLast();
-    Provider.of<AppState>(context, listen: false).addListener(updateRunning);
   }
 
   @override
   void dispose() {
-    Provider.of<AppState>(context, listen: false).removeListener(updateRunning);
     repsController.dispose();
     weightController.dispose();
     repsNode.dispose();
     weightNode.dispose();
     super.dispose();
   }
 
-  void updateRunning() {
-    final appState = Provider.of<AppState>(context, listen: false);
-    setState(() {
-      if (appState.secondsLeft == null)
-        timerRunning = false;
-      else
-        timerRunning = appState.secondsLeft! > 0;
-    });
-  }
 
   void selectWeight() {
     weightController.selection = TextSelection(
@@ -152,15 +140,19 @@ class _StartPlanPageState extends State<StartPlanPage> {
     if (!mounted) return;
     final appState = Provider.of<AppState>(context, listen: false);
     appState.updateSeconds(210000, 210000);
-    setState(() {
-      timerRunning = true;
-    });
+  }
+
+  bool isTimerRunning(BuildContext context) {
+    final secondsLeft = context.watch<AppState>().secondsLeft;
+    if (secondsLeft == null) return false;
+    return secondsLeft > 0;
   }
 
   @override
   Widget build(BuildContext context) {
     var title = widget.plan.days.replaceAll(",", ", ");
     title = title[0].toUpperCase() + title.substring(1).toLowerCase();
+    final timerRunning = isTimerRunning(context);
 
     return Scaffold(
       appBar: AppBar(
@@ -245,9 +237,6 @@ class _StartPlanPageState extends State<StartPlanPage> {
                 ? FloatingActionButton(
                     onPressed: () {
                       android.invokeMethod('stop');
-                      setState(() {
-                        timerRunning = false;
-                      });
                     },
                     child: const Icon(Icons.stop),
                   )

lib/timer_page.dart

@@ -11,42 +11,19 @@ class TimerPage extends StatefulWidget {
 }
 
 class _TimerPageState extends State<TimerPage> {
-  int duration = 0;
-  int elapsed = 0;
 
-  @override
-  void initState() {
-    super.initState();
-    android.invokeMethod('getProgress').then((args) => setState(() {
-          int secondsLeft = args[0];
-          int secondsTotal = args[1];
-          elapsed = secondsTotal - secondsLeft;
-          duration = secondsTotal;
-        }));
-    Provider.of<AppState>(context, listen: false).addListener(updateTime);
-  }
-
-  @override
-  void dispose() {
-    super.dispose();
-    Provider.of<AppState>(context, listen: false).removeListener(updateTime);
+  String generateTitleText(int duration, int elapsed) {
+    final minutes = ((duration - elapsed) ~/ 60).toString().padLeft(2, '0');
+    final seconds = ((duration - elapsed) % 60).toString().padLeft(2, '0');
+    return "$minutes:$seconds";
   }
 
-  void updateTime() {
-    final appState = Provider.of<AppState>(context, listen: false);
-    setState(() {
-      int secondsLeft = appState.secondsLeft ?? 0;
-      int secondsTotal = appState.secondsTotal ?? 0;
-      elapsed = secondsTotal - secondsLeft;
-      duration = secondsTotal;
-    });
-  }
-
-  get minutes => ((duration - elapsed) ~/ 60).toString().padLeft(2, '0');
-  get seconds => ((duration - elapsed) % 60).toString().padLeft(2, '0');
-
   @override
   Widget build(BuildContext context) {
+    final appState = context.watch<AppState>();
+    final duration = appState.secondsTotal ?? 0;
+    final elapsed = (duration) - (appState.secondsLeft ?? 0);
+
     return Scaffold(
       appBar: AppBar(
         title: const Text('Timer'),
@@ -55,26 +32,22 @@ class _TimerPageState extends State<TimerPage> {
         child: Stack(
           alignment: Alignment.center,
           children: <Widget>[
-            progressWidget(context),
-            textWidget(context),
+            progressWidget(context, duration, elapsed),
+            textWidget(context, duration, elapsed),
           ],
         ),
       ),
       floatingActionButton: FloatingActionButton(
         onPressed: () {
           const platform = MethodChannel('com.presley.flexify/android');
           platform.invokeMethod('stop');
-          setState(() {
-            duration = 0;
-            elapsed = 0;
-          });
         },
         child: const Icon(Icons.stop),
       ),
     );
   }
 
-  SizedBox progressWidget(BuildContext context) {
+  SizedBox progressWidget(BuildContext context, int duration, int elapsed) {
     return SizedBox(
       height: 300,
       width: 300,
@@ -90,13 +63,13 @@ class _TimerPageState extends State<TimerPage> {
     );
   }
 
-  Column textWidget(BuildContext context) {
+  Column textWidget(BuildContext context, int duration, int elapsed) {
     return Column(
       mainAxisAlignment: MainAxisAlignment.center,
       children: <Widget>[
         const SizedBox(height: 32.0),
         Text(
-          "$minutes:$seconds",
+          generateTitleText(duration, elapsed),
           style: TextStyle(
             fontSize: 50.0,
             color: Theme.of(context).textTheme.bodyLarge!.color,
@@ -106,13 +79,7 @@ class _TimerPageState extends State<TimerPage> {
         TextButton(
           onPressed: () {
             android.invokeMethod('add');
-            setState(() {
-              if (duration == 0)
-                duration += 61; // Immediately show progress at first.
-              else
-                duration += 60;
-              if (elapsed == 0 || elapsed > duration) elapsed = 1;
-            });
+            /* TODO: Make update show immediately */
           },
           child: const Text('+1 min'),
         ),