Fix timer button negative countdown bug and enhance example app

packages/timer_button/example/lib/app.dart

@@ -0,0 +1,19 @@
+import 'package:flutter/material.dart';
+
+import 'home_page.dart';
+import 'theme.dart';
+
+class TimerButtonApp extends StatelessWidget {
+  const TimerButtonApp({super.key});
+
+  @override
+  Widget build(BuildContext context) {
+    return MaterialApp(
+      title: 'Timer Button Demo',
+      theme: AppTheme.light,
+      darkTheme: AppTheme.dark,
+      home: const HomePage(),
+      debugShowCheckedModeBanner: false,
+    );
+  }
+}

packages/timer_button/example/lib/home_page.dart

@@ -0,0 +1,70 @@
+import 'dart:developer';
+
+import 'package:flutter/material.dart';
+import 'package:timer_button/timer_button.dart';
+
+class HomePage extends StatelessWidget {
+  const HomePage({super.key});
+
+  @override
+  Widget build(BuildContext context) {
+    final colorScheme = Theme.of(context).colorScheme;
+
+    return Scaffold(
+      appBar: AppBar(
+        title: const Text('Timer Button Demo'),
+        centerTitle: true,
+      ),
+      body: Center(
+        child: Padding(
+          padding: const EdgeInsets.all(16.0),
+          child: Column(
+            mainAxisAlignment: MainAxisAlignment.spaceEvenly,
+            children: <Widget>[
+              TimerButton(
+                label: 'Try Again',
+                timeOutInSeconds: 5,
+                onPressed: () {
+                  log('Time for some action!');
+                },
+              ),
+              TimerButton(
+                label: 'Outlined: Try Again',
+                timeOutInSeconds: 5,
+                onPressed: () {},
+                buttonType: ButtonType.outlinedButton,
+                disabledColor: colorScheme.error,
+                color: colorScheme.primary,
+                activeTextStyle: TextStyle(color: colorScheme.primary),
+                disabledTextStyle: TextStyle(color: colorScheme.error),
+              ),
+              TimerButton(
+                label: 'Text: Try Again',
+                timeOutInSeconds: 5,
+                onPressed: () {
+                  log('Time for some action!');
+                },
+                timeUpFlag: true,
+                buttonType: ButtonType.textButton,
+                disabledColor: colorScheme.errorContainer,
+                color: colorScheme.primaryContainer,
+              ),
+              TimerButton.builder(
+                builder: (context, timeLeft) {
+                  return Text(
+                    'Custom: $timeLeft',
+                    style: TextStyle(color: colorScheme.tertiary),
+                  );
+                },
+                onPressed: () {
+                  log('Time for some action!');
+                },
+                timeOutInSeconds: 5,
+              ),
+            ],
+          ),
+        ),
+      ),
+    );
+  }
+}

packages/timer_button/example/lib/main.dart

@@ -1,94 +1,5 @@
-import 'dart:developer';
-
 import 'package:flutter/material.dart';
-import 'package:timer_button/timer_button.dart';
-
-void main() => runApp(const MyApp());
-
-class MyApp extends StatelessWidget {
-  const MyApp({super.key});
-
-  @override
-  Widget build(BuildContext context) {
-    return MaterialApp(
-      title: 'Timer Button Demo',
-      theme: ThemeData(
-        primarySwatch: Colors.blue,
-      ),
-      home: const MyHomePage(),
-      debugShowCheckedModeBanner: false,
-    );
-  }
-}
-
-class MyHomePage extends StatefulWidget {
-  const MyHomePage({super.key});
 
-  @override
-  MyHomePageState createState() {
-    return MyHomePageState();
-  }
-}
+import 'app.dart';
 
-class MyHomePageState extends State<MyHomePage> with TickerProviderStateMixin {
-  @override
-  Widget build(BuildContext context) {
-    return Scaffold(
-      appBar: AppBar(
-        title: const Text('Timer Button Demo'),
-      ),
-      body: Material(
-        child: Center(
-          child: Padding(
-            padding: const EdgeInsets.all(8.0),
-            child: Column(
-              mainAxisAlignment: MainAxisAlignment.spaceEvenly,
-              children: <Widget>[
-                TimerButton(
-                  label: "Try Again",
-                  timeOutInSeconds: 5,
-                  onPressed: () {
-                    log("Time for some action!");
-                  },
-                ),
-                TimerButton(
-                  label: "Outlined: Try Again",
-                  timeOutInSeconds: 5,
-                  onPressed: () {},
-                  buttonType: ButtonType.outlinedButton,
-                  disabledColor: Colors.deepOrange,
-                  color: Colors.green,
-                  activeTextStyle: const TextStyle(color: Colors.yellow),
-                  disabledTextStyle: const TextStyle(color: Colors.pink),
-                ),
-                TimerButton(
-                  label: "Text: Try Again",
-                  timeOutInSeconds: -5,
-                  onPressed: () {
-                    log("Time for some action!");
-                  },
-                  timeUpFlag: true,
-                  buttonType: ButtonType.textButton,
-                  disabledColor: Colors.deepOrange,
-                  color: Colors.green,
-                ),
-                TimerButton.builder(
-                  builder: (context, timeLeft) {
-                    return Text(
-                      "Custom: $timeLeft",
-                      style: const TextStyle(color: Colors.red),
-                    );
-                  },
-                  onPressed: () {
-                    log("Time for some action!");
-                  },
-                  timeOutInSeconds: 5,
-                ),
-              ],
-            ),
-          ),
-        ),
-      ),
-    );
-  }
-}
+void main() => runApp(const TimerButtonApp());

packages/timer_button/example/lib/theme.dart

@@ -0,0 +1,15 @@
+import 'package:flutter/material.dart';
+
+class AppTheme {
+  static ThemeData get light => ThemeData(
+        useMaterial3: true,
+        colorSchemeSeed: Colors.indigo,
+        brightness: Brightness.light,
+      );
+
+  static ThemeData get dark => ThemeData(
+        useMaterial3: true,
+        colorSchemeSeed: Colors.indigo,
+        brightness: Brightness.dark,
+      );
+}

packages/timer_button/lib/timer_button.dart

@@ -115,12 +115,15 @@ class _TimerButtonState extends State<TimerButton> with SafeStateMixin {
   int _timeCounter = 0;
   Timer? _timer;
 
+  int get _safeTimeout =>
+      widget.timeOutInSeconds < 0 ? 0 : widget.timeOutInSeconds;
+
   String get _timerText => '$_timeCounter${widget.secPostFix}';
 
   @override
   void initState() {
     super.initState();
-    _timeCounter = widget.timeOutInSeconds;
+    _timeCounter = _safeTimeout;
     _timeUpFlag = widget.timeUpFlag;
     WidgetsBinding.instance.addPostFrameCallback((_) {
       if (_timeCounter <= 0) {
@@ -139,13 +142,14 @@ class _TimerButtonState extends State<TimerButton> with SafeStateMixin {
   }
 
   void _updateTime() {
-    if (_timeUpFlag) {
+    if (_timeUpFlag || _timeCounter <= 0) {
       return;
     }
-    _timer = Timer(const Duration(seconds: aSec), () async {
+    _timer = Timer(const Duration(seconds: aSec), () {
       if (!mounted) return;
       _timeCounter--;
       if (_timeCounter <= 0) {
+        _timeCounter = 0;
         _timeUpFlag = true;
       }
       safeSetState();
@@ -157,10 +161,10 @@ class _TimerButtonState extends State<TimerButton> with SafeStateMixin {
 
   void _onPressed() {
     widget.onPressed();
-    // reset the timer when the button is pressed
     if (widget.resetTimerOnPressed) {
+      _timer?.cancel();
       _timeUpFlag = false;
-      _timeCounter = widget.timeOutInSeconds;
+      _timeCounter = _safeTimeout;
       safeSetState();
       _updateTime();
     }

packages/timer_button/test/timer_button_test.dart

@@ -562,6 +562,69 @@ void main() {
         expect(button.onPressed, isNotNull);
         expect(find.text('Negative'), findsOneWidget);
       });
+
+      testWidgets(
+          'should never display negative counter values with negative timeOutInSeconds',
+          (tester) async {
+        await tester.pumpWidget(
+          MaterialApp(
+            home: Scaffold(
+              body: TimerButton(
+                label: 'NegInput',
+                onPressed: () {},
+                timeOutInSeconds: -5,
+              ),
+            ),
+          ),
+        );
+
+        // Counter should be clamped to 0, not -5
+        expect(find.text('NegInput |  0s'), findsOneWidget);
+
+        // After frame callback, button should be enabled immediately
+        await tester.pump();
+        final button =
+            tester.widget<ElevatedButton>(find.byType(ElevatedButton));
+        expect(button.onPressed, isNotNull);
+        expect(find.text('NegInput'), findsOneWidget);
+      });
+
+      testWidgets(
+          'should clamp counter to 0 and not show negative values during countdown',
+          (tester) async {
+        int lastSeenSeconds = 999;
+        await tester.pumpWidget(
+          MaterialApp(
+            home: Scaffold(
+              body: TimerButton.builder(
+                builder: (context, seconds) {
+                  lastSeenSeconds = seconds;
+                  return Text('Time: $seconds');
+                },
+                onPressed: () {},
+                timeOutInSeconds: 2,
+              ),
+            ),
+          ),
+        );
+
+        expect(lastSeenSeconds, 2);
+
+        // Tick past the timeout
+        await tester.pump(const Duration(seconds: 1));
+        await tester.pump();
+        expect(lastSeenSeconds, 1);
+
+        await tester.pump(const Duration(seconds: 1));
+        await tester.pump();
+        expect(lastSeenSeconds, 0);
+
+        // Pump additional seconds — counter should stay at 0
+        await tester.pump(const Duration(seconds: 1));
+        await tester.pump();
+        expect(lastSeenSeconds, 0);
+        expect(lastSeenSeconds >= 0, isTrue);
+      });
     });
   });