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add simple example on how to listen other providers #3871

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add simple example on how to listen other providers #3871

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125 changes: 125 additions & 0 deletions website/docs/essentials/listen_other_providers.mdx
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Original file line number Diff line number Diff line change
@@ -0,0 +1,125 @@
---
title: listen other providers
version: 1
---

import { Link } from "/src/components/Link";
import { AutoSnippet, When } from "/src/components/CodeSnippet";

```dart
import 'package:flutter/material.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';

void main() {
runApp(const ProviderScope(child: MyApp()));
}

final minutesProvider = NotifierProvider<MinutesNotifer, int>(() {
return MinutesNotifer();
});

final secondProvider = NotifierProvider<SecondsNotifer, int>(() {
return SecondsNotifer();
});
Comment on lines +17 to +23
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⚠️ Potential issue

Fix typo in class names

There's a typo in the class names: MinutesNotifer and SecondsNotifer should be MinutesNotifier and SecondsNotifier (missing 'i' in "Notifier").

-final minutesProvider = NotifierProvider<MinutesNotifer, int>(() {
-  return MinutesNotifer();
+final minutesProvider = NotifierProvider<MinutesNotifier, int>(() {
+  return MinutesNotifier();
});

-final secondProvider = NotifierProvider<SecondsNotifer, int>(() {
-  return SecondsNotifer();
+final secondProvider = NotifierProvider<SecondsNotifier, int>(() {
+  return SecondsNotifier();
});
📝 Committable suggestion

‼️ IMPORTANT
Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

Suggested change
final minutesProvider = NotifierProvider<MinutesNotifer, int>(() {
return MinutesNotifer();
});
final secondProvider = NotifierProvider<SecondsNotifer, int>(() {
return SecondsNotifer();
});
final minutesProvider = NotifierProvider<MinutesNotifier, int>(() {
return MinutesNotifier();
});
final secondProvider = NotifierProvider<SecondsNotifier, int>(() {
return SecondsNotifier();
});


class MinutesNotifer extends Notifier<int> {
@override
int build() {
ref.listen(secondProvider, (prev, next) {
if (prev == 59 && next == 0) {
increment();
}
});
return 0;
}

void increment() {
var nextState = state;
nextState = nextState + 1;
if (nextState == 60) {
nextState = 0;
}
state = nextState;
}
}

class SecondsNotifer extends Notifier<int> {
@override
int build() {
return 0;
}

void increment() {
var nextState = state;
nextState = nextState + 1;
if (nextState == 60) {
nextState = 0;
}
state = nextState;
}

int value() {
return state;
}
}
Comment on lines +46 to +64
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🛠️ Refactor suggestion

Remove unnecessary value() method and simplify increment logic

  1. The value() method is redundant as the state can be accessed directly through the provider.
  2. The increment logic can be simplified similar to the minutes notifier.
 class SecondsNotifer extends Notifier<int> {
   @override
   int build() {
     return 0;
   }

   void increment() {
-    var nextState = state;
-    nextState = nextState + 1;
-    if (nextState == 60) {
-      nextState = 0;
-    }
-    state = nextState;
+    state = (state + 1) % 60;
   }

-  int value() {
-    return state;
-  }
 }
📝 Committable suggestion

‼️ IMPORTANT
Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

Suggested change
class SecondsNotifer extends Notifier<int> {
@override
int build() {
return 0;
}
void increment() {
var nextState = state;
nextState = nextState + 1;
if (nextState == 60) {
nextState = 0;
}
state = nextState;
}
int value() {
return state;
}
}
class SecondsNotifer extends Notifier<int> {
@override
int build() {
return 0;
}
void increment() {
state = (state + 1) % 60;
}
}


class MyApp extends StatelessWidget {
const MyApp({super.key});

@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
colorScheme: ColorScheme.fromSeed(seedColor: Colors.deepPurple),
useMaterial3: true,
),
home: const MyHomePage(),
);
}
}

class MyHomePage extends ConsumerWidget {
const MyHomePage({super.key});

@override
Widget build(BuildContext context, WidgetRef ref) {
var secondsNotifer = ref.watch(secondProvider.notifier);
var nbMinutes = ref.watch(minutesProvider);
return Scaffold(
appBar: AppBar(
backgroundColor: Theme.of(context).colorScheme.inversePrimary,
title: const Text('The manual Clock'),
),
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
const Text(
'press the button to add seconds to the clock:',
),
Text(
'${ref.watch(secondProvider)}',
style: Theme.of(context).textTheme.headlineMedium,
),
if (nbMinutes != 0)
const Text(
'number of minutes:',
),
if (nbMinutes != 0)
Text(
'$nbMinutes',
style: Theme.of(context).textTheme.headlineMedium,
),
],
),
),
floatingActionButton: FloatingActionButton(
onPressed: secondsNotifer.increment,
tooltip: 'Increment',
child: const Icon(Icons.add),
),
);
}
}
```
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