# Provider

> Uses the Provider package for dependency injection and state management in Flutter. Use when setting up providers, consuming state, optimizing rebuilds, using ProxyProvider, or migrating from deprecated providers. Use when this capability is needed.

- Skill: `tomevault-io/provider` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add tomevault-io/provider`
- Raw SKILL.md: https://api.skillmd.com/api/skills/tomevault-io/provider/raw
- Safety review: pending (external: skill-scanner PASS, skillspector PASS)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: tomevault-io (https://skillmd.com/u/tomevault-io)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/tomevault-io/provider

---


# Provider Skill

This skill defines how to correctly use the `provider` package in Flutter applications.

---

## 1. Provider Types

| Provider | Use for |
|---|---|
| `Provider` | Exposing any immutable value |
| `ChangeNotifierProvider` | Mutable state with `ChangeNotifier` |
| `FutureProvider` | Exposing a `Future` result |
| `StreamProvider` | Exposing a `Stream` |
| `ProxyProvider` / `ChangeNotifierProxyProvider` | Objects that depend on other providers |

---

## 2. Setup

```dart
MultiProvider(
  providers: [
    Provider<Something>(create: (_) => Something()),
    ChangeNotifierProvider(create: (_) => MyNotifier()),
    FutureProvider<String>(create: (_) => fetchData(), initialData: ''),
  ],
  child: MyApp(),
)
```

- Use `MultiProvider` to group multiple providers and avoid deeply nested trees.
- `ChangeNotifierProvider` **automatically disposes** the model when it is no longer needed.
- **Never** create a provider's object from variables that can change over time — the object won't update when the variable changes. Use `ProxyProvider` instead.
- If you have 150+ providers, consider mounting them over time (e.g., during a splash screen) rather than all at once to avoid `StackOverflowError`.

---

## 3. Consuming State

Always specify the **generic type** for type safety:

```dart
// Listen and rebuild on change
final count = context.watch<MyModel>().count;

// Access without listening (use in callbacks)
context.read<MyModel>().increment();

// Listen to only part of the state
final count = context.select<MyModel, int>((m) => m.count);
```

Use `Consumer<T>` or `Selector<T, R>` widgets when you need fine-grained rebuilds and cannot access a descendant `BuildContext`:

```dart
Consumer<MyModel>(
  builder: (context, model, child) => Text('${model.count}'),
  child: const ExpensiveWidget(), // rebuilt only once
)

Selector<MyModel, int>(
  selector: (_, model) => model.count,
  builder: (_, count, __) => Text('$count'),
)
```

---

## 4. ProxyProvider

Use `ProxyProvider` or `ChangeNotifierProxyProvider` for objects that depend on other providers or values that can change:

```dart
MultiProvider(
  providers: [
    Provider<Auth>(create: (_) => Auth()),
    ProxyProvider<Auth, Api>(
      update: (_, auth, __) => Api(auth.token),
    ),
  ],
)
```

---

## 5. Rules

- Do **not** access providers inside `initState` or constructors — use them in `build`, callbacks, or lifecycle methods where the widget is fully mounted.
- You can use **any object** as state, not just `ChangeNotifier`; use `Provider.value()` with a `StatefulWidget` if needed.

---

## 6. Debugging

Implement `toString` or `DiagnosticableTreeMixin` to improve how your objects appear in Flutter DevTools:

```dart
class MyModel with DiagnosticableTreeMixin {
  final int count;
  MyModel(this.count);

  @override
  String toString() => 'MyModel(count: $count)';
}
```

---

## 7. Migration: ValueListenableProvider

`ValueListenableProvider` is deprecated. Use `Provider` with `ValueListenableBuilder` instead:

```dart
ValueListenableBuilder<int>(
  valueListenable: myValueListenable,
  builder: (context, value, _) {
    return Provider<int>.value(
      value: value,
      child: MyApp(),
    );
  },
)
```

---

## References

- [Provider GitHub Repository](https://github.com/rrousselGit/provider)

---
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<!-- tomevault:4.0:skill_md:2026-04-16 -->