BuildContext.use

BuildContext.use is a method that gets an instance of T dependency from the nearest ancestor provider( RtProvider or RtComponent ) of type T .

Syntax & description

T context.use<T>([String? id]);

• context: The BuildContext object, which provides information about the current widget in the tree.
• T : The type of the dependency you want to access. These are some points to consider:
  • If the type is nullable, the method will return null if the dependency is not found.
  • If the type is not nullable, the method will throw an exception if the dependency is not found.
• id: An optional identifier for the T dependency. If omitted, the dependency will be located by its type( T ).

Usage

This following example demonstrates how to use BuildContext.use :

• counter.dart
• counter_view.dart
• counter_controller.dart
• main.dart

import 'package:flutter/material.dart';
import 'package:flutter_reactter/flutter_reactter.dart';
import 'counter_controller.dart';

class Counter extends StatelessWidget {
  const Counter({Key? key, this.id}) : super(key: key);

  final String? id;

  @override
  Widget build(BuildContext context) {
    // Locale the `CounterController` dependency
    final counterController = context.use<CounterController>(id);

    return Row(
      mainAxisSize: MainAxisSize.min,
      children: [
        ElevatedButton(
          onPressed: counterController.decrement,
          child: const Icon(Icons.remove),
        ),
        const SizedBox(width: 8),
        // Observe the `count` property of the `counterController`
        // and rebuild the widget tree when the `count` value changes
        Builder(
          builder: (context) {
            if (id != null) {
              context.watchId<CounterController>(id!, (inst) => [inst.count]);
            } else {
              context.watch<CounterController>((inst) => [inst.count]);
            }

            return Text("${counterController.count}");
          },
        ),
        const SizedBox(width: 8),
        ElevatedButton(
          onPressed: counterController.increment,
          child: const Icon(Icons.add),
        ),
      ],
    );
  }
}

import 'package:flutter/material.dart';
import 'counter.dart';

class CounterView extends StatelessWidget {
  const CounterView({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text("Counter"),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            const Counter(),
            const SizedBox(height: 8),
            FutureBuilder(
              future: Future.delayed(Duration(seconds: 1)),
              builder: (context, snapshot) {
                if (snapshot.connectionState != ConnectionState.done) {
                  return const CircularProgressIndicator();
                }

                return const Counter(id: "counterLazy");
              },
            ),
          ],
        ),
      ),
    );
  }
}

import 'package:reactter/reactter.dart';

class CounterController {
  // Create a reactive state using the `Signal` class
  final count = Signal(0);

  void increment() {
    count.value++;
  }

  void decrement() {
    count.value--;
  }
}

import 'package:flutter/material.dart';
import 'package:flutter_reactter/flutter_reactter.dart';
import 'counter_controller.dart';
import 'counter_view.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: RtMultiProvider(
        [
          RtProvider(() => CounterController()),
          RtProvider.lazy(() => CounterController(), id: 'counterLazy'),
        ],
        child: CounterView(),
      ),
    );
  }
}

In this example, the Counter widget uses BuildContext.use to get the instance of CounterController from the nearest ancestor provider(located in main.dart).