RtSignalWatcher

The RtSignalWatcher widget provides a mechanism to rebuild a widget tree whenever a Signal within its scope changes. It acts as a listener for all Signal instances within its subtree, triggering a rebuild when any of these signals emit new values.

Caution

It is not recommended to use RtSignalWatcher with a widget tree where it may contain a considerable number of arbitrary unchecked signals. Because RtSignalWatcher will listen any signals in the widget tree, regardless of its level, this could result in needless rebuilds that negatively affect performance.

For more granular control and performance optimization, consider using RtWatcher , RtConsumer , RtSelector , BuildContext.watch , BuildContext.select instead to listen for specific states and rebuild parts of the widget tree that require it.

Syntax

RtSignalWatcher({
  Key? key,
  Widget child,
  Widget builder(BuildContext context, Widget? child),
})

Properties

• key: An optional Key to use for identifying the widget.
• child: An optional Widget that remains static while the widget tree is rebuilt. It is passed to the builder function if it is defined.
• builder : A required function that builds a widget tree based on the current state of the signals. It receives the following arguments:
  • context: The BuildContext of the RtSignalWatcher widget.
  • child: The child widget passed to RtSignalWatcher .

Usage

The following example demonstrates how to use the RtSignalWatcher widget to listen for changes in a Signal and rebuild the widget tree accordingly.

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

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

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

  @override
  Widget build(BuildContext context) {
    final count = Signal(0);

    return RtSignalWatcher(
      // This widget remains static and does not rebuild when `count` changes.
      // It is passed as a `child` to the `builder` function.
      child: Row(
        mainAxisAlignment: MainAxisAlignment.center,
        children: [
          ElevatedButton(
            child: const Icon(Icons.remove),
            onPressed: () => count.value--,
          ),
          SizedBox(width: 8),
          ElevatedButton(
            child: const Icon(Icons.add),
            onPressed: () => count.value++,
          ),
        ],
      ),
      // Rebuid the widget when `count` changes
      builder: (context, child) {
        return Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            Text("Count: $count"),
            SizedBox(height: 8),
            child!,
          ],
        );
      },
    );
  }
}

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: const Center(
        child: Counter(),
      ),
    );
  }
}

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

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: CounterView(),
    );
  }
}