select_when 1.0.1+1

A Flutter Provider extension: `selectWhen` to control when a selector should be invoked

SelectWhenContext Extension for Flutter

select_when_context is a Flutter extension that enhances the functionality of the Provider package by adding a selectWhen method to BuildContext. This new method offers greater control over widget rebuilds by allowing you to specify conditions that dictate when a particular selector should be invoked, helping you avoid unnecessary UI updates.

Features

• Conditional Rebuilds: selectWhen enables widgets to rebuild only under specific conditions, helping you optimize performance by reducing unnecessary updates.
• Improved Control: By specifying a when predicate, you can control when the selector should be used to compute a value, preventing unwanted recomputation.
• Similar API to select: The extension builds on the familiar select method from the Provider package, making it easy to integrate into your existing codebase.

Installation

Add the following to your pubspec.yaml:

dependencies:
  select_when_context: ^1.0.0

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Then run:

flutter pub get

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Usage

The selectWhen extension adds a method to BuildContext that allows for efficient state management in your widgets. It is particularly useful for widgets that rely on frequently updating values but only need to rebuild under certain conditions.

Example

Suppose you have a Person model with a name and an isLoading flag:

class Person with ChangeNotifier {
  String name;
  bool isLoading;

  Person({required this.name, this.isLoading = false});

  // Add logic to update `name` and `isLoading`
}

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You can use selectWhen in the build method of a widget to rebuild it only when the name changes and isLoading is false:

import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
import 'package:select_when_context/select_when_context.dart';

class PersonWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final name = context.selectWhen<Person, String>(
      (person) => person.name,
      when: (person) => !person.isLoading,
    );

    return Text(name);
  }
}

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In this example, the widget rebuilds only if the Person's name changes and isLoading is false. This provides an efficient way to control when a widget should update, reducing unnecessary rebuilds.

Key Benefits

• Performance Optimization: By controlling when the selector function is executed, you can prevent excessive and unnecessary widget rebuilds.
• Easier State Management: selectWhen is intuitive to use, similar to the standard select method, but with added flexibility via conditional rebuilds.

API Reference

selectWhen<T, R>

selectWhen is an extension method on BuildContext:

R selectWhen<T, R>(
  R Function(T value) selector, {
  required bool Function(T value) when,
})

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• selector: A function that extracts a value of type R from the provider of type T.
• when: A predicate function that returns true or false depending on whether the selector should be invoked.

Important Notes

• Use Only in build Method: selectWhen should only be used inside the build method of a widget. It will not work in other lifecycle methods like State.didChangeDependencies.
• Efficient Predicate Evaluation: The when predicate is evaluated synchronously when a provider emits an update. If it returns true, the selector is invoked and the result is compared to the previous value to determine if a rebuild is needed.

Full Example

Consider the following scenario for efficient widget updates:

import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
import 'package:select_when_context/select_when_context.dart';

class Person with ChangeNotifier {
  String name;
  bool isLoading;

  Person({required this.name, this.isLoading = false});

  void updateName(String newName) {
    name = newName;
    notifyListeners();
  }

  void setLoading(bool loading) {
    isLoading = loading;
    notifyListeners();
  }
}

class ExampleWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final name = context.selectWhen<Person, String>(
      (person) => person.name,
      when: (person) => !person.isLoading,
    );

    return Text(name);
  }
}

void main() {
  runApp(
    ChangeNotifierProvider(
      create: (context) => Person(name: 'John Doe'),
      child: MaterialApp(
        home: Scaffold(
          body: ExampleWidget(),
        ),
      ),
    ),
  );
}

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Contributions

Contributions are welcome! If you encounter any bugs or have feature requests, please open an issue or submit a pull request on the GitHub repository.

License

This project is licensed under the MIT License. See the LICENSE file for more details.

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Additional Resources

• Provider Package Documentation
• Flutter Official Documentation

With selectWhen, you can gain fine-grained control over your widgets' rebuild logic, leading to better app performance and more responsive UIs. Give it a try and see how it can optimize your Flutter applications!