live_cell_extension 0.5.8

Generates cell property accessors for classes annotated with CellExtension from the live_cells package.

This package provides a code generator which generates extensions on ValueCell and MutableCell, from the live_cells package, that provide accessors for the properties of classes annotated with CellExtension.

Features

• Extends ValueCell and MutableCell with accessors for annotated class.

• Options for whether to generate MutableCell accessors or not.

• Allows you to write the following:

  final prop = cell.prop;
  

  instead of:

  final prop = ValueCell.computed(() => cell().prop);
  

• Allows you to write the following:

  final prop = cell.prop;
  

  instead of:

  final prop = MutableCell.computed(() => cell().prop, (value) {
    cell.value = MyClass(prop: value);
  });
  

Getting started

To use this package you'll need to add the following to the dependencies of your pubspec.yaml:

dependencies:
  live_cells_core: ^0.15.0
  ...

You'll also need to add this package and build_runner to the dev_dependencies of your pubspec.yaml:

dev_dependencies:
  build_runner:
  live_cell_extension: ^0.4.5
  ...

See the example in the example directory for an example of how to setup your project.

Usage

Annotate your classes with CellExtension() from the live_cells package:

import 'package:live_cells/live_cells.dart';

part 'person.g.dart';

@CellExtension()
class Person {
  final String firstName;
  final String lastName;
  final int age;
  
  String get fullName => '$firstName $lastName';
  
  const Person({
    this.firstName,
    this.lastName,
    this.age
  });
}

Then run the following command:

flutter pub run build_runner build

This will generate an extension for ValueCell<Person>, called PersonCellExtension which provides accessors for the properties of the Person class:

• firstName
• lastName
• age
• fullName

This allows you to access properties of Person objects held in a cell.

For example, you have a ValueCell holding a Person:

final ValueCell<Person> person;

The properties of the Person held in the cell can be accessed directly using:

final firstName = person.firstName;
final lastName = person.lastName;
final fullName = person.fullName;
final age = person.age;

Each generated property, of the generated ValueCell extension, returns a ValueCell that accesses the value of the property of the instance of the class held in the cell, on which the property is referenced. The returned ValueCell's are computed cells which update their own values whenever the values of the referenced properties of the instance change.

person.firstName is roughly equivalent to the following:

ValueCell.computed(() => person().firstName);

Example:

ValueCell.watch(() {
  print('Person ${person.fullName()} - ${person.age()}');
});

// Prints: Person John Smith - 25
person = Person(firstName: 'John', lastName: 'Smith', age: 25);

// Prints: Person Jane Doe - 30
person = Person(firstName: 'Jane', lastName: 'Doe', age: 30);

NOTE:

• Only accessors for public properties are generated.

• Only accessors for final properties and properties without a setter are generated.

  This restriction exists because modifying a non final property directly on the instance will not notify the observers of the cells created using the generated properties, which may lead to confusion.

  To allow modifying individual properties use CellExtension(mutable: true) more on this in the next section.

• The properties of the class must not have the same name as an existing property on ValueCell provided by the live_cells package. Accessors are not generated for such properties.

Mutable properties

When a class is annotated with CellExtension(mutable: true) an extension on MutableCell is also generated. The generated extension is like the extension generated for ValueCell but the generated property accessors return MutableCell's instead of ValueCell's. This allows individual properties to be modified via the MutableCell's.

Using the class from the previous example:

import 'package:live_cells/live_cells.dart';

part 'person.g.dart';

@CellExtension(mutable: true)
class Person {
  final String firstName;
  final String lastName;
  final int age;
  
  String get fullName => '$firstName $lastName';
  
  const Person({
    this.firstName,
    this.lastName,
    this.age
  });
}

Accessors for the following properties will be generated:

• firstName
• lastName
• age

Each generated accessor returns a MutableCell which when set, set's the value of the property. NOTE, this does not actually modify the instance held in the cell on which the property was accessed but creates a new instance, using the class's unnamed constructor, and assigns the cell's value to it.

Example:

final person = MutableCell(Person(firstName: 'John', lastName: 'Smith', age: 25));

ValueCell.watch(() {
  print('Person ${person.fullName()} - ${person.age()}');
});

// Prints: Person John Smith 30
person.age.value = 30;

// Prints: Person Jane Doe 30
MutableCell.batch(() {
  person.firstName.value = 'Jane';
  person.lastName.value = 'Doe';
});

NOTE:

1. The restriction on the properties being final or without a setter still applies.

   mutable: true allows the property values to be set via the MutableCell's returned by the properties of the generated extension, however directly modifying a property on the instance will not notify the observers of the cell even if mutable: true is provided in the annotation.

2. MutableCell accessors are generated only for properties for which there is a field formal parameter in the unnamed constructor of the class. That's why an accessor for fullName is not generated.

3. A ValueCell extension is still generated even when mutable: true is given. That's why in the above you can still access the fullName property directly on the cell and observe it, but you cannot set its value directly as you can for firstName, lastName and age.

4. The properties of the class must not have the same name as an existing property on either ValueCell or MutableCell provided by the live_cells package. Accessors are not generated for such properties.

Options

The CellExtension annotation also takes the following options:

• name

  The name of the ValueCell extension to generate. If this is null, the name of the generated extension is the name of the annotated class followed by CellExtension.

• mutableName

  The name of the MutableCell extension to generate, if mutable is true. If this is null, the name of the generated extension is the name of the annotated class followed by MutableCellExtension.

Additional information

Check the example in the example/ directory for a complete example from setting up the project's dependencies to a demonstration of the generated property accessors.

If you discover any issues or have any feature requests, please open an issue on the package's Github repository.