Flutter数据不可变集合插件freezed_collection的使用

Flutter数据不可变集合插件freezed_collection的使用

freezed_collection 是一个扩展 freezed 的库，它提供了深度集合的 copyWith 功能。通过该库，你可以更方便地操作不可变的数据结构。

特性

• ✅ FreezedList<T>.fromJson
• ✅ FreezedList<T>.copyWith.replaceFirst(T newElement, bool Function(T element) what)

示例

import 'package:freezed_annotation/freezed_annotation.dart';
import 'package:freezed_collection/freezed_collection.dart';

part 'one.freezed.dart';

@freezed
class One with _$One {
  const factory One(String name, Two two) = _One;

  // 从JSON解析
  factory One.fromJson(Map<String, dynamic> json) => _$OneFromJson(json);
}

@freezed
class Two with _$Two {
  const factory Two(String name, FreezedList<Three> threes) = _Two;

  // 从JSON解析
  factory Two.fromJson(Map<String, dynamic> json) => _$TwoFromJson(json);
}

@freezed
class Three with _$Three {
  const factory Three(String name) = _Three;

  // 从JSON解析
  factory Three.fromJson(Map<String, dynamic> json) => _$ThreeFromJson(json);
}

void test() {
  // 初始化数据
  final var1 = One('1', Two('2', FreezedList([Three('31'), Three('32'), Three('33')])));
  final var2 = One('1', Two('2', FreezedList([Three('31'), Three('32'), Three('33')])));
  final var21 = var2.copyWith();

  // 比较var1与var2及var21
  expect(var1, equals(var2));
  expect(var1, equals(var21));

  // 修改var21中的某些值
  final var3 = var21.copyWith
      .two(name: '21')
      .copyWith
      .two
      .threes
      .replaceFirst(Three('XXX'), (element) => element.name == '31');

  // 验证修改后的结果
  expect(var3, isNot(var21));

  // 进一步修改var3
  final var4 = var3.copyWith
      .two(name: '2')
      .copyWith
      .two
      .threes
      .replaceFirst(Three('31'), (element) => element.name == 'XXX');

  // 验证最终结果
  expect(var4, equals(var21));
}

示例代码

import 'package:freezed_collection/freezed_collection.dart';

import 'dart:convert';

import 'assistant.dart';
import 'company.dart';
import 'director.dart';

// 打印公司信息
void printT<T>(T company) => print(json.encode(company));

void main() {
  // 初始化公司对象
  final company = Company(
      name: '1',
      director: Director(
          name: 'director1',
          assistants: FreezedList(
              [Assistant(age: 1, name: '1'), Assistant(age: 3, name: '3')])));

  // 将公司对象转换为JSON字符串，并重新解析
  final jsonString = json.encode(company);
  final restoredCompany = Company.fromJson(json.decode(jsonString));

  // 打印恢复后的公司信息
  print(restoredCompany);

  // 创建新的公司对象，替换第一个年龄为1的助手
  Company? newCompany = company.copyWith.director.assistants.replaceFirstWhere(
    Assistant(age: 2, name: '2'),
    (element) => element.age == 1,
  );

  // 创建另一个新的公司对象，替换第一个年龄为2的助手
  Company? newCompany2 =
      newCompany.copyWith.director.assistants.replaceFirstWhere(
    Assistant(age: 1, name: '1'),
    (element) => element.age == 2,
  );

  // 打印原始公司、新公司及其进一步修改后的公司
  printT(company);
  printT(newCompany);
  printT(newCompany2);

  // 验证新公司是否等于原始公司
  print('Is newCompany equal to company? ${newCompany == company}');
  print('Is newCompany equal to company? ${newCompany2 == company}');
}