修改了@Seth Ladd关于谁更喜欢Swift风格的单例，比如。shared的答案:

class Auth {
  // singleton
  static final Auth _singleton = Auth._internal();
  factory Auth() => _singleton;
  Auth._internal();
  static Auth get shared => _singleton;

  // variables
  String username;
  String password;
}

示例:

Auth.shared.username = 'abc';

这应该有用。

class GlobalStore {
    static GlobalStore _instance;
    static GlobalStore get instance {
       if(_instance == null)
           _instance = new GlobalStore()._();
       return _instance;
    }

    _(){

    }
    factory GlobalStore()=> instance;


}

因为我不太喜欢使用new关键字或其他构造函数，比如对单例对象的调用，我更喜欢使用一个名为inst的静态getter:

// the singleton class
class Dao {
    // singleton boilerplate
        Dao._internal() {}
        static final Dao _singleton = new Dao._internal();
        static get inst => _singleton;

    // business logic
        void greet() => print("Hello from singleton");
}

使用示例:

Dao.inst.greet();       // call a method

// Dao x = new Dao();   // compiler error: Method not found: 'Dao'

// verify that there only exists one and only one instance
assert(identical(Dao.inst, Dao.inst));

实例化后不能更改对象的单例

class User {
  final int age;
  final String name;
  
  User({
    this.name,
    this.age
    });
  
  static User _instance;
  
  static User getInstance({name, age}) {
     if(_instance == null) {
       _instance = User(name: name, age: age);
       return _instance;
     }
    return _instance;
  }
}

  print(User.getInstance(name: "baidu", age: 24).age); //24
  
  print(User.getInstance(name: "baidu 2").name); // is not changed //baidu

  print(User.getInstance()); // {name: "baidu": age 24}

我在dart和之前的Swift上使用这个简单的模式。我喜欢它的简洁和只有一种使用方式。

class Singleton {
  static Singleton shared = Singleton._init();
  Singleton._init() {
    // init work here
  }

  void doSomething() {
  }
}

Singleton.shared.doSomething();

你好，这样的东西怎么样?非常简单的实现，Injector本身是单例的，并且还添加了类。当然可以很容易地扩展。如果您正在寻找更复杂的东西，请检查这个包:https://pub.dartlang.org/packages/flutter_simple_dependency_injection

void main() {  
  Injector injector = Injector();
  injector.add(() => Person('Filip'));
  injector.add(() => City('New York'));

  Person person =  injector.get<Person>(); 
  City city =  injector.get<City>();

  print(person.name);
  print(city.name);
}

class Person {
  String name;

  Person(this.name);
}

class City {
  String name;

  City(this.name);
}


typedef T CreateInstanceFn<T>();

class Injector {
  static final Injector _singleton =  Injector._internal();
  final _factories = Map<String, dynamic>();

  factory Injector() {
    return _singleton;
  }

  Injector._internal();

  String _generateKey<T>(T type) {
    return '${type.toString()}_instance';
  }

  void add<T>(CreateInstanceFn<T> createInstance) {
    final typeKey = _generateKey(T);
    _factories[typeKey] = createInstance();
  }

  T get<T>() {
    final typeKey = _generateKey(T);
    T instance = _factories[typeKey];
    if (instance == null) {
      print('Cannot find instance for type $typeKey');
    }

    return instance;
  }
}