Flutter Singleton Pattern – An Ultimate Guide in 2023

• General

In Flutter, Singleton is one of the simple and easy design patterns. Of course, this programming technique saves memory and offers an ideal solution to some instances. As a Flutter programmer, you must understand the requirements first.

What is Flutter Singleton?

As a real-world analogy, Let’s consider the analogy of a company’s CEO. You see, in a given company, there can be only one CEO, regardless of who holds the position at any given time. The title “the CEO of CompanyX” serves as a global identifier, providing a single point of access to represent or reference the individual in charge of the company.

Of course, the Flutter singleton class has a single instance and gives access points to it. As a developer, you must control initialization and keep track of the sole process. Hence, it has limits and the instantiation of a class should be noted down with one object as well. The purpose of using singleton is to access an object with dynamic parts of the program. 

Classes have to be established with one instance of the operating system. It must have one file system and one local storage. They capture well and are mainly applicable for holding certain elements for object-oriented software. So, it should be identified with singleton and often create reusable object-oriented software approaches. 

Let’s look at this by simple example,

class CEO {
  final String name;
  final String company;

  CEO._({this.name, this.company});
  static CEO _instance;

  static CEO getInstance({String name, String company}) {
    if (_instance == null) {
      _instance = CEO._(name: name, company: company);
      return _instance;
    }
    return _instance;
  }
}

void main() {
  print(CEO.getInstance(name: "John Doe", company: "CompanyX").name); // Output: John Doe
  print(CEO.getInstance().name); // Output: John Doe
}

Dart Singleton Implementation

The factory instructor should be identified with the right implementation techniques. It includes singleton in dart by focusing on easy and flexible options. They make sure to obtain class initiated by file by characterized results. 

Here is how the Singleton design pattern is implemented in Dart:

• Singleton with Factory Constructor

class SingletonStaticFG {

  SingletonStaticFG._privateConstructor();

  static final SingletonStaticFG _instance = SingletonStaticFG._privateConstructor();

  static SingletonStaticFG get instance => _instance;
  
}

• Dart Singleton with static getter

class SingletonStaticFG {

  SingletonStaticFG._privateConstructor();

  static final SingletonStaticFG _instance = SingletonStaticFG._privateConstructor();

  static SingletonStaticFG get instance => _instance;
  
}

• Dart Singleton with static field

class SingletonStaticField {

  SingletonStaticField._privateConstructor();

  static final SingletonStaticField instance = SingletonStaticField._privateConstructor();
  
}

And all these three you can initilize like this way:

SingletonFactory field = SingletonFactory();
SingletonStaticFG fgField = SingletonStaticFG.instance;
SingletonStaticField sField = SingletonStaticField.instance;

Creating a Singleton Shared Preference in Flutter

On the other hand, Flutter helps to store and maintain a secure solution and approach them with app-level data. They assign more outcomes and close depending on the share preference as a singleton dart object. They usually come to simplify many tasks. In addition to this, it explores closing apps without creating share preferences. 

class Singleton {
  /// private constructor
  Singleton._();
  /// the one and only instance of this singleton
  static final instance = Singleton._();
}

Usage of DIO Singleton in Flutter

In the Flutter DIO package, the network library has to hold certain things. It includes a powerful HTTP client for Dart that supports interceptors and configuration. They guide everyone to request a cancellation and connect timeout. 

Flutter Provider Singleton

A single object is created by singleton providers. It returns the first object it created from memory on subsequent calls. In Flutter, an illustration of a Provider Singleton is as follows: Singletons are frequently an acceptable option for the design of libraries or packages, and this is a very noble objective. However, we should use them with extreme caution when writing application code because they can cause numerous issues in our codebase.

Flutter widget trees in Flutter apps are deeply nested. Singletons make it simple to access the objects we need from any widget because of this. However, singletons have a lot of problems, and there are better, but still simple alternatives.

Singleton Drawbacks

Of course, it understands the significance very well and it must be problematic. It includes common drawbacks and possible solutions. 

1. Singletons are hard to test

Using singletons makes your code hard to test.

Check out the mocktail package for more info about how to write tests using mocks.

2. Singletons are Implicit Dependencies

classFirebaseAuthRepository {
  Future<void>signOut() =>FirebaseAuth.instance.signOut();
}

In this case, it’s easy to see that FirebaseAuthRepository depends on FirebaseAuth.

However, it becomes much more challenging to identify singletons as soon as we have classes with a few dozen lines of code. However, when passed as explicit constructor arguments, dependencies are much easier to see.

In the previous example, as soon as we initialize the hardWorker variable within the main() method, all of the heavy processing code runs. We can use late to delay the object’s initialization until after it is actually used in these situations.

void main() {
  // prints nothing
  // initialization will happen later when we *use* hardWorker
late final hardWorker = HardWorker.instance;
  ...
  // initialization happens here
  // prints 'work started' from the constructor
hardWorker.logResult();
}

However, because it is so simple to forget to use it later, this method is prone to error. Dart, on the other hand, lazy-loads all global variables (as well as static class variables) by default. This indicates that they are only initialized upon initial use. Local variables, on the other hand, are initialized immediately upon declaration, unless they are declared too late. 

We can use packages like get_it instead, which make it simple to register a lazy singleton:

classHardWorker {
HardWorker._() {
    // do some heavy processing
  }
// register a lazy singleton (won't be created yet)
getIt.registerLazySingleton<HardWorker>(() =>HardWorker());
// when we need it, do this
finalhardWorker = getIt.get<HardWorker>();
And we can do the same with Riverpod, since all providers are lazy by default:
// create a provider
finalhardWorkerProvider = Provider<HardWorker>((ref) {
returnHardWorker();
});
// read the provider
finalhardWorker = ref.read(hardWorkerProvider);

In general, the object should be carried out with the first case. They carry out more things riverpod should accumulate by using providers. They include riverbed documentation about testing forever. This considers effective notice and creates the first use case for objects forever. 

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Instance Lifecycle

A singleton instance that we initialize will remain alive until the end of time (also known as soon as the application) is finished. We also cannot release the instance earlier if it uses a lot of memory or keeps a network connection open.

Riverpod and other Flutter packages, on the other hand, give us more control over when a particular instance is disposed of. Riverpod actually has a lot of intelligence and lets us easily control a provider’s lifecycle and state. We can, for instance, make use of the autoDispose modifier to guarantee that our HardWorker will be disposed of as soon as the final listener is removed.

finalhardWorkerProvider = Provider.autoDispose<HardWorker>((ref) {
returnHardWorker();
});

It carries out more options and is likely to explore unmounted Flutter designs. It should be implemented based on the language necessary options. 

Thread Safety

Accessing singletons across multiple threads in multi-threaded languages necessitates caution, and if they share mutable data, a synchronization mechanism may be required.

However, since all application code in a Flutter web app development is part of the main isolate, this typically is not a concern in Dart. However, we must exercise greater caution if separate isolates are created to carry out complex computations.

Conclusion

By reading the above scenario, you can see the complete guide about the Flutter singleton. We have witnessed Flutter singleton, Dart singleton integration, developing the singleton preference in Flutter, Flutter provider singleton, and so on. I hope you understand Flutter Singleton with an example. However, it should be vital to explore changes in singleton creation. We have a team of experienced mobile app developers. So, you can hire fluter app developers from Flutter Agency who are eligible to create a singleton and know how to integrate it into the development process and build a successful mobile application for your business.  Do not hesitate and connect us if you have queries. Share your requirements today!

Frequently Asked Questions (FAQs)

1. When should you use the singletons?

A singleton should be utilized while managing the access to resources shared by a whole application. And it will be destructive to have various instances of a similar class. Therefore, ensuring access to the shared resources thread is safe is an excellent example of where this kind of pattern can be necessary.

2. Why is singleton necessary?

It is used when a single instance of a class is needed to control an action throughout an execution. A singleton class should not have various instances in any case and at any cost. Moreover, the singleton classes are utilized for logging, database connections, driver objects, cache, and thread pool.

3. How do you secure the singleton in Flutter?

To overcome this problem, we must integrate the clone()method and throw an exception—cloneNotSupportedException from the clone method. If anyone tries to make the clone object of a singleton, it will throw an exception.

Written by Harshita Luhana

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