Singleton in Flutter: Streamline Your Code and Optimize Performance

• General

In object-oriented programming, the singleton pattern assures that a class has only one instance and offers a universal point of access. Sometimes it’s crucial for a class to have only one instance; otherwise, your program can be forced into an odd situation to use Singleton in Flutter. For instance, you only want one instance of a class to represent your local storage, or else you risk having two out-of-synch data sources. An operating system should only have one file system for the same reason.

A creational design pattern called singleton ensures that a class has just one instance and provides a single point of access for all users. Every so often, a class must have exactly one instance in order to avoid forcing your program into an odd situation.

In other words, the singleton design pattern restricts the number of “single” instances that can be created for a class.

According to the article, the singleton design solves issues by enabling it to:

• Make sure each class has a single instance.
• simple access to a class’s single instance
• Manage how it is instantiated.
• Limit the number of occurrences
• Utilize a global variable
• To put it another way, the singleton pattern guarantees that a class is never created more than once, making it simple to access it as a global variable.

Although it appears to be a straightforward design pattern, there are many implementation difficulties with it. The Singleton pattern’s application has long been a contentious issue among Flutter app developers for their web app development work. We’ll talk about how to make a Singleton class that serves its function here:

A Singleton class can be created in one of two ways:

1. Eager Initialization
2. Lazy initialization

So, let’s go inside right away.

Eager Initialization

The easiest method for establishing a singleton class is called eager initialization. DVM loads the class, at which point an instance of the class is created (Dart Virtual Machine). When a program will always utilize an instance of this class or when constructing an instance won’t take up a lot of time or resources, it can be used.

class Singleton {

 static Singleton _instance = Singleton._();

 Singleton._();

 static Singleton get instance => _instance;

  void TestMethod() {

   print("testMethod Called");

 } 

}

Lazy Initialization

With this technique, an object is only generated when it is actually required. This could reduce resource waste. It is necessary to implement the Singleton() method, which yields an instance. The constructor is made secret to ensure that the class cannot be instantiated in any other way. The fact that the object is formed inside of a method ensures that it won’t be generated until and unless it is needed.

class Singleton {

 static Singleton? _instance;

 Singleton._internal();

 factory Singleton() => _instance ??= Singleton._internal();

 void TestMethod() {

   print("testMethod Called");

 } 

}

Pros and Cons of the Singleton

Pros:

Limit the number of instances such that each class only has one instance across the entire application.

Access a global variable from any location.

Cons:

Unit test cases needed loosely connected classes since it was difficult to test specific situations with them because they maintained a global state of variables. To solve the problem, parameterized constructors and methods that accept singleton objects should be developed.

Since it keeps the overall state across the app, it goes against the single responsibility principle.

The concept is that calling MyClass() anywhere in your code will always return the same instance of that class, with the same state, etc. The singleton pattern may be easily and flexibly implemented in Dart thanks to factory constructors.

class FileSystemManager {

  static final FileSystemManager _instance = FileSystemManager._internal();

  // using a factory is important

  // because it promises to return _an_ object of this type

  // but it doesn't promise to make a new one.

  factory FileSystemManager() {

    return _instance;

  }

  // This named constructor is the "real" constructor

  // It'll be called exactly once, by the static property assignment above

  // it's also private, so it can only be called in this class

  FileSystemManager._internal() {

    // initialization logic 

  }

  // rest of class as normal, for example:

  void openFile() {}

  void writeFile() {}

}

It will become more obvious if you take that class:

void main() {

  // This constructor calls the factory constructor,

  // which turns around and returns the static instance

  // which was initialized with the `_internal` named constructor

  // this will be true if the two instances have the same hashcode

  // (hint: they do)

  print(FileSystemManager().hashCode == FileSystemManager().hashCode);

} 

class FileSystemManager {

  static final FileSystemManager _instance = FileSystemManager._internal();

  factory FileSystemManager() {

    return _instance;

  }

  FileSystemManager._internal() {

    // initialization logic 

  }

  void openFile() {}

  void writeFile() {}

}

Conclusion

The post includes an outline of Singleton’s basic structure. This was a brief introduction on my part to user interaction singletons and their uses with Flutter.

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Frequently Asked Questions (FAQs)

1. What does singleton mean?

Fluttering Singletons. A singleton class in object-oriented programming is a class that only ever has one instance (or instance of the class) at a time. The new variable also concentrates on the first instance created after the initial attempt to start the Singleton class.

2. What differentiates singleton flutter from factory flutter?

The Singleton pattern guarantees that there is only one instance of the class, and it often offers a well-known, or global, point of access. In most cases, the Factory pattern abstracts the decision of which class to instantiate and defines an interface for producing objects (with no restriction on the number).

3. Define Lazy singleton in a flutter.

However, the term “LazySingleton” designates a class whose resource will not be initialized until it is used for the first time. Typically, it is used to conserve memory and resources.

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Written by Abhishek Dhanani

Abhishek Dhanani, a skilled software developer with 3+ years of experience, masters Dart, JavaScript, TypeScript, and frameworks like Flutter and NodeJS. Proficient in MySQL, Firebase, and cloud platforms AWS and GCP, he delivers innovative digital solutions.