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Decoding Callable Classes: A Dart Specialty For Better Flutter Apps

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Nidhi Sorathiya

July 31, 2023

Nidhi Sorathiya

July 31, 2023

Flutter allows developers to craft beautiful, high-performance applications for mobile, web, and even desktop with a single codebase. Behind the versatility and performance of Flutter lies a flexible and powerful language, Dart. And mainly, the hidden gem that we focus on in this blog post is the callable class in the Dart programming language.

Importance of Callable Classes in Flutter

Callable classes in Dart elevates the functionality and extensibility of the Flutter framework. By treating classes as function objects and enabling them to be invoked like a function. Dart opens up new possibilities in the design and organization of your Flutter application’s code. Although this feature might not be extensively used in every Flutter app, understanding its potential can help you write more maintainable and advanced code.

Overview of Callable Classes

In a nutshell, a callable class in Dart is a class that can behave like a function. This feature is implemented using the call() method, letting an instance of the class be called as a function. The real power of callable classes comes into the scene when dealing with APIs, data manipulation or just making your code cleaner and more intuitive.

This snippet illustrates a basic callable class in Dart. When run, it prints 'Hello Nidhi from India'. Just as if 'object' was a function itself!

Class in Dart Programming Language

Before diving straight into the procedure of working with callable classes in Dart, it's essential to first lay down a strong foundation on classes.

‘Car’ Class with its fields and methods.
‘Car’ Class with its fields and methods.

Introduction to Object-Oriented Programming in Dart

Dart, like many modern languages, supports object-oriented programming (OOP). It makes use of features like classes and objects, inheritance, polymorphism, encapsulation, and abstraction, which helps in creating modular and maintainable code.

The above Dart code defines a class named 'Car' with properties 'model' and 'year'. We have a method named 'showCarDetails()' that prints these properties.

Understanding the Concept of Classes

In Dart, 'class' is a blueprint from which objects are created. A class encapsulates data for the object. It includes variables for storing data and methods to execute code.

Types of Classes in Dart

In Dart, the classes can be broadly categorized into the following types:

1. Regular classes

The common type of classes including members (methods or functions) and fields (variables).

2. Abstract classes

Classes that cannot be instantiated. They are often used to provide an interface for other classes.

3. Singleton classes

A special class that restricts the instantiation of a class to a single instance.

4. Callable classes

These are the classes that can be called a function, which is our main focus in this blog.

How to Define and Instantiate a Class in Dart

Defining a class in Dart comprises declaring the class, adding fields and methods to the class, and finally creating an instance of the class using the 'new' keyword.

In the above code snippet, 'Car' is a class with 'carName' and 'modelYear' as fields and a 'display()' method.

Callable Classes - A Deep Dive

Now that we have a fair understanding of classes in Dart, let's explore the main subject of this blog - Callable Classes.

Definition and Conceptualization

A callable class in Dart is a class that can be invoked as if it were a function. This invokes the class's 'call()' method, which allows an instance of the class to be called a function. This feature brings more scalability and flexibility when dealing with classes and functions in Flutter apps.

The Importance and Need of Callable Classes

Callable classes can help make your code more flexible and abstract. They allow you to handle functions dynamically throughout your code, contributing to improved maintainability. They prove particularly helpful when working with complex Widget trees in Flutter, delegating specific functional tasks, or reducing duplication of declarative code in your project.

The 'Call' Method

The 'call()' method is an essential part of a callable class. Dart allows the developer to name 'call' a method in classes and then treats that class as a function, invoking the 'call' method. Due to Dart’s mostly flexible nature for functions, developers can pass any number of parameters and invoke callable class instances just as standard functions.

In this Dart code, 'CallableClass' is a callable class that has a 'call()' method. The 'call()' method is invoked when we treat the instance of the class as a function.

Advantages of Using Callable Classes

Callable classes promote cleaner code, enhance flexibility, and feature a unified way of using functions and objects interchangeably. They are especially beneficial for event-driven programmingasynchronous tasks, manipulating live data or streams, and interacting with different APIs, making it easier, cleaner, and manageable.

Working with Callable Classes in Flutter

Understanding the theoretical aspect of callable classes is good, but let's take a step further to see how we can work with them in Flutter.

Creating your First Callable Class

The creation of a callable class corresponds to defining a class with a 'call' method. Here’s how you create a basic callable class:

In the above code, 'MultiplyTwoNumbers' is a callable class that can multiply two integers.

Using the "Call" Method

After creating a callable class, you can create a new instance of it and use it as if it were a function. Here's an example:

When you run this code, it prints 'Result: 200'. As you can see, we’re invoking 'multiply' as if it was a function.

A Step-by-step Procedure to Create a Callable Class

  1. Define a new class.
  2. As part of the class definition, include a call() method. This method can take any parameters you want.
  3. After defining the class, instantiate it.
  4. Finally, use the instance as if it were a function.

Understanding the Structure and Syntax of Callable Classes

The structure of a callable is similar to regular classes. The main difference is that it includes a 'call' method which is executed when an instance of the class is invoked as a function.

Callable Classes and the Concept of Implicit Interfaces

In Dart, every class implicitly defines an interface with all its defined instance methods. Callable classes are no different, and they define an interface with a 'call' method. This allows them to be used wherever this interface is expected.

Real-World Use Cases of Callable Classes

Now that we know how to create and use Callable Classes in Dart, let's examine where these classes can make a difference in real-world Flutter applications.

Callable Classes in Data Management

Handling large datasets and manipulating the data for rendering it on the UI is common in app development. Here, callable classes can be used to perform data manipulations, giving a cleaner and easier-to-read code.

Using Callable Classes for Handling Events in Flutter

In large Flutter applications with complex widget trees, defining handlers for events (like button presses) often requires coding repetitive logic. Callable classes can streamline this process by encapsulating the logic within a class and allowing it to be invoked as a function whenever needed.

Callable Classes in API Consumption: A Case Study

Imagine a scenario where your app interacts with various external services and each requires a different approach to handle the API's response. Here, callable classes shine by providing an intuitive way to encapsulate the logic of each API handler.

Callable Classes and Stream Manipulation

When dealing with streams of data in an app like in real-time databases or messaging apps, callable classes can be used to encapsulate the logic of stream handling, making your code cleaner, flexible and maintainable.

Advanced Concepts in Callable Classes

Having covered the basics and usage scenarios of callable classes, let's delve deeper into more sophisticated aspects and understand how 'callable class in Dart' can be taken advantage of.

Callable Classes with Multiple Parameters

While our previous examples featured callable classes with a single parameter or two, it's possible to create a class with multiple parameters or none at all.

In this Dart code, 'AdvancedCallableClass' is a callable class that has a 'call()' method capable of dealing with optional parameters.

Working with Callable Classes and Error Handling

Callable classes when used at the core level of your app, and handling functions and methods, should be carefully designed around the error or exception handling.

Callable Classes with Anonymous Functions

In Dart, callable classes can also be made to work in conjunction with anonymous functions or closures. This provides another option to make your code compact, readable, and flexible.

Callable Classes and Asynchronous Programming

Similarly, you can design callable classes to return a Future, allowing it to be await-able. This can be very handy for dealing with APIs, file handling, and any other task that needs to be handled asynchronously in Dart.

Common Pitfalls and Best Practices when Using Callable Classes

While callable classes offer enhanced flexibility, they must be used wisely. Here are some common errors you might encounter and best practices to keep in mind.

Understanding Common Errors with Callable Classes

A common mistake when working with callable classes is not defining or appropriately using the 'call' method, which results in errors. An example of a related error statement can be “Class <ClassName> has no instance method 'call'...''.

Best Practices and Conventions while writing Callable Classes

  • Always remember to define the 'call()' method in your class when you intend to use it as a callable class.
  • Use callable classes where it makes the code cleaner and easier to understand. Overuse might make your code unnecessarily complex.
  • Callable classes should ideally not be overused for the sake of just using classes as functions. They have specific use cases and should be used accordingly.

Effect of Callable Classes on Flutter Application Performance

Callable classes, if used correctly, should not affect your application's performance. Dart does a fantastic job of optimizing callable classes to where their performance is on par with regular functions. However, improper usage can complicate debugging and maintenance, so it's essential to use them judiciously.

In this example, the 'OptimizedCallableClass' shows an optimized use of a callable class. It contains the needed code to execute within it and does not contain unnecessary attributes or methods.

Conclusion and Future Perspective

We've traversed a journey understanding classes in Dart, defining callable classes, and exploring how they can be leveraged in Flutter applications. Let's summarize and reflect upon what this means for your Flutter app development and the power of the Dart language.

The Ultimate Role of Callable Classes in Flutter Apps

Callable classes serves as a powerful tool in the arsenal of Flutter developers, offering a unique way to treat classes as function objects. They not only aid in writing more flexible and efficient code but also open up novel avenues of structuring and abstracting your Flutter apps.

Future Perspective of Callable Classes in Flutter

While the concept of callable classes is not widespread at the moment, more developers recognizing its potential can change this. As the Dart language and Flutter framework evolve, we can anticipate seeing more tools, packages, and built-in support to easily work with callable classes.

Build your next app with WiseGPT!

In this blog post, we've demystified the concept of callable classes in Dart, a powerful yet underappreciated feature of this robust language. Understanding and skillfully leveraging this concept will undoubtedly make your journey with Flutter more enriched and productive.

Before you start implementing callable classes in your Flutter projects, I have a "productive" recommendation: "WiseGPT". It is a powerful plugin that will revolutionize how you handle code generation in your Flutter apps.


With WiseGPT, you can effortlessly generate code for APIs directly into your Flutter project, without worrying about output size limitations. Whether you're dealing with simple or complex API endpoints, WiseGPT has got you covered. It will automatically mirror your coding style, ensuring a seamless integration of the generated code into your existing project.

By leveraging WiseGPT in your Flutter development process, you can save valuable time and effort, allowing you to focus on other critical aspects of your app. It simplifies the entire API integration process, making it more efficient and enjoyable.

So, what are you waiting for? Give WiseGPT a try and experience the true power of automated code generation for your APIs in Flutter. With WiseGPT by your side, you can build sophisticated and feature-rich apps with ease.

Keep exploring the world of Dart and Flutter, enhancing your knowledge and skills. Thank you for joining me on this journey of exploring callable classes in Dart. I hope you found this blog insightful and that it empowers you to create stunning, powerful apps that leave a lasting impression on your users!

Frequently asked questions

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