What is Flutter?

Flutter is a framework used to make applications with a single codebase and handle data seamlessly. It is used to make Android, Desktop, iOS, and web applications and was developed in 2017 by Google. Today, Flutter is one of the most widely used toolkits by many startups and MNCs like Google, Alibaba, and BMW to build scalable, robust, and data-efficient applications. In this guide, we will learn about Flutter, its features, installation, testing, and companies using it in detail.

Table of Contents:

• What is Flutter?
  • Features of Flutter
• What is Dart?
• Different Types of Apps
• History of Flutter
• Architecture of Flutter
• Why is Flutter a boon for Startups and Companies?
• Get Started with Flutter
• Who Uses Flutter?
• Testing the Flutter Apps
• Advantages of Flutter
• Disadvantages of Flutter
• Conclusion

What is Flutter?

Flutter is an open-source toolkit (set of tools) developed by Google to build cross-platform applications from a single codebase, i.e., you write one set of code to work on multiple platforms like Android, Windows, Mac, and Linux without rewriting it. It is not just a framework or a library, it is a complete SDK (Software Development Kit), including everything needed to build a high-performance and user-interactive application.

• A library is a reusable piece of software that performs a specific function added to your application.
• A framework provides a structure for app development and defines the architecture to complete the application.
• An SDK is much broader than both above. It is a full set of tools required for software development, including libraries, frameworks, APIs, compilers, documentation, and debugging tools.

Features of Flutter

Flutter has the following features:

• Single Codebase: Write one set of code and deploy to Android, iOS, web, desktop, and more. Flutter allows developers to use a single codebase that runs smoothly on multiple platforms, which reduces development time, effort, and cost, as there is no need to write the code for each platform.
• Own Engine: Flutter uses the Skia graphics engine to draw UI elements directly, ensuring consistent design across platforms. Unlike other frameworks that depend on the native UI components of each platform, Flutter does not depend on platform-specific OEM (Original Equipment Manufacturer) widgets; it uses Skia for its high-performance 2D graphics.
• Written in Dart: Flutter applications are written in Dart, a modern, object-oriented language developed by Google for building fast, reactive applications across various platforms.
• Widget-Based UI: In Flutter, everything is a widget, whether it is a button, padding, layout, animation, or even the entire screen. They are the building blocks of Flutter applications.
• Fast Reload: One of the most powerful features of Flutter is that instant changes made in the code are visible without losing the app’s state and without restarting the application.

What is Dart?

Dart is a modern, open-source programming language developed by Google. It is a primary language used with Flutter, designed to build fast, scalable, and reliable applications across platforms like mobile, and desktop. It is an object-oriented programming language (like Java and C++) that has features like classes, generics, interfaces, and asynchronous programming using the async and await keywords. It uses both Just-In-Time (JIT) and Ahead-Of-Time (AOT) compilation, useful in hot reload and deployment of an application.

One of the most powerful features of Dart is sound null safety, which helps to eliminate null reference errors by ensuring that variables cannot contain a null value unless they are explicitly declared, making apps more robust and less prone to crashes.

Different Types of Apps

The following types of applications are mainly supported by Flutter:

1. Android Apps

Android applications are built for Android devices, using Java or Kotlin as a programming language. These applications are packaged with an .apk extension and deployed with the help of the Google Play Store. Flutter directly compiles to ARM (Advanced RISC Machine) or x86 code, which results in faster performance, reduced latency, and smoother animations.

Flutter includes a set of Material Design widgets, which follow the design principles of Google and make the app feel native to Android users. These widgets are customizable and can be used to create both standard and complex UIs. Developers can also use GPS, camera, sensors, file system, and Bluetooth using built-in plugins or by writing platform-specific code using platform channels, which allows Dart code to communicate with Java/Kotlin natively.

2. iOS Apps

Flutter also supports building iOS apps using the same code to build Android applications and other platforms. Flutter lets you write a single set of code in Dart, and that works for both iOS and Android. It compiles your code into native machine code, so that the application runs fast on iPhones and iPads. To make the app look like an iOS app, Flutter provides special UI widgets called Cupertino widgets, which follow the design style of Apple.

3. Desktop Apps

Flutter is used to build desktop applications for Windows, macOS, and Linux, i.e., you can use the same Dart code that you used for mobile applications to create apps that run on computers. These desktop applications are not web-based, they are real applications that can open in their own windows and support keyboard and mouse like any other application you install on your own computer.

4. Web Apps

Flutter is also used to build web applications using the same Dart code you used to build Android, iOS, or desktop applications. These web apps can run in any modern web browser like Chrome, Firefox, Safari, or Edge, without installing anything. When you build a Flutter web app, your Dart code gets compiled into JavaScript and works like any normal website.

History of Flutter

Flutter was introduced in May 2017, during the Google I/O developer conference, as a beta version to test and contribute to it worldwide. At first, it gained popularity due to its hot reload feature, modern Dart language, and widget library that created attractive UIs. After a year, Flutter reached its first stable release on December 4, 2018, with its first version, Flutter 1.0, at the Flutter Live event in London. In 2019, Google announced Flutter for web, allowing developers to run Flutter applications via web browsers. Later, support for desktop platforms like Windows, macOS, and Linux was introduced, making Flutter a universal framework.

Traditionally, the companies had to write the code separately for the iOS and Android devices. But, with the help of Flutter, a single codebase is used to build the applications for desktop, Android, iOS, and web Applications. Today, Flutter is used by thousands of developers and major brands like Google Pay, Alibaba, BMW, eBay, ByteDance (TikTok), and many others.

Architecture of Flutter

Below is the detailed architecture of Flutter with its working.

1. Framework Layer(Dart)

The Framework Layer is the top section in the above image and serves as an entry point for Flutter developers. It provides the tools, widgets, and structure needed to build UIs using the Dart programming language and interacts with the low-level APIs.

Now, let us discuss the components present in the Framework layer.

a. Material and Cupertino

The two widgets, Material and Cupertino, are present at the top in the Framework layer.

• Material is the widgets that implement Google’s Material Design, the design standard for Android apps. It is used to create a platform-specific application, so that UI features of the apps are according to the platform it is made for. For example, Scaffold, AppBar, etc.
• Cupertino widgets mimic the iOS Human Interface Guidelines. For example, CupertinoButton, CupertinoNavigationBar.

b. Widgets

This layer is present below the Material and Cupertino layers. They are the core building blocks of any Flutter UI, and everything from styling to components is a widget. For example, text, column, row, container, etc.

Note: Everything in a widget is stored in a tree-like structure, known as the widget tree.

In Flutter, there are three main types of widgets present. These are

• Stateless Widgets: A Stateless Widget is a type of widget in Flutter that does not store or manage any internal state after it is built. It means that once this widget is created, it cannot change its behaviour or appearance dynamically when the application is running. It is used when your UI is static and does not depend on any changes or data updates.
• Stateful Widgets: A Stateful Widget is a type of Widget in Flutter that can hold and manage its internal state, which can be changed in the future. This allows the widget to dynamically update its appearance or behaviour in response to events like user interactions, updates of any type of data, animations, etc.
• Inherited Widgets: An Inherited Widget is a special type of Widget in Flutter used to pass data down the widget tree efficiently. It allows child widgets to access the shared data without manually passing it through constructors or maintaining its global state.

c. Rendering

After Widgets, the layer called rendering is present, responsible for converting the widget tree into a render tree, calculating layouts, and visual effects. Rendering begins before the Skia graphics engine starts to draw the UI elements and ensures that the UI structure built by widgets is displayed accurately on the screen.

There are three layers present below the rendering layer, which are Animation, Painting, and Gestures.

d. Animation

Animation is present on the leftmost block below the rendering layer and is used to enhance the user experience by making the application feel smoother, interactive, and natural. It includes classes like Animation, AnimationController, Tween, and more, enabling developers to add rich visual effects and transitions, like page transitions, fading, rotating elements, and so on.

e. Painting

Painting is present in the middle block below the rendering layer, responsible for drawing visual elements like lines, texts, shapes, images, etc, on the screen. It works on a canvas-like model and converts layout information into pixels, once the size and position of the widget are finalized. You can use the CustomPaint() and CustomPainter() methods to draw custom graphics.

f. Gestures

Gestures are the rightmost block below the rendering layer, and recognize user inputs such as touch and pointer interactions like tap, double tap, drag, long press, etc, to enable interactive functionality.

g. Foundation

The foundation is the last layer present in the Framework Layer. It provides essential building blocks and utilities for the rest of the framework, and does not deal with UI directly, but everything above it depends on it to supply low-level APIs, state management, and debugging.

2. Engine(C++)

The engine layer is the core powerhouse of Flutter, implemented in C++ and C. It provides the runtime capability that makes the application fast and smooth. The Engine uses Skia to paint pixels on the screen and handles text layouts, text rendering, and so on through libraries like Harfbuzz. It acts as a bridge between the Dart Framework Layer and the Platform Embedder Layer.

Now, let us discuss the components present in the Engine layer.

a. Service Protocol

The Service Protocol is a set of APIs used to enable communication between a running Flutter (or Dart) app and developer tools like Flutter DevTools, Debugger, and Hot Reload. It acts as a bridge between the Flutter runtime and external development tools, and enables real-time feedback and interactivity during development.

For example, when you press hot reload in VS Code or Android Studio, the Dart Code is recompiled, and the Service Protocol sends the update to the Flutter running application, and the app updates without restarting and losing its UI state.

b. Composition

Composition is a process of taking all your widgets and layering them together to create a final screen. It makes the app smooth, fast, and avoids redrawing of things that did not change in the code, before the final output is drawn on the screen.

c. Platform Channels

Platform Channels allow Flutter apps to communicate with the hardware features and native code, like Kotlin/Java on Android and Swift/Objective-C on iOS, that are not built into Flutter by default. It enables access to the device-specific features that Dart alone cannot handle. For example, to open a camera, the Dart code sends a message through a platform channel to platform-specific code (like Android or iOS), then the native code runs the task (open camera) and sends the result back to Dart.

d. Dart Isolate Setup

Dart Isolate Setup allows Flutter to handle heavy or background operations without blocking the UI by creating isolates. Its purpose is to:

• enable parallel execution in Dart
• ensure safe concurrency with no shared memory
• keep the main UI thread responsive.

e. Rendering

In Flutter, once all widgets are built and arranged by layout and composition, the Engine Layer takes over to draw from the Framework Layer on the screen using a graphics engine called Skia. Now, let us discuss the working of rendering in the Engine Layer.

1. Flutter converts widgets into RenderObjects, carrying the size and layout information
2. A tree of render objects is created
3. Each render paints itself
4. Then, Skia Engine converts this into pixels and sends it to the screen.

f. System Events

System Events are a part of the Flutter Engine that listens to the signals from the native operating system and ensures that your application responds correctly. It acts as a bridge between your Flutter app logic and the host platform’s events, like keyboard inputs, back button press, app lifecycle events, etc. For example, it ensures that your application is properly closed when you press the back button, saves the state of animation when it is paused, and so on.

g. Dart Runtime Management

Dart Runtime Management handles the execution of Dart code, i.e., running, pausing, resuming, and cleaning up Dart programs. It runs the Dart code, handles the Garbage collection, and manages the lifecycle of the Dart program. The main purpose of Dart Runtime Management is to efficiently manage the execution of the Dart code so that the Flutter app stays fast and responsive.

h. Frame Scheduling

Frame Scheduling is a process by which Flutter controls the rendering of the frames on the screen, i.e., it ensures that the app’s UI is updated in sync with the display of the device’s refresh rate in FPS (frames per second), and the visual updates of the UI happen at the right time.

i. Asset Resolution

Asset Resolution is a process of loading the right version of an asset, i.e., images, fonts, and sounds, based on the screen of the device and pixel density. It ensures that your application looks consistent on all devices, from low-resolution to high-resolution.

j. Frame Pipelining

Frame Pipelining is a performance optimization technique that splits the rendering process into multiple stages and processes them in parallel or staggered across frames. This helps Flutter to avoid performance bottlenecks, reduce UI lags, and maintain high frame rates. Without pipelining, each frame will wait for the previous frame to finish processing, leading to delays, but with pipelining, Flutter starts new processes while the last frame is being drawn.

k. Text Layout

Text Layout is responsible for arranging text on the screen, making it look correct and well formatted across all devices and languages. It handles font selection, multilingual rendering, Unicode support (emojis), and so on.

3. Embedder Platform Specific Layer

This is the lowest layer in the Flutter architecture, responsible for embedding the Flutter Engine into each platform, such as Android, macOS, iOS, Windows, or Linux. The other two layers of the Flutter Architecture, Framework Layer and Engine Layer, are shared across the platforms, but the Embedded Layer is platform-specific, i.e., written using native platform languages and APIs. This means:

• It boots up the Flutter engine
• Connect input (touch, keyboard) to Flutter.

Each platform has a different embedder, like,

• Android has Java/Kotlin
• iOS has Swift/Objective-C
• The web has JavaScript
• Windows/macOS/Linux have C++

Now, let us discuss the components present in the Embedder layer.

a. Render Surface Setup

When a Flutter app starts, it first needs a surface (or screen area) to draw its user interface (UI). This process of creating a screen area is called render surface setup. It sets a native window using platform-specific technologies like OpenGL, Metal, Vulkan, and so on, and initializes a native window or canvas on the device, then connects that surface to Skia. It also ensures that everything appearing on Flutter is inside that window.

b. Composition

Composition combines the platform-native window content and Flutter content into one screen. It allows you to add Flutter in one part of the application and combine Flutter with existing native views.

c. Platform Channels

It acts as a bridge between Dart and native code, but from the native side and enabling a two-way communication between Flutter and native APIs. It works as follows:

• Dart code sends a message
• Native code receives that message
• Native code executes the task
• Then, native code sends the result back to Flutter

d. Frame Pipelining

Frame pipelining is how Flutter smoothly shows animations and screens by managing each frame (like the pages in a flipbook) and works with the Flutter engine to schedule and display frames one after another, in sync with the device’s screen refresh rate (called vsync). For example, if a device has a limit of 60fps, the embedder ensures that Flutter does not overproduce frames, i.e., not more than 60 frames per second..

e. Text Layout

It works with the engine’s text layout system to ensure platform-specific font rendering, input handling, and language support. Its working starts when the Flutter engine draws the text, after which the Embedder connects it to the platform’s keyboard, language tools, and accessibility features, so that text works just like it does in native apps.

Why is Flutter a boon for Startups and Companies?

Flutter is a boon for startups because it allows them to build high-quality, cross-platform applications using a single codebase. This means that developers have to write code once, and it will run on Android, iOS, web, and desktop applications. For startups having limited resources, it is a good idea because they can launch their product efficiently, due to its hot reload feature, which increases the development of the application.

Additionally, Flutter uses its rendering engine, Skia, and provides customizable widgets for building consistent UIs. It also supports easy integration with native code, helping companies to use Flutter with existing native code. With strong backing from Google and a growing community, Flutter offers long-term stability and scalability, making it a strategic and cost-effective choice for businesses at any stage.

Get Started with Flutter

Before getting started with Flutter, first, know whether your system is compatible or not.

System Requirements

The following are the system requirements for Windows.

• Operating System: OS should be Windows 10 or Windows 11 (64-bit)
• Disk Space: Disk should be a minimum of 2.5 GB (for Flutter SDK only).
• RAM: RAM should be a minimum of 4 GB.
• Storage Type: SSD is strongly recommended for faster build and emulator speed.

Note: It is recommended to have at least 10 to 15 GB of free storage for SDK, Android Studio/VS Code, emulators, etc.

To get started, install Flutter on your computer, set its path, and configure it with an IDE. Let us understand it in detail.

1. Download Flutter SDK
Go to https://flutter.dev and download the Flutter SDK ZIP file for your operating system.

2. Extract and Set Path
Extract the SDK and add the Flutter bin folder to your system’s environment PATH.

3. Install an IDE

Install the Flutter and Dart plugins from the extensions/plugins marketplace.

Note: It is recommended to use Visual Studio Code or Android Studio.

4. Add Flutter to System PATH

• Open Start, and search “Environment Variables”.

• Edit System Environment Variables, Environment Variables.

• Under System Variables, select Path, Edit, and then New.

• Add path to Flutter’s bin folder

5. Verify Installation
Open a terminal and run:

flutter doctor

This checks your system and shows any missing dependencies (e.g., Android SDK, emulator, etc.).

6. Set Up Emulator or Physical Device
Once your Flutter environment is ready, you need to run your application in a virtual emulator or a real Android phone. Set up an Android Virtual Device (AVD) in Android Studio and then click on the play button.

7. Create a Flutter Project
In the terminal, run:

flutter create my_app
cd my_app

8. Run the App
Launch your emulator or connect your device, then run:

flutter run

Note: Emulators are convenient, but slower and use more RAM

Who Uses Flutter?

Flutter is currently used by startups, enterprises, freelancers, and many global brands to build a cross-platform application. There are many real-world applications of Flutter, and some of the companies using Flutter are:

• Google: The official Google Ads Mobile App is used by Google, having both platforms, ie, Android and iOS. Flutter is developed by Google, hence, they use it to showcase their capabilities. It gives a good look across all the platforms, instant updates and hot reload, and high-performance UI even with heavy data.
• BMW: The My BMW App is a solution for consistent design and a scalable application that BMW needs. It is present in both platforms, i.e., Android and iOS, which have adopted Flutter to reduce duplicate codebases and improve development efficiency.
• eBay Motors: The eBay Motors app required a fast and beautiful application that would enable users to easily buy and sell their vehicles with ease. They used the Flutter camera plugin feature for the vehicle image uploads and used Flutter to build dynamic interfaces without compromising the performance of the app.
• Alibaba: This application has around 50 million active users around the world. In this application, Flutter handled a large amount of data efficiently, created a rich interactive interface, and supported both Android and iOS.

Testing the Flutter Apps

Flutter provides a rich testing framework to help you test your app at multiple levels, from a single function to full UI behavior.

1. Unit Test

Unit Testing in Flutter is a way to test individual functions, methods, or classes in isolation without depending on the Flutter framework, UI, or external systems. The primary goal of Unit Testing is to verify that a piece of code behaves as expected, including edge cases and invalid inputs. Flutter uses the Dart test package for writing and running unit tests. These tests are fast, lightweight, and great for validating business logic, data models, services, or utility functions. It improves code quality, reliability, and easier to maintain. It is the fastest testing technique because it tests a small part of the application and has the smallest scope.

2. Widget Test

Widget Testing, also called component testing in Flutter, is used to test individual widgets and their interactions with the framework, without running a full application. It is between Unit Testing and Integration Testing. The widgets run in simulated environments where the user can interact with them, like tapping, scrolling, entering text, and more. It tests the UI rendering, internal widget behaviour, user interactions like taps, gestures, and navigation inside widgets.

3. Integration Test

Integration Testing in Flutter is used to test the entire application or a large part of an application in a real-world scenario. It ensures that all the widgets, services, navigation, and business logic work together as expected. It tests the flow of the entire application, Widget interactions, Network, API communications, storage, camera, and so on. It is the slowest testing technique because it tests the full application and has the largest scope.

Advantages of Flutter

The following are the advantages of Flutter:

• Single Codebase for All Platforms: Flutter allows you to write one codebase in Dart and run it on Android, iOS, web, and desktop (Windows, macOS, Linux), which saves time and reduces maintenance.
• Hot Reload: Hot reload allows developers to view code changes in real time without restarting the app.
• High Performance: Flutter directly compiles to native ARM code and avoids performance issues, resulting in smooth animations, fast app startup, and good responsiveness.
• Open Source: Flutter is free, open-source, and maintained by Google, with a rapidly growing community and frequent updates, which will give advantage from robust documentation, active development, and access to thousands of packages.
• Customizable UI: Flutter has its own rendering engine (Skia) that draws everything from scratch, giving you full control over every pixel, and enabling the creation of highly custom, animated UIs.

Disadvantages of Flutter

The following are the disadvantages of Flutter:

• Large App Size: Flutter apps have a larger size compared to native apps due to the built-in engine and widget framework, hence it can lead to limited storage.
• Smaller Community Compared to Native Frameworks: Flutter is a newer framework (released in 2017) compared to long-established native development frameworks Java, hence, it is not yet as large or deeply established as the native communities.
• Limited Support for Web and Desktop: Flutter’s support for web and desktop apps is still relatively new and lacks stability or full feature parity and leading to performance issues or limited functionality for non-mobile platforms.
• Dart Language: Flutter uses Dart, which is not as widely known as JavaScript, Java, or Python, due to which developers may face a learning curve, and the smaller ecosystem of Dart can limit support outside Flutter.
• Limited Access to Native APIs: Although Flutter supports many plugins, some advanced or platform-specific features may still require writing native code. This can increase complexity when accessing things like Bluetooth, background tasks, or platform-level security.

Conclusion

From the above article, we concluded that Flutter is an open-source platform helping developers to create one codebase that will run across all platforms, such as web, desktop, iOS, and Android. There are three layers present in its architecture: the Framework layer, the Engine layer, and the Embedder platform layer. Flutter is a boon for many startups and big companies like Google, Alibaba, eBay Motors, and so on. Flutter also supports testing features with Unit testing, Widget testing, and Integration testing, without any external testing tool or IDE required. Apart from this, Flutter has a large app size and limited support for web and desktop applications as compared to Android and iOS applications, hence, it would be used wisely.

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