Flutter Architecture

The architecture of a Flutter app is built on a layered system, which ensures smooth performance, fast rendering, and a well-organized structure for development. Each layer in Flutter plays a specific role, working together to deliver a seamless user experience across platforms like Android, iOS, web, and desktop.

1. Flutter Architecture Overview

Flutter follows a three-layer architecture, which includes:

1. Embedder (Platform-specific integration)
2. Engine (Core Rendering and Platform Services)
3. Framework (UI design, state management, business logic — written in Dart)

2. Layers of Flutter Architecture

a. Embedder Layer

Role:

• This is the platform-specific layer that connects Flutter to the native environment — whether it’s Android, iOS, web, or desktop.
• zzProvides communication channels between Dart and native native components.
• Manages app lifecycle, input events, and rendering surfaces.

Examples:

• On Android: On Android: Kotlin/Java code in MainActivity.kt or MainActivity.java.
• On iOS: Swift/Objective-C code in AppDelegate.swift or AppDelegate.m.
• Why it matters: Without this layer, your Flutter code wouldn’t know how to run on different platforms.

b. Engine Layer

Role: This is the core engine of Flutter, written in C++, responsible for rendering graphics, handling inputs, and managing communication between Dart and the native platform.

• Rendering the UI using Skia, a fast 2D graphics engine.
• Managing text layout, animations, and compositing.
• Handling I/O events (touch, keyboard, mouse).
• Running the Dart virtual machine for executing code.
• Using platform channels to call native features (e.g., camera, GPS).

Key Components:

• Dart Runtime → Executes Dart code .
• Skia → Draws everything on the screen.
• Platform channels: Bridges native code and Dart for features like camera, GPS, etc.

c. Framework Layer

Role:This is the part that developers interact with the most. Written entirely in Dart, the framework layer contains the tools and libraries used to build the app’s user interface, handle user input, manage app state, and more. It provide:

• Predefined widgets (StatelessWidget, StatefulWidget, etc.).
• Tools for navigation, animations, layout and gesture handling.
• Libraries for building responsive, interactive UIs.

Key Components:

• Widgets → The UI elements you use to build your app (buttons, texts, layouts).
• Rendering Layer → Handles layout and painting of widgets.
• Foundation Library → Offers basic utility classes and APIs (like async, math, List, etc.).

3. Flutter Application Structure

Entry Point

The app starts from main() in Dart.

void main() {
  runApp(MyApp());
}

4. Example: Flutter Architecture in Action

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(primarySwatch: Colors.blue),
      home: MyHomePage(),
    );
  }
}
    

5. Key Advantages of Flutter’s Architecture

Flutter’s layered and component-based architecture brings several powerful advantages that make it a popular choice among developers:

• Hot Reload: One of Flutter’s most loved features — Hot Reload allows developers to see changes in the code instantly, without restarting the app. Whether you're tweaking UI design or fixing logic, the feedback is immediate, speeding up development.
• Customizable UI: Flutter uses a declarative UI model built entirely with widgets. This gives you full control over every pixel on the screen, making it easy to design highly customized and beautiful interfaces.
• Cross-Platform Development: With Flutter, you can write a single codebase and run it on Android, iOS, Web, Desktop, and even embedded devices. This saves both time and resources while maintaining consistency across platforms.
• High Performance: Flutter uses Skia, a powerful 2D rendering engine, to render everything on the screen. It ensures smooth animations, fast UI rendering, and excellent performance even on older devices.

Widgets

The most important idea in Flutter is that everything is a widget. Widgets are the building blocks of a Flutter app’s user interface. Whether it's a simple text, a button, or the entire screen layout – it’s all made using widgets. In Flutter, even the whole application itself is a widget. This top-level widget contains other widgets as its children, and those children can also have their own child widgets. This nested, tree-like structure makes it easy to build complex user interfaces by combining simple components. This concept of composability – building UIs by combining smaller widgets – allows developers to create beautiful and functional apps, no matter how simple or complex the design is.

Everything in Flutter is a widget, which is either:

• StatelessWidget: These widgets are immutable, meaning they don’t change during the app’s runtime.
• Ideal for UI elements that remain constant.
• Example: Static texts, icons, images.
• StatefulWidget: These widgets are mutable and can hold dynamic data or state.Useful for interactive components like forms, counters, or anything that updates based on user actions.

MyApp
(Top level / Root)

MaterialApp

MyHomePage
(Property: home)

Scaffold

AppBar
(Property: appBar)

Center
(Property: body)

Text
(Property: child)

• MyApp This is a user-created widget.It uses the native Flutter widget: MaterialApp, which sets up the app’s structure and theme.
• MaterialApp Has a property called home, where you define the main screen of the app.This is usually set to another user-created widget, like MyHomePage.
• MyHomePageInside this widget, we use Scaffold, a Flutter native widget that provides a basic layout structure.
• Scaffold Has two main properties:appBar: Defines the top/header area. body: Defines the main content area.
• AppBar This widget is used to create the app’s title bar or header.
• Center In the body, we often use the Center widget to align content to the center of the screen.
• Text Inside the Center, we use a child property to display actual content — such as the Text widget to show text on the screen.

Layers

One of the key concepts behind the Flutter framework is its layered architecture, which organizes the framework into different categories based on complexity. These layers are neatly arranged in a hierarchy, with each one built on top of the layer below it. At the top of the stack, you’ll find widgets that are specific to platforms like Android and iOS. Just below that are the core Flutter widgets — these are the standard UI building blocks like buttons, text, and layout elements. Next comes the Rendering Layer, which handles all the low-level drawing and layout tasks. This layer is responsible for actually painting everything you see on the screen. Beneath this lies the foundation of Flutter — the platform-specific code that interacts directly with the native operating system.

The general overview of a layer in Flutter is specified in the below diagram:

Platform Specific Widgets

Widgets

Rendering

Animation / Painting / Gestures

Foundation

C / C++ Engine

Platform Specific

The following points summarize the architecture of Flutter:

• In Flutter, everything is a widget — even layout structures and design elements. Complex UIs are built by combining simpler widgets.
• You can add interactivity (like tap, swipe, and drag) using the GestureDetector widget.
• If you need to keep track of changing data or UI, you can use a StatefulWidget to manage the widget’s state.
• Flutter offers layered design so that any layer can be programmed depending on the complexity of the task.