Building a Shared Codebase with Flutter and Dart: A Monorepo Approach

In the modern world of software development, businesses often need to deliver a consistent, high-quality user experience across multiple platforms. A new application might require a mobile version for iOS and Android, a web-based dashboard for administrators, and perhaps a desktop client. This multi-platform reality presents a significant challenge: managing separate codebases for each platform can lead to code duplication, increased maintenance overhead, and an inconsistent user experience.

At Bitswits, a leading mobile app development company in Dallas, we’ve found that the traditional “polyrepo” approach—where each project lives in its own repository—is no longer sufficient for complex, scalable applications. That’s why we’ve embraced a more modern and powerful strategy: the monorepo, powered by the versatile capabilities of Flutter and Dart.

This in-depth guide will explore the monorepo approach for building shared codebases, demonstrating how Flutter and Dart are the perfect tools for the job. We’ll dive into the benefits, provide a practical guide for structuring your project, and offer best practices to help you build highly efficient and maintainable applications.

What is a Monorepo? And Why Does it Matter?

The term “monorepo” is a portmanteau of “mono” (single) and “repository.” It refers to a single, version-controlled repository that contains the code for many different projects, apps, and libraries. This is in stark contrast to the more traditional polyrepo, where each project (e.g., a mobile app, a web app, a backend) has its own separate repository.

On the surface, a monorepo might seem like a simple organizational change, but it unlocks a host of powerful advantages:

• Centralized Code Sharing: With all your code in one place, sharing common models, business logic, and UI components becomes as simple as creating a local package and importing it. This drastically reduces code duplication and ensures a single source of truth for critical logic.
• Atomic Commits: A monorepo allows you to make a change to a shared library and simultaneously update all the applications that depend on it in a single commit. This eliminates the coordination nightmare of managing changes across multiple repositories and ensures that all projects are always compatible with the latest shared code.
• Simplified Dependency Management: With a monorepo, you can standardize the versions of third-party libraries across all your projects. There’s no more risk of one app using flutter_bloc version 8 and another using version 7, which prevents conflicts and simplifies the dependency resolution process.
• Improved Developer Collaboration: A monorepo provides a single, unified view of the entire codebase. This makes it easier for developers to understand how different parts of the system work together and to contribute to different projects, as the entire context is always at their fingertips.

Flutter and Dart: The Perfect Match for a Monorepo

While the monorepo concept can be applied to any technology stack, Flutter and Dart are uniquely suited to this architecture. Their versatility is the key.

Dart, the programming language that powers Flutter, is a “write once, run anywhere” powerhouse. It can be compiled to:

• Native ARM code: For high-performance iOS, Android, and desktop applications.
• JavaScript: For web applications that can run in any modern browser.
• Backend execution: Using a Dart Virtual Machine (VM), it can power backend services, command-line tools, and more.

This cross-platform capability means you can write your core business logic, your data models, and your service layer entirely in Dart within a shared package. Your Flutter mobile app, your Flutter web dashboard, and even a Dart-based backend server can all import and use this single, shared codebase. This is where the magic of the monorepo truly comes to life.

Structuring a Flutter Monorepo: A Practical Guide

A well-structured monorepo is the key to harnessing its power. The most common and effective approach is to separate the codebase into two main directories: packages and apps.

/my_project_monorepo
├── pubspec.yaml (root workspace)
├── packages/
│   ├── models/ (shared data models)
│   │   ├── pubspec.yaml
│   │   └── lib/
│   │       └── ...
│   ├── services/ (shared business logic, e.g., API clients)
│   │   ├── pubspec.yaml
│   │   └── lib/
│   │       └── ...
│   ├── ui_components/ (reusable Flutter widgets)
│   │   ├── pubspec.yaml
│   │   └── lib/
│   │       └── ...
├── apps/
│   ├── mobile_app/ (the main Flutter mobile application)
│   │   ├── pubspec.yaml
│   │   └── lib/
│   │       └── ...
│   ├── web_app/ (the Flutter web dashboard)
│   │   ├── pubspec.yaml
│   │   └── lib/
│   │       └── ...

Here’s a breakdown of the key components:

• pubspec.yaml (Root): A central pubspec.yaml file at the root of the repository defines the workspace and is a recent feature of Dart that makes monorepo management much cleaner. It tells Dart that all packages and apps within the defined paths should be treated as a single workspace. This ensures a single pubspec.lock and a unified dependency resolution for the entire repository.
• /packages: This directory contains all of your reusable, independent Dart packages. These packages can be anything from a simple package for data models to a complex state management or API service layer. The goal is to encapsulate logic in these packages so it can be easily shared.
• /apps: This directory contains your actual applications. Each folder within /apps is a self-contained Flutter project for a specific platform (e.g., iOS/Android, Web, Desktop). These apps will import and use the shared packages from the /packages directory as local dependencies.

Best Practices for Monorepo Development with Flutter and Dart

A monorepo can quickly become unmanageable without a clear set of best practices and tools. Here’s how our expert team at Bitswits approaches it:

1. Package Management with Melos

For large monorepos, manual dependency management and running commands across every package can be a pain. Melos is a powerful command-line tool specifically designed for managing Dart and Flutter monorepos.

• Local Package Linking: Melos’s bootstrap command handles all dependency installation and automatically links local packages together, so you don’t have to use messy path dependencies in your pubspec.yaml files.
• Script Orchestration: You can define scripts in a melos.yaml file to run commands (e.g., flutter test, flutter analyze) across all or a filtered set of packages with a single command.
• Versioning and Publishing: For packages you want to publish to pub.dev, Melos offers automated versioning and changelog generation, simplifying the release process.

2. Architecting for a Shared Codebase

To maximize the benefits of a monorepo, you must architect your code with sharing in mind.

• The Domain-Driven Design: Separate your core business logic and domain models into a dedicated, platform-agnostic package. This package should contain all the rules, validations, and data structures that are central to your application, regardless of whether it’s a mobile app or a web dashboard.
• Abstracting the Service Layer: Instead of putting your API client code directly in each app, create a services package. This package can contain a single HTTP client and all the methods for making API calls. Both your mobile and web apps can then import this package to interact with your backend.
• Shared UI Components: For Flutter apps, you can create a ui_components package to hold your design system. This ensures that every button, text field, and card looks and behaves identically across all your applications, maintaining brand consistency and reducing design debt.

3. Leveraging Code Generation

Code generation is a game-changer in a monorepo. Tools like json_serializable and freezed can be run once to generate boilerplate code for your shared models and services. With Melos, you can easily set up a script to run build_runner across all packages with a single command, ensuring all generated files are up-to-date and consistent.

4. Setting up a Robust CI/CD Pipeline

A monorepo can pose unique challenges for continuous integration and deployment. The key is to use a smart CI/CD tool that understands monorepos. Tools like GitHub Actions, GitLab CI/CD, or Codemagic, when combined with a tool like Melos, can be configured to:

• Only run tests on packages that have changed in a given commit.
• Build and deploy only the applications that were affected by a change in a shared package.
• Automate the versioning and publishing of your shared packages.

This selective execution saves valuable time and resources, making the monorepo approach efficient even for very large codebases.

A Bitswits.co Case Study: Real-World Monorepo Success

Imagine a client approaches us to build a comprehensive service. They need:

• A mobile app for their customers to manage their accounts and access services.
• A web dashboard for their internal team to monitor data and perform administrative tasks.
• A backend to handle business logic, APIs, and database interactions.

Here’s how we would apply the monorepo strategy:

1. We’d create a monorepo with three main apps: mobile_app, web_dashboard, and api_server (a Dart-based backend).
2. We’d create shared packages for the business logic:
   • packages/models: Contains all the data models (e.g., User, Order, Product). We’d use json_serializable here for seamless JSON serialization on both the client and server.
   • packages/services: Contains the ApiClient that both the mobile and web apps use to communicate with the api_server. This ensures all API calls are made with the same logic and headers.
   • packages/design_system: Contains the shared UI components, ensuring a consistent look and feel across the mobile and web interfaces.
3. We would then use Melos to manage the entire repository, running tests and deploying updates with confidence.

This approach would allow our team to work with incredible efficiency. A change to a data model in packages/models could be instantly reflected and tested in both the mobile and web apps, and a change to the API in the api_server could be tested immediately with the api_client in the services package. This dramatically reduces development time and ensures a higher-quality, more consistent final product.

Conclusion: A Modern Approach for a Competitive Market

In a market like Dallas, where businesses are constantly seeking an edge, an efficient and scalable development strategy is a powerful differentiator. The monorepo, combined with the versatility of Flutter and Dart, is a modern solution to the age-old problem of code duplication and cross-platform fragmentation. It’s a strategy that leads to faster development, lower maintenance costs, and a more cohesive, high-quality user experience.

At Bitswits, we are more than just a mobile app development company in Dallas; we are a strategic technology partner. We leverage advanced architectural patterns and modern tooling to build solutions that are not just functional but are also built for long-term success. If you’re ready to build a high-performance, cross-platform application with a shared codebase, contact Bitswits today, and let’s discuss how the monorepo approach can transform your development process.