Journey to Clean Architecture: Wrestling with a 10k Line Flutter Legacy Codebase

The Challenge

I'm currently undertaking an ambitious project: migrating a 10,000-line Flutter application to Clean Architecture. This first post in a series documents the challenges I've encountered, with solutions coming in the follow-up post.

Core Issues

The primary challenge stems from violated Separation of Concerns principles. The codebase has become a tangled web where business logic, backend calls, and UI code coexist within the same files. To make matters worse, singletons appear frequently (I'll address why this is problematic in a dedicated post).

Before: The Problematic Code

// A typical example of violating Clean Architecture principles
class HomeScreen extends StatefulWidget {
  @override
  _HomeScreenState createState() => _HomeScreenState();
}

class _HomeScreenState extends State<HomeScreen> {
  // ❌ UI State mixed with business logic
  List<Product> products = [];
  bool isLoading = false;
  String error = '';

  // ❌ Direct API calls in widget
  void fetchProducts() async {
    setState(() => isLoading = true);
    try {
      final response = await http.get('api/products');
      // ❌ Business logic mixed with data fetching
      final parsedProducts = parseProducts(response);
      // ❌ Direct state manipulation
      setState(() {
        products = parsedProducts;
        isLoading = false;
      });
    } catch (e) {
      // ❌ Error handling mixed with UI
      setState(() {
        error = e.toString();
        isLoading = false;
      });
    }
  }

  // ❌ Business logic in UI layer
  List<Product> parseProducts(Response response) {
    final data = json.decode(response.body);
    return data.map((json) => Product.fromJson(json)).toList();
  }

  @override
  Widget build(BuildContext context) {
    // ❌ Complex UI with business logic
    return Scaffold(
      body: isLoading 
          ? CircularProgressIndicator()
          : error.isNotEmpty
              ? Text(error)
              : ListView.builder(
                  itemCount: products.length,
                  itemBuilder: (context, index) {
                    // ❌ Business logic in view
                    final discountedPrice = 
                        calculateDiscount(products[index].price);
                    return ProductCard(
                      product: products[index],
                      discountedPrice: discountedPrice,
                    );
                  },
            ),
      );
  }
}

Key Challenges Encountered

1. Architectural Ambiguity

• Business logic scattered across widgets without clear boundaries
• No defined data flow patterns or architectural guidelines
• Mixed responsibilities making code hard to understand and maintain

2. State Management Chaos

• Multiple competing state management approaches
• Overuse of global state through singletons
• Unclear state ownership and update patterns

3. Testing Nightmare

• High coupling making unit tests nearly impossible
• Brittle UI tests breaking with business logic changes
• No clear mocking boundaries for testing

4. Structural Issues

• Inconsistent project structure
• Unclear module boundaries and dependencies
• No separation between layers

5. Error Handling Inconsistencies

• Different error handling patterns across the app
• Missing unified error recovery strategy
• Poor user feedback mechanisms

6. Performance Problems

• Excessive widget rebuilds due to poor state management
• Bloated widgets handling multiple concerns
• Unnecessary computations in build methods

7. Maintenance Hurdles

• High risk when adding new features
• Bug fixes often causing regression issues
• Technical debt slowing down development

8. Documentation Gaps

• Missing architectural documentation
• Unclear component dependencies
• No clear guidelines for new code

What's Next?

Stay tuned for my next post where I'll share practical solutions to these challenges, including:

• Implementing Clean Architecture layers
• Setting up proper dependency injection
• Establishing clear state management patterns
• Creating comprehensive testing strategies

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Share your experiences with similar challenges in the comments below! Have you successfully migrated a large Flutter codebase to Clean Architecture? What obstacles did you face?

Flutter #CleanArchitecture #CodeRefactoring #SoftwareEngineering