Android Multi Module Concept

Building an Android app with a multi-module approach is a great way to improve code organization, build times, and team collaboration. When deciding on the granularity of your modules, there are trade-offs to consider for both approaches:

1. Small, Single-Page Modules (List, Detail, Profile)

Pros:

• Increased Isolation and Decoupling: Changes in one small module are less likely to affect other parts of the app. This reduces the risk of unintended side effects and makes refactoring easier.
• Faster Build Times (Potentially): Smaller modules generally compile faster, especially for incremental builds when only a small part of the app has changed.
• Improved Parallel Development: Different developers or teams can work on different features (modules) with less risk of merge conflicts.
• Better Code Reusability (Potentially): If a single page or a small set of UI elements is highly reusable across different parts of the app, a dedicated module can facilitate this.
• Clearer Feature Boundaries: The app's features are clearly separated at the module level, making it easier to understand the application's structure.
• Easier Testing: Individual modules can be tested in isolation, leading to more focused and efficient unit and integration tests.
• Dynamic Feature Delivery Potential: If you intend to use Dynamic Feature Modules in the future, this granular approach aligns well with delivering features on demand.

Cons:

• Increased Project Complexity: A large number of modules can make the project structure seem more complex to navigate initially.
• More Overhead: Each module adds some overhead in terms of Gradle configuration and potential boilerplate code for communication between modules.
• Potential for Increased Inter-Module Communication: If many small modules need to interact frequently, you might end up with more complex communication mechanisms.
• Higher Initial Setup Effort: Creating and configuring a large number of modules can take more time at the beginning of the project.
• Potential for Redundancy: You might end up with similar dependencies or utility classes duplicated across multiple small modules if not managed carefully.

2. Larger, Multi-Page Modules (Wallet, Flight, Hotel)

Pros:

• Reduced Project Complexity (Visually): A smaller number of modules can make the project structure appear simpler and easier to grasp at a high level.
• Simplified Dependency Management: Fewer modules mean fewer build.gradle files to manage and potentially fewer duplicate dependencies.
• Easier Feature Grouping: Logically related features and their associated screens are grouped together, which can make it easier to understand the scope of a particular feature.
• Potentially Simpler Navigation: Navigation within a larger module might be perceived as simpler as the related screens are contained within the same scope.
• Lower Initial Setup Effort: Creating a smaller number of larger modules is quicker initially.

Cons:

• Increased Coupling: Changes in one part of a large module can potentially affect other seemingly unrelated parts within the same module.
• Slower Build Times (Potentially): Larger modules take longer to compile, increasing overall build times, especially for incremental builds.
• Increased Risk of Merge Conflicts: When multiple developers work on the same large module, the chances of merge conflicts in the code and resources are higher.
• Reduced Isolation: It becomes harder to isolate and test specific parts of a feature when they are tightly coupled within a large module.
• Limited Code Reusability (Potentially): UI elements or logic within a large module might be harder to reuse in completely different parts of the application.
• Less Alignment with Dynamic Feature Delivery: It's less straightforward to deliver parts of a large module on demand using Dynamic Feature Modules.

Which one is better depends on your specific project requirements, team size, and long-term goals.

General Recommendations:

• Start with a modular approach from the beginning. It's much harder to refactor a monolithic codebase into a modular one later.
• Consider the logical boundaries of your features. Group screens and functionalities that are tightly related into a single module.
• Aim for a balance. Creating an excessive number of very small modules can lead to unnecessary complexity. Similarly, having very large modules can negate the benefits of modularization.
• Think about potential reuse. If a set of UI components or functionalities is likely to be used in multiple distinct features, consider placing them in a separate, smaller module (e.g., a ui-components or utils module).
• Consider your team structure. If you have multiple small teams focusing on specific features, smaller, well-defined modules can improve collaboration.
• Plan for inter-module communication. Decide how different modules will interact (e.g., using interfaces, dependency injection, or navigation components).
• Keep build times in mind. Regularly monitor your build times as your project grows. If build times become a significant issue, you might need to re-evaluate your module structure.
• Don't be afraid to refactor. As your app evolves, you might need to adjust your module boundaries.

In summary:

While creating very small, single-page modules offers the highest degree of isolation and potential for faster incremental builds, it can also lead to increased project complexity and overhead. Creating larger, multi-page modules simplifies the initial project structure but can lead to increased coupling and slower build times.

A good strategy is often to lean towards creating modules based on logical features or significant flows within your application (like "wallet," "flight booking," "user profile"), even if they contain multiple screens. Within these larger feature modules, you can still strive for internal separation of concerns and create smaller, reusable components.

Think of it as finding the right level of granularity that balances isolation, build performance, maintainability, and team collaboration for your specific context. You might even end up with a mix of both approaches, where core features are in larger modules, and highly reusable components or isolated functionalities reside in smaller modules.

Let's break down what typically resides within the core, data, feature, and app modules in this context:

1. core Module:

The core module acts as the foundation of your application. It contains fundamental components and functionalities that are used across multiple other modules. It should be highly stable and have minimal dependencies on specific features.

Typical contents of the core module:

• Base Classes:
  • Base Activity/Fragment classes that provide common functionality (e.g., view binding setup, error handling).
  • Base ViewModel classes with common logic (e.g., handling loading states, common data transformations).
  • Base Use Case/Interactor interfaces and potentially abstract implementations.
  • Base Repository interfaces.
• Dependency Injection (DI) Setup:
  • Core DI modules (e.g., providing application context, basic networking configurations). You might use libraries like Hilt or Dagger.
  • Potentially some application-scoped bindings.
• Common Utilities:
  • Helper functions and utility classes (e.g., date/time formatting, string manipulation, network checking).
  • Constants used across the application.
  • Extension functions on common Android classes (Context, View, etc.).
• Threading/Concurrency Management:
  • Abstractions or wrappers around threading mechanisms (e.g., Coroutine Dispatchers).
• Navigation Abstraction (Optional):
  • Interfaces or abstract classes for navigation if you want to decouple feature modules from a specific navigation implementation.
• Common UI Components (Potentially):
  • Small, highly reusable UI components (e.g., custom buttons, text fields) that are used across many features. However, be cautious not to make this module too UI-centric.

Key Characteristics of core:

• Low Coupling: Should have minimal to no direct dependencies on feature modules.
• High Cohesion: Contains logically related, fundamental functionalities.
• Stability: Changes in core should be infrequent and carefully managed as they can impact the entire application.

2. data Modules (data:user, data:wallet, data:flight, data:hotel):

These modules are responsible for handling the data layer for specific domains. They abstract away the data sources (local database, network APIs, etc.) and provide a clean API for the feature modules to access data.

Typical contents of a data module (e.g., data:user):

• Data Sources:
  • Implementations for local data sources (e.g., Room DAOs, SharedPreferences).
  • Implementations for remote data sources (e.g., Retrofit API service interfaces and implementations).
• Repositories:
  • Implementations of the repository interfaces defined in the core or potentially within the data module itself. Repositories mediate between data sources and provide a single point of access to data for the feature modules.
  • Logic for caching, data transformation, and selecting the appropriate data source.
• Data Transfer Objects (DTOs) / Network Models:
  • Classes representing the data structures received from network APIs.
• Entity/Database Models:
  • Classes representing the data structures stored in the local database.
• Mappers:
  • Functions or classes responsible for mapping between DTOs, entities, and domain models (which might reside in the feature module or a separate domain layer if you have one).
• Dependency Injection (DI):
  • DI modules specific to the data layer (e.g., providing Room database instances, Retrofit services).

Key Characteristics of data Modules:

• Responsibility: Focused on data retrieval, persistence, and manipulation for a specific domain.
• Abstraction: Hides the details of data sources from the feature modules.
• Independent: Each data module should ideally be independent of other data modules, except for potential shared data models or core utilities.

3. feature Modules (feat:user, feat:wallet, feat:flight, feat:hotel):

These modules contain the specific user-facing features of your application. They depend on the core and relevant data modules to implement their functionality. Each feature module typically contains the UI (Activities, Fragments, Composables), ViewModels, and Use Cases/Interactors related to that specific feature.

Typical contents of a feature module (e.g., feat:user):

• UI Components:
  • Activities, Fragments, Composables that make up the user interface for the user-related screens (e.g., profile screen, login screen, registration screen).
  • Layout files (XML or Compose).
  • UI-specific ViewHolders, Adapters, and custom views.
• ViewModels:
  • Classes responsible for preparing and managing data for the UI, handling user input, and interacting with Use Cases.
• Use Cases/Interactors:
  • Classes that encapsulate specific business logic for the feature. They typically interact with the repositories in the data modules and provide data to the ViewModels in a UI-agnostic way.
• Navigation Logic (Within the Module):
  • Code related to navigating between screens within the user feature.
• Dependency Injection (DI):
  • DI modules specific to the feature module (e.g., providing ViewModels, Use Case instances).
• Local Data/State Management (Feature-Specific):
  • Any local data or state management specific to the UI of this feature.

Key Characteristics of feature Modules:

• Business Logic: Contains the specific logic and workflows for a particular feature.
• UI Presentation: Responsible for displaying information to the user and handling user interactions.
• Dependency: Depends on core and the relevant data modules. Should ideally not have direct dependencies on other feature modules to maintain isolation.

4. app Module (app:ota):

The app module is the entry point of your Android application. It's responsible for assembling all the other modules and providing the necessary glue code to make the application run.

Typical contents of the app module:

• Application Class:
  • The main Application class for your app, responsible for initialization.
• Navigation Graph:
  • Defines the overall navigation flow between different features (often using the Android Navigation Component). This is where you connect the entry points of different feature modules.
• Dependency Injection Setup (Application-Wide):
  • The root DI component that orchestrates the creation and injection of dependencies across all modules.
• Manifest File:
  • The AndroidManifest.xml file that declares the application's components, permissions, and other essential information.
• Gradle Configuration (Application Level):
  • The build.gradle file for the app module, which includes dependencies on all the core and feature modules.
• Potentially Initial Activity:
  • The main launcher Activity of your application.

Key Characteristics of app:

• Orchestration: Responsible for bringing all the modules together.
• Thin Codebase: Ideally, the app module should contain minimal business logic and UI code. Its primary role is composition.
• Dependency: Depends on all the core and feature modules.

Benefits of this Modular Structure (Revisited with Context):

• Clear Separation: Each feature (feat:user, feat:wallet, etc.) is isolated. Changes in the "wallet" feature are unlikely to cause unexpected behavior in the "user profile" feature.
• Faster Build Times: When you modify code within a specific feature module, only that module and its direct dependencies need to be rebuilt, significantly reducing build times compared to a monolithic app.
• Improved Parallel Development: Different teams or developers can work on different feature modules concurrently with less risk of conflicts.
• Better Code Organization and Maintainability: The codebase is well-structured and easier to navigate, understand, and maintain.
• Increased Code Reusability: The core module provides common functionalities that can be reused across all features.
• Easier Testing: Individual feature modules can be tested in isolation, leading to more focused and reliable tests.
• Potential for Dynamic Feature Delivery: This structure makes it easier to adopt Dynamic Feature Modules in the future, allowing you to deliver certain features on demand.

By adopting this multi-module architecture, you can build a more scalable, maintainable, and efficient Android application. Remember to carefully define the boundaries of your modules based on logical features and strive for clear dependencies between them.

data:user & data:wallet will use on feat:hotel

Is it correct?

Yes, it is absolutely correct and a common scenario in a well-modularized Android application. Here's why and how this would work:

Reasoning:

• Feature Dependencies: The feat:hotel module likely needs information related to both the user and their wallet for certain functionalities. For example:

  • User Information: To personalize the hotel booking experience (e.g., displaying the user's name, pre-filled details).
  • Wallet/Payment: To allow the user to pay for their hotel booking using their stored payment methods or view their loyalty points/balance.

• Layered Architecture: The feature modules should depend on the data modules to access and manipulate data. They should not directly interact with data sources (like network APIs or databases). This separation of concerns is a key benefit of modularization.

How it Works:

1. feat:hotel Dependency: The build.gradle file of the feat:hotel module will include dependencies on both data:user and data:wallet.

   // In feat:hotel/build.gradle

   dependencies {
       implementation project(':core') // Assuming core has common interfaces
       implementation project(':data:user')
       implementation project(':data:wallet')
       // ... other dependencies
   }
   

2. Repository Interaction: Within the feat:hotel module (likely in its ViewModels or Use Cases), it will interact with the repositories exposed by the data:user and data:wallet modules.

   • data:user Repository: The feat:hotel module might use the UserRepository (provided by data:user) to fetch user details.
   • data:wallet Repository: The feat:hotel module might use the WalletRepository (provided by data:wallet) to retrieve payment methods or initiate payment processes.

3. Abstraction: The feat:hotel module doesn't need to know the underlying implementation details of how user or wallet data is fetched or stored. It only interacts with the clean, abstract interfaces provided by the repositories in the data modules.

Benefits of This Approach:

• Reusability: The data:user and data:wallet modules can be reused by other feature modules (e.g., feat:flight might also need user information and wallet functionality).
• Maintainability: Changes to how user or wallet data is handled are isolated within their respective data modules and won't directly impact the feat:hotel module (as long as the repository interfaces remain consistent).
• Testability: The feat:hotel module can be tested in isolation by mocking or faking the UserRepository and WalletRepository.
• Clear Dependencies: The dependencies between modules are clearly defined in the build.gradle files, making the application's structure easier to understand.

In summary, it's a good and expected practice for feature modules to depend on multiple relevant data modules to access the necessary data for their functionality. This promotes a well-organized, decoupled, and maintainable codebase.