In building mobile apps, reaching the best architecture can help make a project successful. Architectural decisions influence an app’s scalability, maintainability, and long-term success. Proper architecture makes the applications easier to modify functionality, enables parallel development work with fewer conflicts, and prevents the occurrence of refactors. On the other hand, a poor architecture will lead to unnecessarily complex and inefficient code, difficulty in adding features, and a higher chance of bugs or technical debt.
This article will illustrate three of the most commonly used architectural design patterns in modern mobile development: MVC, MVVM, and Clean Architecture. We’ll dive into its major elements, look at the pros and cons, and consider when it’s ideal to use it. Understanding these patterns and their trade-offs will help you decide the best way to proceed with your mobile app so that it’s flexible down the line.
I. Model-View-Controller (MVC)#
MVC is an architectural pattern, and it is one of the oldest, if not the oldest in software development. Many early mobile applications such as early iOS and Android apps adopted MVC due to the very simple separation of concerns with MVC in that it separated the application into its fundamental core roles, which would later cooperate to render the UI and govern user actions in a structured manner.
1. Core Components#
Model: The application’s data and business logic are represented here. The model manages the responsibility of retrieving and storing the app’s data, as well as any rules or calculations related to it. The model serves as the app’s single reliable source of truth for its current state.
View: The user interface. The view displays the app’s data, observes the model or receives data from the controller, and manages anything visualized to the user and the user’s interactions with the app, such as clicking buttons, swiping actions.
Controller: The intermediary between View and Model. The controller responds to the user input that it gets from the view, then updates the model in some way or fetches some data that it gives back to the model, and finally tells the view to update itself in some way.
2. Pros#
Simplicity and Transparency: The structure of MVC is quite simple. It is easy to understand, has three parts, and gives a clear boundary between these parts, making it attractive for beginners.
Framework Support: The initial frameworks for development, such as Apple’s UIKit for iOS, were modeled on the MVC architecture. Hence, such frameworks come with lots of engaged support, built conventions, and documented materials for building MVC apps.
3. Cons#
Massive Controller Risk: When an application scales, the controller classes can carry a risk of leading to code that is overly complex, if not handled properly. This is also called the Massive View Controller problem, which then complicates not only the maintainability of the code but also its testability. A controller, which assumes the bulk of business logic, view updates, and navigation, can thus become a real bottleneck in bigger projects.
Tight Coupling: The view gets very tightly coupled with a controller in MVC, which tends to reduce the degree of flexibility. The heavy dependence on direct manipulation of view elements and responding to UI events makes it difficult to modify the UI or to test the logic of the controller in isolation, makes it hard to reuse the components created, and complicates unit testing.
4. Use Cases#
Small or Simple Apps: The more appropriate use for MVC is in smaller applications, prototypes, or tools where simplicity with only three components outweighs the extensive layering normally required. The simplicity of MVC gives the developer great flexibility in iterating through many development phases with minimal overhead during the early periods of development.
Development Teams with Limited Exposure to Architectural Patterns: If you have little or no knowledge of more complex architectures, starting with MVC is an excellent choice, as it offers a gentle introduction. Concepts are easily grasped, which could very well support delivering a quick functional app, which they could later on refactor.
However, as applications grow more complex, MVC’s limitations become more apparent, like massive controllers and coupling. To address these issues, developers introduced alternative patterns with better separation of concerns, such as MVVM.
II. Model-View-ViewModel (MVVM)#
MVVM is a more modern architecture that really developed to the very full of mitigating some pain points of the MVC. A new component in MVVM is called ViewModel. The major purpose of this component is to further separate the UI from business logic. The ViewModel serves as an intermediate between the View and Model: it holds the data required by the UI, processes it, and updates the View via data binding or observer patterns. Hence, the View has to focus on rendering and can therefore become cleaner while the ViewModel is taking care of anything related to state management and logic. MVVM became increasingly popular in both iOS and Android solutions since it allows for a clean separation and better testability.
1. Core Components#
Model: The data and business logic layer is the same as in MVC. The Model in MVVM is still responsible for fetching, storing, and managing data, like networking requests, database operations, and business rules.
View: The UI layer, which presents information to the user and provides some basic interaction. The View is usually very light and does not include any complex logic.
ViewModel: Mediator of presentation logic. It accepts user events from the View and modifies the Model or performs actions accordingly. Most importantly, the ViewModel does not have a direct reference to UI components, thus decoupling the business logic from the View. In some implementations, the secondary logic for presentation is also handled by the ViewModel, helping to offload such code from the View.
2. Pros#
Separation of Concerns: By decoupling the UI from the business logic, MVVM adopts a cleaner architecture. The ViewModel contains the application’s behavioral logic, making the View simpler. As the project grows, it makes the code more maintainable. UI designers can work on the View while developers focus on the logic in the ViewModel with minimal overlap.
Improved Testability: It’s possible to test the ViewModel using the unit tests when the ViewModel does not depend on the UI framework. In a test suite, instantiate the ViewModel, make mock Model data, and then verify that the correct output or state change occurs. This is much harder to achieve with the tightly coupled view-controller relationship in MVC.
Responsive UIs via Data Binding: MVVM often uses either data binding or reactive programming techniques in order to update the UI automatically in response to changes in the underlying data. When correctly done, applications based on MVVM can provide real-time UI updates with less required support code.
3. Cons#
Increased Complexity: The addition of a ViewModel brings in another level of abstraction as well as project structure. MVVM can be over-engineering for small or simple applications in which the cost for setting up observers and view models is much greater than the possible benefit one could expect from it.
Data Binding Challenges: While extremely powerful, data binding is sometimes difficult to implement and debug. When changes are automatically spread within the binding flow, it becomes hard to follow how the data update occurs in the UI. If not handled accurately, it might also bring memory leaks and degrade performance.
Potential for Massive in ViewModel: If not carefully managed, the ViewModel can be filled with different kinds of logic, just to repeat MVC complexity. Developers should continue to practice proper separation of concerns in the ViewModel in order to eliminate a giant ViewModel that is difficult to maintain.
4. Use Cases#
Medium to Large Applications: MVVM especially excels in medium to high complexity projects with a dynamic application state and frequently changing user interfaces. For example, enterprise mobile applications often include forms, streams of real-time data that could very much benefit from the MVVM structure. The pattern also scales as features are added because new screens can interact with their own ViewModel and Model, uncluttering the unrelated parts of the application.
Apps Requiring Real-Time Updates: Applications that tend to deal with lots of live data, like financial dashboards, social feeds, or IoT dashboards, will benefit from MVVM. Because the observation model will be properly implemented, the UI will automatically and seamlessly update as underlying data changes.
Cross-Platform Development: Since MVVM enables apps to share business logic between different platforms, it allows for both iOS and Android development on the same app. You can share Model code, and even ViewModel code, across multiple platforms with techniques such as the C++ core library or Kotlin Multiplatform, while implementing platform-specific Views.
5. Real-World Example#
A recent fintech project required our team to build a dashboard displaying live financial data. We chose MVVM for that project. The ViewModel handled not just the usual number of data-binding duties, but also a significant number of business-logic tasks. The ViewModel was where we located the Combine framework. Using Combine, we were able to create streams of data that were effortlessly consumed and bound to the View. This approach yielded a highly responsive UI that not just worked, but also allowed the users to see changes in the market immediately without requiring manned refresh intervals.
Even though MVVM solves quite a number of problems associated with MVC and greatly improves code organization, it is not a complete solution. MVVM itself creates additional layers that can become an impediment in very large projects when used incorrectly. To manage the complexity in large-scale systems, developers often turn to Clean Architecture. Clean Architecture uses strict layering to achieve maximum separation of concerns.
III. Clean Architecture#
Promoted by software engineer Robert C. Martin (a.k.a. Uncle Bob), Clean Architecture focuses on a strong separation of concerns and the inversion of dependencies. It means layering the code from business logic, always in a layer, to the details of the framework, user interface, and database. In Clean Architecture, the innermost layers are pure and independent of any external libraries or interfaces, while the outer layers depend upon the inner ones. This ensures that any changes in other parts have little impact on the application’s core business logic.
1. Core Components#
Entities (Domain Layer): Objects that encapsulate the entire domain business and logic. Entities contain important business rules and data structures, irrespective of particular applications and frameworks. For example, in a banking application, we have classes like Account or Transaction with their validation rules, which would reside here.
Use Cases (Application Layer): Sometimes called the Interactor, this layer represents the application-specific operations. Each use case coordinates data flow from and to entities for a specific user action or feature. They embody business rules with entities and are the heart of the application’s behavior. Use cases don’t know about UI or a database; they are simply known programs that could be invoked and tested.
Interface Adapters (Presentation Layer): This layer will transform and present data from the use cases into a form to be consumed by the external layers. Usually, this layer contains Presenters, View Models, or Controllers that will take the raw outputs of the use cases. This layer also contains interface definitions for gateways, so that use cases can interact with external systems through interfaces rather than specific implementations.
Frameworks & Drivers (Infrastructure Layer): This outermost layer is concerned with the real-world implementation details: the UI framework, database, network APIs, device, sensors, or any external interfaces. This layer implements interfaces defined in the Interface Adapter layer. The key point is that these external elements depend not on specific implementations defined in the outer layers but rather on abstract classes defined in the inner layers.
2. Pros#
Highly Maintainable and Scalable: Being a separation of concerns, Clean Architecture makes large code bases easier to understand and modify. Each layer has its own responsibilities and clear boundaries. Such modularity allows a team to work in parallel with minimal conflict. Introducing a new feature simply involves creating new use case classes and modifying the UI, while avoiding clutter in implementation that is not related to that feature.
Testability: Business rules being isolated from each use case class or entity logic can be instantiated without any presence of UI or database. Core logic can be tested in isolation. Integration tests are much easier, as one can intercept external dependencies with mocks implementing the same interface, thus rendering applications more robust and error-proof.
Flexibility and Longevity: Clean Architecture somewhat makes the application future-proof. If you need to change database technology, you can do that with a new adapter implementing the same interface without the need to rewrite business logic. Such adaptability proves to be valuable in an enterprise scenario, where requirements change frequently.
Encourages Good Practices: Clean Architecture principles, such as the dependency rule that states inner classes know nothing about outer classes, encourage developers to think carefully about module boundaries and data flow, and help develop a clean, coherent codebase.
3. Cons#
Initial Complexity: Clean Architecture is highly structured. You’re required to set up all the layers, write data mappers, and define interfaces for everything. And you have to do all of this up front. Development can feel unnecessarily slowed down when following Clean Architecture for what would otherwise be a simple application.
Boilerplate and Overhead: The strict separation from the previous section pretty much mandates that you must write a ton of extra code to pass data around. You have to convert entity objects into data-passing objects that the UI can use. In these cases, you’ll pretty much have to maintain a lot of small classes and interfaces. And if you’re a poor manager, you’re going to have a file explosion.
Requires Strong Discipline: Clean Architecture is not a framework. It’s a guideline. If you want to follow it, you must be disciplined. If any layer starts taking on responsibilities that are outside its scope, most of the advantages of Clean Architecture start going away. Inconsistency or alignment issues can lead to confusion.
4. Use Cases#
Large-Scale Systems and Enterprise Apps: Clean Architecture shines in large applications with complex domains such as fintech, healthcare, and large e-commerce platforms. Enterprise projects requiring extended lifetimes and ongoing maintenance over many years work well with this approach. Its planned refactoring and scaling strategies make the system’s core more stable and reliable.
Multi-Platform Projects & Long-Term Evolution: Substantial functionality added across a well-designed project means that both project and functionality are more stable and likely to be with us for a long time. Such high functionality and project stability make both the overall system and its functionality reliable.
High Reliability and Critical Applications: Uptime or accuracy is a must in a large number of systems. Failure causes bad things to happen, from loss of life in healthcare settings to loss of substance in trading platforms. For these applications, you can’t skimp on testing and validation. Clean Architecture helps you do the necessary testing and validation without getting mixed up in the user interface or messing around with external systems of various kinds.
IV. Conclusion#
Choosing the right architectural pattern for a mobile application depends on the scope, complexity, and long-term goals of the project. Each of the architectures discussed has its place:
MVC: suitable for small applications or prototypes where simplicity and speed of development are important.
MVVM: offers better separation of concerns and testability, suitable for medium to large applications with dynamic user interfaces and growing feature sets.
Clean Architecture: offers the highest level of separation and is advantageous for large-scale, complex applications or those that need to be easily maintained and extended over many years.
It’s important to consider factors like your team’s familiarity with the pattern, the tools and libraries available for your platform, and the expected lifecycle of the application. Sometimes the best solution is a combination, for example, using MVVM at the presentation layer in Clean Architecture, or starting with MVC for a prototype and gradually refactoring parts to MVVM as the project evolves. These patterns are not rigidly exclusive; they are flexible approaches that can be tweaked and even integrated to suit specific needs.
Ultimately, architecture is an investment. It may require more thought and effort up front, but it will pay off by making your application more robust, more testable, and easier to modify as requirements change. By mastering architectural patterns like MVC, MVVM, and Clean Architecture, a software engineer demonstrates systems design capabilities, a critical skill in delivering successful enterprise-scale mobile solutions.
