MVC in App Development: When to Use It and When to Avoid It
Discover How MVC Organizes Your Code and How to Identify Its Limitations
When building an app, it’s tempting to dive straight into coding, focusing on features and getting things done quickly. But without a solid architecture in place, things can spiral out of control. Imagine trying to renovate a house with no blueprint — you might get the job done, but it’ll be messy, hard to maintain, and fixing one part could break another. The same goes for app development.
A well-thought-out architecture helps you keep things organized, maintainable, and scalable. One of the earliest and most popular patterns in iOS and macOS development is MVC — Model-View-Controller.
In this article, we’ll explore the MVC architecture — how it helps keep your code clean and manageable, where it shines, and we will also discuss on why it might not always be the best choice for every project.
What is Architecture in App Development?
Architecture in app development is about how you organize your code and how different parts of the code interact with each other. It’s like giving each part of your app a clear job or responsibility. For example:
One part of the code handles the data (like fetching or storing it).
Another part manages how things look on the screen. This would be the UI part.
And a third part handles the logic, like what happens when a button is tapped.
Good architecture makes sure these parts are separated, so they don’t get tangled up. This makes the app easier to understand, maintain, and update without breaking things.
What is MVC?
MVC (Model-View-Controller) is a design pattern that separates the app into three key components:
Model: Manages data and business logic.
View: Displays the user interface and handles user interactions.
Controller: Acts as a bridge between the Model and View, managing user input and updates.
To handle specific tasks like data fetching, additional layers or services are often used, but they interact with the Controller and Model.
1. Model
The Model is responsible for managing and structuring data. However, it doesn’t fetch data directly from external sources.
Role and Responsibility:
Defines the structure of data (e.g.,
User,Product).Handles business logic, such as validations or simple data transformations.
Stores the state of the app’s data.
Example:
In an e-commerce app, a Product model might have properties like name, price, and description, along with logic to apply discounts.
2. View
The View is responsible for the user interface and presenting data to the user. It listens to user actions but doesn’t perform any logic beyond displaying data.
Role and Responsibility:
Displays data from the Model to the user.
Updates UI elements when the Model changes.
Responds to user actions like button clicks but passes those actions to the Controller.
Example:
In the e-commerce app, the View would show a list of products with images, names, and prices.
3. Controller
The Controller acts as a middleman between the Model and the View. It processes user input and updates the Model or fetches data.
Role and Responsibility:
Handles user input and actions.
Updates the Model when needed.
Tells the View to update based on changes in the data.
Initiates data fetching by calling a service or manager.
Example:
In the e-commerce app, if a user taps a “Refresh” button, the Controller might call a ProductService to fetch new product data, update the Product model, and tell the View to display the updated products.
To help understand how MVC works, let’s consider a simple weather app. The app will display the current weather based on the user’s location. We’ll separate the logic into the View, Model, Controller, and Service layers to see how the communication flows between them.
Let’s break down the code into three main parts:
View: Displays the weather information.
Model: Represents the weather data (e.g., temperature, humidity).
Controller: Manages communication between the View and the Model.
Service: Fetches the weather data from a network API.
Now, let’s take a look at how each component interacts in the MVC architecture.
1. Model
The Model represents the weather data. It holds the properties for weather information and can include any necessary business logic.
// Weather Model
struct Weather {
var temperature: Double
var humidity: Double
var condition: String
}2. View
The View is responsible for displaying the weather data to the user. It only shows information; it does not manipulate it.
// WeatherView (simplified)
class WeatherView {
func displayWeather(weather: Weather) {
// Update UI (labels, icons) to show weather details
print("Temperature: \(weather.temperature)°C")
print("Humidity: \(weather.humidity)%")
print("Condition: \(weather.condition)")
}
}The View shows the current weather and updates whenever the data changes. It receives the data from the Controller and updates the UI accordingly.
In real apps, the View would be tied to actual UI elements (e.g., labels, image views).
3. Controller
The Controller acts as the intermediary. It listens for user actions (e.g., refreshing the weather) and updates the Model. It also updates the View with new data.
// WeatherController
class WeatherController {
var model: Weather?
var view: WeatherView
var weatherService: WeatherService
init(view: WeatherView, service: WeatherService) {
self.view = view
self.weatherService = service
}
func refreshWeather() {
// Request data from the service
weatherService.fetchWeather { [weak self] weather in
self?.model = weather
self?.view.displayWeather(weather: weather)
}
}
}The Controller listens for user actions, like the “Refresh” button press.
It calls the Service to fetch new data and then updates the View.
In this case,
refreshWeather()triggers a network request and updates the View with the new weather data once fetched.
4. Service
The Service is responsible for fetching data from an API or any external source. It doesn’t interact with the View or the Model directly; it only returns the data when requested.
// WeatherService
class WeatherService {
func fetchWeather(completion: @escaping (Weather) -> Void) {
// Simulating a network request to fetch weather data
let mockWeather = Weather(temperature: 25.0, humidity: 80.0, condition: "Sunny")
completion(mockWeather)
}
}The Service is independent of the View and Model. It simply fetches the weather data and passes it back to the Controller.
In a real app, this would involve making actual network requests (e.g., using
URLSessionto fetch weather data from an API).
How the Communication Happens
User Interaction: The user triggers a refresh, like pressing a “Refresh” button.
Controller: The Controller listens for this event and calls the Service to fetch the latest weather data.
Service: The Service fetches the data and passes it back to the Controller.
Model: The Controller updates the Model with the fetched data.
View: The Controller then tells the View to update the UI with the new weather data
Why MVC might not be the go-to architecture for all projects?
As your app grows, the Controller in MVC can become overloaded with logic, especially if it is responsible for multiple views and handling complex interactions. This is often referred to as a “Fat Controller” anti-pattern.
Example:
Imagine you’re building an e-commerce app where the Controller is responsible for managing the cart, checkout process, and user authentication. As more features are added, this Controller can quickly become large and difficult to maintain.
Problem: The Controller starts handling too much business logic, leading to bloated code.
Why MVC Struggles Here: MVC encourages the Controller to handle multiple responsibilities, but this can quickly break the “Single Responsibility Principle.”
Moreover, MVC’s View is tightly coupled with how data is displayed. This makes it challenging when you need more flexible, reusable, and modular UI components.
When MVC doesn’t fit well, there are other architectural patterns that may be better suited to your project needs. We will discuss these in the forthcoming articles.
In Summary: When to Use MVC
Model:
The Model should be used when you are dealing with data and business logic. Ask yourself:
Does the code deal with data storage, validation, or processing?
Is it responsible for interacting with external sources like databases or APIs?
View:
The View is responsible for what the user sees. Use it when you’re working with UI elements that present information. Ask:
Does this code deal with user interface layout and rendering?
Is it focused on displaying data but not manipulating it?
Controller:
The Controller is the intermediary that handles the user’s input and updates the Model and View. It’s useful for:
Does this code coordinate the flow between the View and Model?
Does it respond to user input and update the data or interface accordingly?
When MVC Might Not Fit for Large Projects
For larger, more complex applications, MVC might lead to bloated Controllers, difficult-to-manage Views, and hard-to-scale logic.
To determine if MVC is suitable, ask these questions:
Does the app have complex user flows or multiple dynamic interactions?
Will you need reusable UI components across multiple screens or features?
Is the Controller likely to become too large and difficult to manage as features are added?
Are you planning for scalability, with more features and data integrations as the app grows?
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Exciting stuff 🛐. What is Single Responsibility Principle?