Structural Patterns

Last Updated: Dec 7, 2024

Structural patterns help organize and manage relationships between objects to form larger structures and enhance flexibility and reusability.

WARNING

I am only listing the ones that I've been dealing with or interact with a couple of times 😃

TL;DR

• Adapter: Makes incompatible interfaces compatible by acting as a translator.
• Bridge: Separates an abstraction from its implementation, letting both vary independently.
• Decorator: Adds extra features to an object dynamically, like layers on top of the base.
• Model-View-Controller: Separates data, interface, and control logic for organized structure.
• Model-View-ViewModel: Enhances MVC by adding a ViewModel, which acts as a bridge between Model and View, allowing data binding and cleaner separation of business logic and UI.

Adapter Pattern

Definition

The Adapter Pattern helps two pieces of code with different interfqces work together. It’s commonly used when integrating third-party libraries or legacy code that doesn't match the expected interface.

Think about when you are traveling: when you decide to travel to a different continent, it's complicated to use a power outlet! That's where the plug adapter comes in, and helps you to adapt your charger. Same here!

Flow

• Adapter Creation: The adapter class is created, implementing the interface and methods expected by the client.
• Adaptation: The adapter translates or maps requests from the client interface to the adaptee's interface.
• Usage: The client can now use the adapter as if it were using the original system or class.

-> So, an adapter class sits between two incompatible parts, takes requests from one part, translates it, and sends it to the other part, so it can understand.

Bridge Pattern

Definition

The Birdge Pattern helps split an abstraction (a high-level idea) from its implementation (the details). Need an example? I got one for you: suppose you have a magic remote that controls a devices such as different TVs. Well, the abstraction is the remote, and the remote is used by implementations such as the TVs.

INFO

The relation Has-A defines the bridge between the two hierarchies (Remote and TV)

Flow

• Abstraction: Defines a high-level interface, often extendeed by refined abstractions.
• Implementation: Concrete implementations are separated into their own classes.
• Usage: The abstraction delegates operations to the implementation, allowing both to evolve independetly.

-> We got two parts: one for general controle (the remote), and one for the specific device (the TV, the Radio). The remote sends signals, but each device responds its way.

Decorator Pattern

Definition

The Decorator Pattern lets you add new features or "decorations" to an object ithout changing its structure. It's like adding extra toppings on a pizza–the pizza stays the same, but you add things to it!

Flow

• Component Interface: Defines the base interface for objects that can have responsibilities added.
• Concrete Component: The object being decorated.
• Decorator: Wraps the component, adding new behavior while conforming to the same interface.
• Usage: Multiple decorators can be stacked to add layered behaviors dynamically.

-> You have a basic object (like a plain pizza), and then you can wrap it with decorators (extra cheese, pepperoni) that add extra functionality or features. Each decorator adds something new.

Model-View-Controller (MVC)

Definition

The MVC is a fundamental design pattern in iOS development. It seperates the data (Model), user interface (View), and the logic that connects them (Controller).

• The Model represents the data and business logic of the application. It is responsible for retrieveing data, managing it, and notifying the View when data changes.
• The View displays the user interface and presents the data to the user.It listens for user input and forwards these actions to the Controller.
• The Controller acts as am intermediary between the Model and the View. Receives input from the View, processes it (often involving calls to the Model), and upadtes the View accordingly.

Flow

• The View receives user input (1) and notifies the Controller (1🔔).
• The Controller interacts with the Model to get or update data (2).
• Once the Model is updated of fetched (🔄3), the Controller updates the View (3).

Model-View-ViewModel (MVVM)

Definition

The MVVM enhances the MVC pattern with a ViewModel layer that separates business logic from the View.

• The Model is similar to MVC, which represents the data and business logic of the application.
• The View displays the user interface and binds to properties exposed by the ViewModel.
• The ViewModel acts as an intermediary between the Model and the View, and exposes data in a way that the View can easily consume. It provides properties that the View can bind to, and it may include methods that the View can invoke without needing to know the specifics of the Model.

Flow

• The View binds to properties in the ViewModel (1).
• When the ViewModel receives updates from the Model or processes user input, it notifies the View of changes (2).
• The View updates automatically based on the data bound to the ViewModel (3).