JKOAssignment

App architecture

Note: Please refer to the App architecture diagram.drawio file if you would like to have a clear sight of the diagram. Drag and drop the file on the website of the Draw.io.

Design decision

• Implemented modular system by respecting S.O.L.I.D. principle to create Item, Order, CoreData and Shared layer and composing them in Composition layer. There are sublayers in the Item and Order, including Feature (business logic), Local, UI and Stub. With such clear separation, they can be separated into different modules if needed.

Item layer

• Includes 商品列表 (includes pagination), 商品詳情 and 購物車 scenes.

Order layer

• Includes 確認訂單 and 歷史訂單紀錄 (includes pagination) scenes.

CoreData layer

• Acted as an adapter between CoreData framework and Local sublayer of Item and Order by implementing Local-specific abstraction.

Shared layer

• Shared UI components and helpers between Item and Order.

Composite layer

• Acted as all layers' client to initialize all components this application needs.
• Also decorated components differently based on the requirements.

Feature sublayer (Business logic)

• Defined feature abstraction components instead of concrete types. This way, the system can be more flexible when facing requirements changes by creating different implementations of the abstraction and composing them differently without altering the existed components.
• Also, other sublayers are able to be developed in parallel by following the defined abstraction.

UI sublayer (Includes Presentation layer)

• Implemented MVVM as UI architecture to separate iOS-specific components (import UIKit) from feature logic (platform-agnostic) by using platform-agnostic presentation components (ViewModel). This way, the ViewModel can be reused across platforms if needed.
• Used closure as binding strategy to achieve simplest way of binding.
• Implemented multiple MVVMs in one scene to avoid components holding too many responsibilities (massive view controller).
• Used Composer to reduce the complexity of creating a scene with multiple MVVMs from clients point of view.
• Decoupled UIViewControllers by using closure callback to send UIViewController navigation events to its client intead of creating another UIViewController within an UIViewController.

Local sublayer

• Hid the frameworks' details by depending on a local-specific abstraction (invert the dependency). This way, I can easily switch the frameworks based on the needs without altering current system.
• Separated the frameworks' details from business logic also make the framework components easy to test, develop and maintain since it just obeys the command.
• Created local-specific models to decouple CoreData sublayer from Feature sublayer and other components in Local sublayer.

Stub sublayer

• Only for this assignment-specific case. Normally it would be a API sublayer and applied the same concept in the Local sublayer.

Design pattern

Decorator

• Dispatched the UI-specific results from background queue to main queue by MainThreadDispatchDecorator to eliminate duplicate code in UI layer.
• Decoupled Order from Item layer by using OrderSaverWithCartDeleterDecorator for cart deletion after completing the checkout process.

Adapter

• Decoupled Local sublayer from CoreData by using CoreDataStore.

Null Object

• Instead of making the application crash when the creation of CoreData stack failed, used NullStore to provide empty implementation.

Requirements

Xcode 13 or later
iOS 15.0 or later
Swift 5 or later

Contact

Wayne Cheng｜h88377@gmail.com

Licence

JKOAssignment is released under the MIT license.