Lecture 3: MVVM Architecture and Swift Type System

Overview

• Discussed fundamental architecture concepts and type systems in Swift programming.
• Focus on MVVM (Model-View-ViewModel) design paradigm and Swift type system.
• Introduction to building the game logic for the Memorize app.

Key Topics

MVVM Architecture

• Separation of Logic and UI: Essential in Swift to separate app logic/data from UI.
  • Model: Handles logic and data (e.g., card states in Memorize app).
  • View: The UI, or "visual manifestation" of the model.
  • ViewModel: Serves as a "gatekeeper" between the model and view, coordinating interactions.
• Model: Conceptual, not limited to simple structures; could be complex, e.g., databases or APIs.
• UI: Parameterizable shell; merely displays model information.

Connecting UI and Model

• Strategy 1: Model as @State in view - minimal separation.
• Strategy 2: Model accessible via ViewModel - main approach in MVVM.
• Strategy 3: Hybrid - ViewModel allows some direct access to the model.

Model-View-ViewModel (MVVM)

• ViewModel: Interprets and binds the model to the view; ensures UI reflects model changes.
• Data Flow: Changes in model detected by ViewModel, which signals updates to UI.
• User Intent: Processed by ViewModel, modifying the model based on user actions.

Type System in Swift

• Structs and Classes
  • Structs: Value types, copied on assignment.
  • Classes: Reference types, share pointers.
  • Use structs primarily in Swift due to functional programming style.

Differences

• Value vs Reference Types: Structs are copied, classes are referenced.
• Mutability: Explicit in structs; classes always mutable.
• Inheritance: Exists in classes, not in structs.

Generics

• Type Agnosticism: Enable functions and structs to operate on any data type.
• Syntax Example: struct Array<Element>, where Element is a generic placeholder.
• Application in MVVM: Memorize game using generic types for card content.

Protocols

• Definition: Describes a set of methods and properties without implementations.
• Usage: Define behavior a type conforms to; can also use for type constraints.

Protocols in Swift

• Protocols as types: Used as parameters or variables.
• Constrains and Gains: Protocols constrain types to gain functionalities like methods.

Functions as Types

• First-Class Functions: Functions are a primary type, can be passed around in code.
• Closure: Inline functions capturing the surrounding context.

Demo Overview

• Began structuring the Memorize app model separate from UI.
• File Setup: Created new Swift files for model and view model.
• Implementation: Defined MemoryGame struct with nested Card struct.
• ViewModel: Introduced EmojiMemoryGame class to manage model-view interaction.

Conclusion

• Covered MVVM architecture, emphasizing model-view separation, and Swift type systems.
• Prepared foundation for further UI development using MVVM principles.