swift-observation

Swift Observation Framework

The Observation framework provides a robust implementation of the observer design pattern in Swift, introduced in iOS 17, macOS 14, tvOS 17, and watchOS 10 (Swift 5.9+).

Overview

The Observation framework centers around the @Observable macro, which automatically tracks changes to properties and notifies observers. This framework represents a significant improvement over the older ObservableObject protocol, offering better performance and a cleaner API.

Key Benefits

• Fine-grained observation: SwiftUI views only update when observed properties actually change, not when any property on the object changes
• Cleaner code: No need for @Published property wrappers on every property
• Better performance: Views track dependencies at the property level, minimizing unnecessary view updates
• Simpler syntax: Less boilerplate compared to ObservableObject

Using @Observable

To make a type observable, simply apply the @Observable macro to the class declaration:

import Observation

@Observable
class GameState {
    var score: Int = 0
    var level: Int = 1
    var playerName: String = ""

    // Private or computed properties work normally
    private var internalState: String = ""

    var displayName: String {
        "Player: \(playerName)"
    }
}

The @Observable macro automatically:

• Adds conformance to the Observable protocol
• Instruments property accessors to track reads and writes
• Manages observer registration and notification

SwiftUI Integration

Using Observable Objects in Views

With @Observable, you use @State instead of @StateObject:

import SwiftUI

struct GameView: View {
    @State private var game = GameState()

    var body: some View {
        VStack {
            Text("Score: \(game.score)")
            Text("Level: \(game.level)")

            Button("Increase Score") {
                game.score += 10
            }
        }
    }
}

Important: Only the specific properties read in the view's body will trigger updates. If body only reads game.score, changes to game.level won't cause a re-render.