Observation Back-Porting

Proof of Concept for back-porting Observation framework to earlier iOS versions.

The same APIs as the Observation framework are provided but without the limitation of iOS 17.

Verified on Xcode 15.0 beta 5 (15A5209g). May break with a future version of Xcode.

Just a toy and only for PoC. Do not use it in your production code (or at your own risk)!

Usage

Macro

Just as the official Observation framework, but importing ObservationBP:

import ObservationBP

@Observable fileprivate class Person {
  init(name: String, age: Int) {
    self.name = name
    self.age = age
  }

  var name: String = ""
  var age: Int = 0
}

Results in:

Observation Tracking

let p = Person(name: "Tom", age: 12)
withObservationTracking {
  _ = p.name
} onChange: {
  print("Changed!")
}

p.age = 20
print("No log")

p.name = "John"
print("'Changed' is printed")

// No log
// Changed!
// 'Changed' is printed

SwiftUI

There is no way to make it as transparent as SwiftUI 5.0 does. But you can use it with ObservationView:

struct ContentView: View {

  private var person = Person(name: "Tom", age: 12)

  var body: some View {
    ObservationView {
      VStack {
        Text(person.name)
        Text("\(person.age)")
        HStack {
          Button("+") { person.age += 1 }
          Button("-") { person.age -= 1 }
        }
      }
      .padding()
    }
  }
}

Switching to Official Observation Framework

1. Instead of importing ObservationBP, change to import Observation.
2. Add typealias ObservationView = Group to allow the project building. Then remove all ObservationView.

GitHub

View Github