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

When you can set iOS 17 or later as your deploy target, you can switch back to the official framework.

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