WWDC23 SALE: Save 50% on all my Swift books and bundles! >>

What is the @ObservedObject property wrapper?

Paul Hudson    @twostraws   

Updated for Xcode 14.2

SwiftUI gives us the @ObservedObject property wrapper so that views can watch the state of an external object, and be notified when something important has changed. It is similar in behavior to @StateObject, except it must not be used to create objects – use @ObservableObject only with objects that have been created elsewhere, otherwise SwiftUI might accidentally destroy the object.

For example, we might use something like this:

class Order: ObservableObject {
    @Published var items = [String]()

struct ContentView: View {
    @ObservedObject var order: Order

    var body: some View {
        // your code here

That Order class uses @Published so it will automatically send change announcements when items changes, and ContentView uses @ObservedObject to watch for those announcements. Without @ObservedObject the change announcements would be sent but ignored.

Although that looks straightforward enough, it’s worth digging into a few specifics.

First, any type you mark with @ObservedObject must conform to the ObservableObject protocol, which in turn means it must be a class rather than a struct. This isn’t optional – SwiftUI requires us to use a class here.

Second, observed objects are specifically designed for data that is external to your view, which means it might be shared across more than one view. The @ObservedObject property wrapper will automatically make sure the property is watched closely so that important changes will reload any views using it. This also means the data must be created elsewhere, then sent in to your view.

Third, not all properties in an observed object cause views to refresh – you need to decide which properties should send change notifications, either using @Published or custom announcements. Types that conform to ObservableObject are given a default objectWillChange publisher to make custom announcements as needed.

Save 50% in my WWDC23 sale.

SAVE 50% To celebrate WWDC23, all our books and bundles are half price, so you can take your Swift knowledge further without spending big! Get the Swift Power Pack to build your iOS career faster, get the Swift Platform Pack to builds apps for macOS, watchOS, and beyond, or get the Swift Plus Pack to learn advanced design patterns, testing skills, and more.

Save 50% on all our books and bundles!

Similar solutions…

Buy Pro Swift Buy Pro SwiftUI Buy Swift Design Patterns Buy Testing Swift Buy Hacking with iOS Buy Swift Coding Challenges Buy Swift on Sundays Volume One Buy Server-Side Swift Buy Advanced iOS Volume One Buy Advanced iOS Volume Two Buy Advanced iOS Volume Three Buy Hacking with watchOS Buy Hacking with tvOS Buy Hacking with macOS Buy Dive Into SpriteKit Buy Swift in Sixty Seconds Buy Objective-C for Swift Developers Buy Beyond Code

Was this page useful? Let us know!

Average rating: 4.7/5

Unknown user

You are not logged in

Log in or create account

Link copied to your pasteboard.