Christopher Campbell JensenMar 1, 2023
Luca Bernardi

While talking to developers we get a lot of questions on how to initialize a @StateObject with external values.

Today we update our docs by greatly expanding around all our data flow primitives with special attention to StateObject. You'll find better explanations on how to initialize StateObject with external data and few words around what to pay attention when doing so (https://developer.apple.com/documentation/swiftui/stateobject)

We hope this helps everyone get more clarity and understanding on how to work with SwiftUI.

StateObject | Apple Developer Documentation

A property wrapper type that instantiates an observable object.

Apple Developer Documentation
Mar 1, 2023 at 4:06pmIvory for Mac
Show threadPaul HudsonMar 1, 2023
@lucabernardi That is so much clearer now, and I love that it documents trickier use cases - please pass on my thanks to the writers! 🙌
Show threadŁukasz KuczborskiMar 1, 2023
@lucabernardi Thanks!
Show threadcalicodingMar 1, 2023
@lucabernardi wonderful! Documentation is often a thankless task, but it has a huge impact on developer satisfaction. So thank you!
Show threadThomas RicouardMar 1, 2023
@lucabernardi This is amazing!
Show threadRicardo CarvalhoMar 1, 2023
@lucabernardi thanks for that! We are introducing SwiftUI in a project now and I had some concerns about the best way to use @StateObject, that will be helpful.
Show threadDimitri GianiMar 1, 2023

@lucabernardi great article!
Just update the model with initializer, otherwise the MyInitializableView do not works:

class DataModel: ObservableObject {
@Published var name = "Some Name"
@Published var isEnabled = false

init(name: String = "Some Name", isEnabled: Bool = false) {
self.name = name
self.isEnabled = isEnabled
}
}

Show threadChris Wu 🪐Mar 1, 2023
@lucabernardi Thanks for the heads up Luca! Code examples are always appreciated.
Show threadKevin ClarkMar 1, 2023
@lucabernardi This is great! Excited to see more focus on documentation 👏
Show threadandreaskernMar 1, 2023
@lucabernardi Thank you for adapting the documentation to real world scenarios.
Show threadD.B. Galeli 🔱 Mar 1, 2023
@lucabernardi Amazing! Thanks, this is so helpful!
Show threadHannes OudMar 1, 2023
@lucabernardi this quality of documentation makes a big difference, thanks for putting in the work!
Show threadAlexandre ColucciMar 1, 2023
@lucabernardi This is so much better, thanks 🙏
Show threadAdam Bell Mar 1, 2023
@lucabernardi thanks!!
Show threadJaanus KaseMar 2, 2023

@lucabernardi thank you so much for this! Glad to see that it reflects discussions I’ve soon on Ask Apple and here on Mastodon.

One thing that’s new to me is the autoclosure in the StateObject initializer with external value. I understand what it does for simple data types.

Does the autoclosure in initializer work the same way for richer and more stateful objects? I have to test my setup a bit and find out.

Show threadLukas ValentaMar 10, 2023
@lucabernardi @heyjaywilson and same applies for State?
Show threadMalcolm HallMar 25, 2023
@lucabernardi I think the developers that asked these questions don't understand that @StateObject is a source of truth (the reference type equivalent of @State) so should not depend on any initialisation parameters. If it needs a parameter, it should simply be moved up in the hierarchy so its properties can be set. It is extremely likely these developers are misusing @StateObject for a legacy view model object instead of learning the View struct's features like diffing and dependency tracking.
Show threadAndy IbanezMar 25, 2023
@malhal @lucabernardi as someone who has asked this question in the past, I completely understand the point that @StateObject is like @State but for reference types now. I think it’s worth a discussion and how the alternatives may be used, especially for those looking into injecting values into the view model without having to rely on optionals.