What does the attribute `@EnvironmentObject` mean in the SwiftUI?

Related searches

As you can see in the official tutorial project, there is this strange @EnvironmentObject placed before var. What does it mean?

struct LandmarkDetail: View {
    @EnvironmentObject var userData: UserData
    var landmark: Landmark

    var landmarkIndex: Int {
        userData.landmarks.firstIndex(where: { $0.id == landmark.id })!
    }
    // ...
}

That's for example for Network purposes. You have a class conforming to BindableObject (Beta 5: ObservableObject) and send through the PassthroughSubject (Beta 5: @Published) your data.

For example this case:

SwiftUI (1.0)

struct Course: Decodable {
    let name: String
}

class NetworkManager: ObservableObject {

    @Published var courses = [Course]()

    func getAllCourses() {
        guard let url = URL(string: "https://api.letsbuildthatapp.com/jsondecodable/courses") else { return }
        URLSession.shared.dataTask(with: url) { (data, response, error) in
            do {
                let courses = try JSONDecoder().decode([Course].self, from: data!)
                DispatchQueue.main.async {
                    self.courses = courses
                }
            } catch {
                print("Failed To decode: ", error)
            }
        }.resume() // VERY IMPORTANT! As the request won't run
    }
}

struct ContentView : View {
    @ObservedObject var networkManager: NetworkManager = NetworkManager()
    // Or this
    // @EnvironmentObject var networkManager: NetworkManager // Don't forget to instaniate it with .environmentObject()

    var body: some View {
        VStack {
            Button(action: {
                self.networkManager.getAllCourses()
            }, label: {
                Text("Get All Courses")
            })

            List(networkManager.courses, id: \.name) {
                Text($0.name)
            }
        }
    }
}

Beta

struct Course: Decodable {
    let name: String
}

class NetworkManager: BindableObject {
    let didChange = PassthroughSubject<NetworkManager, Never>()

    var courses = [Course]() {
        didSet {
            didChange.send(self)
        }
    }

    func getAllCourses() {
        guard let url = URL(string: "https://api.letsbuildthatapp.com/jsondecodable/courses") else { return }
        URLSession.shared.dataTask(with: url) { (data, response, error) in
            do {
                let courses = try JSONDecoder().decode([Course].self, from: data!)
                DispatchQueue.main.async {
                    self.courses = courses
                }
            } catch {
                print("Failed To decode: ", error)
            }
        }.resume() // VERY IMPORTANT! As the request won't run
    }
}

struct ContentView : View {
    @EnvironmentObject var networkManager: NetworkManager

    var body: some View {
        VStack {
            Button(action: {
                self.networkManager.getAllCourses()
            }, label: {
                Text("Get All Courses")
            })

            List(networkManager.courses.identified(by: \.name)) {
                Text($0.name)
            }
        }
    }
}

What does the attribute `@EnvironmentObject` mean in the SwiftUI , 0. EnvironmentObject. I have found from apple document. Description from apple: A dynamic view property that uses a bindable object supplied by an ancestor view to invalidate the current view whenever the bindable object changes. Think of @EnvironmentObject as a smarter, simpler way of using @ObservedObject on lots of views. Rather than creating some data in view A, then passing it to view B, then view C, then view D before finally using it, you can create it in view and put it into the environment so that views B, C, and D will automatically have access to it.

EnvironmentObject

I have found from apple document.

Description from apple:

A dynamic view property that uses a bindable object supplied by an ancestor view to invalidate the current view whenever the bindable object changes.

apple doc

My understanding is when ever we set a value or object was init. Ex: List. When we reload a List some showed View Objects are replaced and removed.

How to use @EnvironmentObject to share data between views, Note: Environment objects must be supplied by an ancestor view – if SwiftUI can't find an environment object of the correct type you'll get a� SwiftUI is all about handling states in order to change or manipulate views. We get three ways to store states in our application. @State @ObservedObject @EnvironmentObject; EnvironmentObject is a way to handle state throughout multiple views in your application. Think of this as a property that you want to keep in sync, no matter on which

It is a BindableObject which SwiftUI will use to determine how to refresh your views via accessing the object. Check out the UserData class in the example. Any child of the view that declares the environmental object will have access to it. In this case userData.

Understanding SwiftUI Data Flow. A primer on some key protocols , It will wrap your object into a dynamic view property, allow SwiftUI to This means that when you create a NotificationBadge view you need to pass The @ EnvironmentObject is a property wrapper, which you can use if you� SwiftUI provides us with a quick and easy way to pass models and services down the View hierarchy, the EnvironmentObject. Just add your model or service to your view as an environmentObject view…

It’s designed to give your views access to the model automatically without the need for dependency injection.

Set the environment object once in the scene delegate then all views in the hierarchy have access to it via their own magic property. I believe it is also possible for a view to override the object for its children but I’ve not yet tested that yet.

SwiftUI Data Flow, Now, what this all means is that by making property @Published , you are able to marked with the `@Published` attribute. public struct Publisher : Combine. @ Binding , or @EnvironmentObject , just as you would expect. Stack Overflow Public questions and answers; Teams Private questions and answers for your team; Enterprise Private self-hosted questions and answers for your enterprise; Jobs Programming and related technical career opportunities

EnvironmentObject, @frozen @propertyWrapper struct EnvironmentObject<ObjectType> where A wrapper of the underlying environment object that can create bindings to its� The nonobjc attribute tells the compiler to make the declaration unavailable in Objective-C code, even though it’s possible to represent it in Objective-C. Applying this attribute to an extension has the same effect as applying it to every member of that extension that isn’t explicitly marked with the objc attribute.

Updated for Xcode 12.0. State is inevitable in any modern app, but with SwiftUI it’s important to remember that all of our views are simply functions of their state – we don’t change the views directly, but instead manipulate the state and let that dictate the result.

To receive the latest developer news, visit and subscribe to our News and Updates.

Comments
  • Related: developer.apple.com/documentation/swiftui/environmentobject
  • I've tried to play a bit with your example but I have these Use of unresolved identifier 'PassthroughSubject' and Type 'NetworkManager' does not conform to protocol 'BindableObject' errors.
  • You need to import Combine a new framework by apple
  • Oh sorry I havent noticed I forgot the import. Could you tell me more about the BindableObject protocol ? I have hard time to understand what it actually does... :/
  • @Que20 Please accept my answer. @ObjectBinding is an External reference property. Actually it is your data model that should be displayed. @EnvironmentObject - the same as @ObjectBinding, but it uses across the environment to other views, while @ObjectBinding should passed explicitly
  • Thank a lot this save me lot of time. I was following all the old code with passthroughtsubject which doesn't work at all in latest betas.