Contents

ObservedObject

A property wrapper type that subscribes to an observable object and invalidates a view whenever the observable object changes.

Declaration

@MainActor @propertyWrapper @preconcurrency @frozen struct ObservedObject<ObjectType> where ObjectType : ObservableObject

Overview

Add the @ObservedObject attribute to a parameter of a SwiftUI View when the input is an ObservableObject and you want the view to update when the object’s published properties change. You typically do this to pass a StateObject into a subview.

The following example defines a data model as an observable object, instantiates the model in a view as a state object, and then passes the instance to a subview as an observed object:

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

struct MyView: View {
    @StateObject private var model = DataModel()

    var body: some View {
        Text(model.name)
        MySubView(model: model)
    }
}

struct MySubView: View {
    @ObservedObject var model: DataModel

    var body: some View {
        Toggle("Enabled", isOn: $model.isEnabled)
    }
}

When any published property of the observable object changes, SwiftUI updates any view that depends on the object. Subviews can also make updates to the model properties, like the Toggle in the above example, that propagate to other observers throughout the view hierarchy.

Don’t specify a default or initial value for the observed object. Use the attribute only for a property that acts as an input for a view, as in the above example.

Topics

Creating an observed object

Getting the value

See Also

Creating model data