# published value

[SwiftUI](https://lochiwei.gitbook.io/ios/swiftui) ⟩ [view](https://lochiwei.gitbook.io/ios/swiftui/view) ⟩ [state](https://lochiwei.gitbook.io/ios/swiftui/view/state) ⟩ [observable object](https://lochiwei.gitbook.io/ios/swiftui/view/state/observable-object) ⟩ published value

{% hint style="success" %}
In an [observable object](https://lochiwei.gitbook.io/ios/swiftui/view/state/observable-object/observableobject), a [property](https://lochiwei.gitbook.io/ios/swift/type/prop) <mark style="color:yellow;">declared</mark> by adding <mark style="color:orange;">@Published</mark> [property wrapper](https://lochiwei.gitbook.io/ios/swift/type/prop/wrapper) that <mark style="color:yellow;">notifies</mark> all [observers](https://lochiwei.gitbook.io/ios/swiftui/view/state/observable-object/observer) <mark style="color:yellow;">when its value is</mark> <mark style="color:red;">about</mark> <mark style="color:yellow;">to change</mark>. When the value changes, SwiftUI <mark style="color:yellow;">updates</mark> all [views](https://lochiwei.gitbook.io/ios/swiftui/view) that <mark style="color:yellow;">use its data</mark>. Also called a <mark style="color:purple;">published property</mark>.
{% endhint %}

```swift
// ⭐️ 1. declare an observable object type
class CreatureZoo : ObservableObject {

    // ⭐️ 2. declare published value(s)
    @Published var creatures = [
        Creature(name: "Gorilla", emoji: "🦍"),    // `Creature` is a custom type
        Creature(name: "Peacock", emoji: "🦚"),
    ]
    
}

// content view
struct ContentView: View {

    // ⭐️ 3. initialize an observable object
    @StateObject var data = CreatureZoo()
    
    var body: some View {
        // ⭐️ 4. access `data.creatures` in subviews
    }
}
```

{% tabs %}
{% tab title="👥 相關" %}

* [observableobject](https://lochiwei.gitbook.io/ios/swiftui/view/state/observable-object/observableobject "mention")：declare an <mark style="color:yellow;">observable object</mark> [type](https://lochiwei.gitbook.io/ios/swift/type).
* [published](https://lochiwei.gitbook.io/ios/swiftui/view/state/observable-object/published "mention")：declare a <mark style="color:purple;">published value</mark> in an [observable object](https://lochiwei.gitbook.io/ios/swiftui/view/state/observable-object/observableobject) type.
* [stateobject](https://lochiwei.gitbook.io/ios/swiftui/view/state/object/stateobject "mention")：initialize an observable object.
  {% endtab %}

{% tab title="📘 手冊" %}

* [Combine](https://developer.apple.com/documentation/combine) ⟩ [Published](https://developer.apple.com/documentation/combine/published)
  {% endtab %}
  {% endtabs %}


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