🅿️View

SwiftUI ⟩ Views ⟩ View ⟩

⭐️ 重點

Views are copied frequently, two rules in mind when designing views:

• Make initialization cheap.

• Make body a pure function, free of side effects. Simply create your view and return, no dispatching extra work.

📍屬性

• .getSize() - do something with view's size.

• .onChangeSize() - do something when view's size is changed.

🔸 定義

@available(iOS 13.0, macOS 10.15, tvOS 13.0, watchOS 6.0, *)
public protocol View {

    /// inferred from implementation of `body`.
    associatedtype Body : View

    /// view body
    @ViewBuilder var body: Self.Body { get }
}

⭐️ 注意：.body 是一個 ViewBuilder❗( Swift 5.3 ) ️👉 Paul

📜 協定

📘 手冊

• SwiftUI ⟩ Views and Controls ⟩

  • Declaring a Custom View

  • View (protocol) ⟩ .body

📗 參考

• Vadim ⟩ SwiftUI View Lifecycle

• Paul ⟩ Why does SwiftUI use “some View” for its view type? (about associated type View.Body, ViewBuilder)

• Sundell ⟩

  • The lifecycle and semantics of a SwiftUI view

  • Using multiple computed properties to form a SwiftUI view’s body

👥 相關

• Opaque Types

• features: .body is a ViewBuilder. ( Swift 5.3 )

💈範例

• BinaryBitPatternView - custom view for floating-point numbers.