Transition

protocol · iOS 17.0+ · SDK 27.1

@MainActor @preconcurrency protocol Transition

A description of view changes to apply when a view is added to and removed from the view hierarchy. A transition should generally be made by applying one or more modifiers to the `content`. For symmetric transitions, the `isIdentity` property on `phase` can be used to change the properties of modifiers. For asymmetric transitions, the phase itself can be used to change those properties. Transitions should not use any identity-affecting changes like `.id`, `if`, and `switch` on the `content`, since doing so would reset the state of the view they're applied to, causing wasted work and potentially surprising behavior when it appears and disappears. The following code defines a transition that can be used to change the opacity and rotation when a view appears and disappears. struct RotatingFadeTransition: Transition { func body(content: Content, phase: TransitionPhase) -> some View { content .opacity(phase.isIdentity ? 1.0 : 0.0) .rotationEffect(phase.rotation) } } extension TransitionPhase { fileprivate var rotation: Angle { switch self { case .willAppear: return .degrees(30) case .identity: return .zero case .didDisappear: return .degrees(-30) } } } A type conforming to this protocol inherits `@preconcurrency @MainActor` isolation from the protocol if the conformance is included in the type's base declaration: struct MyCustomType: Transition { // `@preconcurrency @MainActor` isolation by default } Isolation to the main actor is the default, but it's not required. Declare the conformance in an extension to opt out of main actor isolation: extension MyCustomType: Transition { // `nonisolated` by default } - See Also: `TransitionPhase` - See Also: `AnyTransition`

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