SwiftUI中能否延迟计算视图移除过渡所用变量的值？

你需要确保移除过渡动画使用的是点击发生时的最新位置，而非视图初始渲染时的位置，这完全可行。以下是两种符合你需求的实现方式，均由父视图控制移除动画：

方案一：通过Binding同步点击位置，确保动画使用最新值 #

1. 父视图中定义@State变量存储点击位置，并以Binding形式传递给RainbowView；
2. 在RainbowView的点击事件中，先更新点击位置，再切换视图状态，并将操作包裹在withAnimation中，保证动画触发时位置已更新；
3. 父视图的过渡动画直接使用该位置作为锚点，SwiftUI会读取动画启动瞬间的最新状态值，而非视图初始化时的固定值。

修改后的核心代码：

// 父视图
struct ParentView: View {
    @ObservedObject var settings: Settings
    @State private var tapLocation: UnitPoint = .center
    
    var body: some View {
        ZStack {
            if settings.showRainbow {
                RainbowView(tapLocation: $tapLocation, settings: settings)
                    .transition(AnyTransition.asymmetric(
                        insertion: .opacity,
                        removal: .scale(scale: 24, anchor: tapLocation)
                    ))
            } else {
                OtherView()
            }
        }
    }
}

// RainbowView
struct RainbowView: View {
    @Binding var tapLocation: UnitPoint
    @ObservedObject var settings: Settings
    
    var body: some View {
        HStack {
            Color.red.onTapGesture { updateTapLocationAndDismiss(location: .leading) }
            Color.green.onTapGesture { updateTapLocationAndDismiss(location: .center) }
            Color.blue.onTapGesture { updateTapLocationAndDismiss(location: .trailing) }
        }
    }
    
    private func updateTapLocationAndDismiss(location: UnitPoint) {
        withAnimation {
            tapLocation = location
            settings.showRainbow = false
        }
    }
}

class Settings: ObservableObject {
    @Published var showRainbow = true
}

方案二：使用PreferenceKey传递点击位置（复杂视图场景更灵活） #

如果RainbowView结构复杂，不想直接传递Binding，可以通过PreferenceKey实现跨视图的位置传递：

1. 定义偏好键用于存储点击位置：

struct TapLocationPreferenceKey: PreferenceKey {
    static var defaultValue: UnitPoint = .center
    static func reduce(value: inout UnitPoint, nextValue: () -> UnitPoint) {
        value = nextValue()
    }
}

2. 在RainbowView的点击事件中发送最新位置：

struct RainbowView: View {
    @ObservedObject var settings: Settings
    
    var body: some View {
        HStack {
            Color.red.onTapGesture {
                sendTapLocation(.leading)
                dismiss()
            }
            Color.green.onTapGesture {
                sendTapLocation(.center)
                dismiss()
            }
            Color.blue.onTapGesture {
                sendTapLocation(.trailing)
                dismiss()
            }
        }
    }
    
    private func sendTapLocation(_ location: UnitPoint) {
        self.preference(key: TapLocationPreferenceKey.self, value: location)
    }
    
    private func dismiss() {
        withAnimation {
            settings.showRainbow = false
        }
    }
}

3. 父视图接收并更新位置：

struct ParentView: View {
    @ObservedObject var settings: Settings
    @State private var tapLocation: UnitPoint = .center
    
    var body: some View {
        ZStack {
            if settings.showRainbow {
                RainbowView(settings: settings)
                    .transition(AnyTransition.asymmetric(
                        insertion: .opacity,
                        removal: .scale(scale: 24, anchor: tapLocation)
                    ))
                    .onPreferenceChange(TapLocationPreferenceKey.self) { newLocation in
                        tapLocation = newLocation
                    }
            } else {
                OtherView()
            }
        }
    }
}

关键注意点 #

• 必须用withAnimation包裹状态变化，否则过渡动画无法同步状态更新；
• 两种方案的核心都是保证移除动画触发前，点击位置已更新为最新值，SwiftUI会自动使用该值作为动画参数。

内容的提问来源于stack exchange，提问作者Andromeda