ios - SwiftUI withAnimation 完成回调

Question

我有一个基于某些状态的 swiftUI 动画:

withAnimation(.linear(duration: 0.1)) {
    self.someState = newState
}

上述动画完成时是否会触发任何回调？
如果有关于如何在 SwiftUI 中使用完成 block 完成动画的任何建议，而不是 withAnimation ，我也对这些持开放态度。
我想知道动画何时完成，以便我可以做其他事情，就本示例而言，我只想在动画完成时打印到控制台。

Answer 1

这是一个简化和通用的版本，可用于任何单值动画。这是基于我在等待 Apple 提供更方便的方式时在互联网上找到的其他一些示例:

struct AnimatableModifierDouble: AnimatableModifier {

    var targetValue: Double

    // SwiftUI gradually varies it from old value to the new value
    var animatableData: Double {
        didSet {
            checkIfFinished()
        }
    }

    var completion: () -> ()

    // Re-created every time the control argument changes
    init(bindedValue: Double, completion: @escaping () -> ()) {
        self.completion = completion

        // Set animatableData to the new value. But SwiftUI again directly
        // and gradually varies the value while the body
        // is being called to animate. Following line serves the purpose of
        // associating the extenal argument with the animatableData.
        self.animatableData = bindedValue
        targetValue = bindedValue
    }

    func checkIfFinished() -> () {
        //print("Current value: \(animatableData)")
        if (animatableData == targetValue) {
            //if animatableData.isEqual(to: targetValue) {
            DispatchQueue.main.async {
                self.completion()
            }
        }
    }

    // Called after each gradual change in animatableData to allow the
    // modifier to animate
    func body(content: Content) -> some View {
        // content is the view on which .modifier is applied
        content
        // We don't want the system also to
        // implicitly animate default system animatons it each time we set it. It will also cancel
        // out other implicit animations now present on the content.
            .animation(nil)
    }
}

这是一个关于如何将它与文本不透明动画一起使用的示例:

import SwiftUI

struct ContentView: View {

    // Need to create state property
    @State var textOpacity: Double = 0.0

    var body: some View {
        VStack {
            Text("Hello world!")
                .font(.largeTitle)

                 // Pass generic animatable modifier for animating double values
                .modifier(AnimatableModifierDouble(bindedValue: textOpacity) {

                    // Finished, hurray!
                    print("finished")

                    // Reset opacity so that you could tap the button and animate again
                    self.textOpacity = 0.0

                }).opacity(textOpacity) // bind text opacity to your state property

            Button(action: {
                withAnimation(.easeInOut(duration: 1.0)) {
                    self.textOpacity = 1.0 // Change your state property and trigger animation to start
                }
            }) {
                Text("Animate")
            }
        }
    }
}

struct HomeView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}