我有一个基于某种状态的 swiftUI 动画：
withAnimation(.linear(duration: 0.1)) {
self.someState = newState
}
上面的动画完成时有没有触发回调？
如果有任何关于如何在 SwiftUI 中使用完成块而不是 withAnimation 来完成动画的建议，我也愿意接受。
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。
【问题讨论】：
标签： ios swift animation swiftui ios13
Guy Javier 在这个博客上描述了如何使用 GeometryEffect 来获得动画反馈，在他的示例中，他检测到动画何时达到 50%，因此他可以翻转视图并使其看起来像有 2 个边
这里有很多解释的全文链接：https://swiftui-lab.com/swiftui-animations-part2/
我将在此处复制相关的 sn-ps，因此即使链接不再有效，答案仍然可以相关：
在此示例中，@Binding var flipped: Bool 在角度介于 90 和 270 之间时变为真，然后变为假。
struct FlipEffect: GeometryEffect {
var animatableData: Double {
get { angle }
set { angle = newValue }
}
@Binding var flipped: Bool
var angle: Double
let axis: (x: CGFloat, y: CGFloat)
func effectValue(size: CGSize) -> ProjectionTransform {
// We schedule the change to be done after the view has finished drawing,
// otherwise, we would receive a runtime error, indicating we are changing
// the state while the view is being drawn.
DispatchQueue.main.async {
self.flipped = self.angle >= 90 && self.angle < 270
}
let a = CGFloat(Angle(degrees: angle).radians)
var transform3d = CATransform3DIdentity;
transform3d.m34 = -1/max(size.width, size.height)
transform3d = CATransform3DRotate(transform3d, a, axis.x, axis.y, 0)
transform3d = CATransform3DTranslate(transform3d, -size.width/2.0, -size.height/2.0, 0)
let affineTransform = ProjectionTransform(CGAffineTransform(translationX: size.width/2.0, y: size.height / 2.0))
return ProjectionTransform(transform3d).concatenating(affineTransform)
}
}
您应该能够将动画更改为您想要实现的任何内容，然后在完成后获取绑定以更改父级的状态。
【讨论】：
您需要使用自定义修饰符。
我已经做了一个例子，用一个完成块为 X 轴上的偏移设置动画。
struct OffsetXEffectModifier: AnimatableModifier {
var initialOffsetX: CGFloat
var offsetX: CGFloat
var onCompletion: (() -> Void)?
init(offsetX: CGFloat, onCompletion: (() -> Void)? = nil) {
self.initialOffsetX = offsetX
self.offsetX = offsetX
self.onCompletion = onCompletion
}
var animatableData: CGFloat {
get { offsetX }
set {
offsetX = newValue
checkIfFinished()
}
}
func checkIfFinished() -> () {
if let onCompletion = onCompletion, offsetX == initialOffsetX {
DispatchQueue.main.async {
onCompletion()
}
}
}
func body(content: Content) -> some View {
content.offset(x: offsetX)
}
}
struct OffsetXEffectModifier_Previews: PreviewProvider {
static var previews: some View {
ZStack {
Text("Hello")
.modifier(
OffsetXEffectModifier(offsetX: 10, onCompletion: {
print("Completed")
})
)
}
.frame(width: 100, height: 100, alignment: .bottomLeading)
.previewLayout(.sizeThatFits)
}
}
【讨论】：
这里有一点简化和通用的版本，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)
}
}
下面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()
}
}
【讨论】：
很遗憾，这个问题还没有很好的解决方案。
但是，如果您可以指定Animation 的持续时间，您可以使用DispatchQueue.main.asyncAfter 在动画结束时准确触发动作：
withAnimation(.linear(duration: 0.1)) {
self.someState = newState
}
DispatchQueue.main.asyncAfter(deadline: .now() + 0.1) {
print("Animation finished")
}
【讨论】：
你可以试试VDAnimation library
Animate(animationStore) {
self.someState =~ newState
}
.duration(0.1)
.curve(.linear)
.start {
...
}
【讨论】：