Ios SwiftUI 动画：为什么容器视图在移动我很难理解这种行为

我正在构建一个简单的旋转圆来加载动画.我让圆圈旋转，但容器视图在动画期间也在向下移动.我想不出是什么原因导致了这种奇怪的行为.

Example:个

白色边框是父视图ZStack.红色边框是我放置的VStack，用来展示这个奇怪的动画.蓝色边框是ZStack，它包含两个设置动画的Circle.

Here is the code:个

struct CustomLoadingView: View {

  let viewWidth: CGFloat = UIScreen.main.bounds.width * 0.5
  let backgroundCircleLineWidth: CGFloat = UIScreen.main.bounds.width * 0.025
  let foregroundCircleLineWidth: CGFloat = UIScreen.main.bounds.width * 0.02

  @State var rotationDegree: Angle = Angle.degrees(0)

  var body: some View {
    VStack(spacing: 0) {
        ZStack {
            Circle()
              .stroke(style: StrokeStyle(lineWidth: backgroundCircleLineWidth))
              .fill(Global.Colors.primary60)
            
            Circle()
              .trim(from: 0, to: 0.15)
              .stroke(style: StrokeStyle(lineWidth: 7, lineCap: .round))
              .fill(Global.Colors.secondary50)
              .rotationEffect(self.rotationDegree)
        }
          .frame(width: viewWidth, height: viewWidth)
          .border(Color.blue)
          .animation(Animation.linear(duration: 4.5).repeatForever(autoreverses: false), value: rotationDegree)
          .onAppear() {
              self.animateLoader()
          }
    }
      .border(Color.red)
}

   func animateLoader() {
      self.rotationDegree = .degrees(720)
   }
}

你知道为什么会发生这种事吗？我怎么才能让它停下来？谢谢.