Optimization Opportunities: The layer is using dynamic shadows which are expensive to render. If possible try setting shadowPath, or pre-rendering the shadow into an image and putting it under the layer.

这是因为没有设置shadowPath导致了离屏渲染
解决方法有两种：

  1. 通过明确地设置shadowPath来“引导”阴影渲染，例如
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view.layer.shadowPath = UIBezierPath(rect: view.bounds).cgPath
  1. 缓存rasterization(珊格化)
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view.layer.shouldRasterize = true
view.layer.rasterizationScale = UIScreen.main.scale