如何在swift中将阴影仅添加到UIVIEW顶部和底部

在Swift中，可以通过以下步骤将阴影仅添加到UIView的顶部和底部：

创建一个UIView对象，并设置其frame和其他属性，如背景色、圆角等。

let shadowView = UIView(frame: CGRect(x: 0, y: 0, width: 200, height: 100))
shadowView.backgroundColor = UIColor.white
shadowView.layer.cornerRadius = 10

创建一个CALayer对象，并设置其阴影属性，如颜色、偏移量、透明度等。

let shadowLayer = CALayer()
shadowLayer.shadowColor = UIColor.black.cgColor
shadowLayer.shadowOffset = CGSize(width: 0, height: 2)
shadowLayer.shadowOpacity = 0.5

设置CALayer的阴影路径为UIView的顶部和底部边界。

let shadowPath = UIBezierPath()
shadowPath.move(to: CGPoint(x: 0, y: 0))
shadowPath.addLine(to: CGPoint(x: shadowView.bounds.width, y: 0))
shadowPath.move(to: CGPoint(x: 0, y: shadowView.bounds.height))
shadowPath.addLine(to: CGPoint(x: shadowView.bounds.width, y: shadowView.bounds.height))
shadowLayer.shadowPath = shadowPath.cgPath

将CALayer添加到UIView的layer中。

shadowView.layer.addSublayer(shadowLayer)

完整的代码示例：

import UIKit

let shadowView = UIView(frame: CGRect(x: 0, y: 0, width: 200, height: 100))
shadowView.backgroundColor = UIColor.white
shadowView.layer.cornerRadius = 10

let shadowLayer = CALayer()
shadowLayer.shadowColor = UIColor.black.cgColor
shadowLayer.shadowOffset = CGSize(width: 0, height: 2)
shadowLayer.shadowOpacity = 0.5

let shadowPath = UIBezierPath()
shadowPath.move(to: CGPoint(x: 0, y: 0))
shadowPath.addLine(to: CGPoint(x: shadowView.bounds.width, y: 0))
shadowPath.move(to: CGPoint(x: 0, y: shadowView.bounds.height))
shadowPath.addLine(to: CGPoint(x: shadowView.bounds.width, y: shadowView.bounds.height))
shadowLayer.shadowPath = shadowPath.cgPath

shadowView.layer.addSublayer(shadowLayer)

这样，你就可以在UIView的顶部和底部添加阴影了。