IOS：如何在 4 侧（上、右、下、左）为 UIView 制作阴影

在 iOS 开发中，我们经常需要给 UIView 添加阴影效果来提升界面的美观性和层次感。通常情况下，我们可以通过设置视图的 layer 属性来实现阴影效果。本文将介绍如何在 UIView 的四个边（上、右、下、左）添加阴影，并提供相应的代码示例。

swift
let shadowView = UIView(frame: CGRect(x: 50, y: 50, width: 200, height: 200))
shadowView.backgroundColor = UIColor.white
// 设置阴影颜色和透明度
shadowView.layer.shadowColor = UIColor.black.cgColor
shadowView.layer.shadowOpacity = 0.5
// 设置阴影偏移量和模糊半径
shadowView.layer.shadowOffset = CGSize(width: 2, height: 2)
shadowView.layer.shadowRadius = 4
self.view.addSubview(shadowView)

swift
let topShadowView = UIView(frame: CGRect(x: 50, y: 300, width: 200, height: 200))
topShadowView.backgroundColor = UIColor.white
topShadowView.layer.shadowColor = UIColor.black.cgColor
topShadowView.layer.shadowOpacity = 0.5
topShadowView.layer.shadowOffset = CGSize(width: 0, height: -2)
topShadowView.layer.shadowRadius = 4
self.view.addSubview(topShadowView)

swift
let rightShadowView = UIView(frame: CGRect(x: 300, y: 50, width: 200, height: 200))
rightShadowView.backgroundColor = UIColor.white
rightShadowView.layer.shadowColor = UIColor.black.cgColor
rightShadowView.layer.shadowOpacity = 0.5
rightShadowView.layer.shadowOffset = CGSize(width: 2, height: 0)
rightShadowView.layer.shadowRadius = 4
self.view.addSubview(rightShadowView)

swift
let bottomShadowView = UIView(frame: CGRect(x: 50, y: 550, width: 200, height: 200))
bottomShadowView.backgroundColor = UIColor.white
bottomShadowView.layer.shadowColor = UIColor.black.cgColor
bottomShadowView.layer.shadowOpacity = 0.5
bottomShadowView.layer.shadowOffset = CGSize(width: 0, height: 2)
bottomShadowView.layer.shadowRadius = 4
self.view.addSubview(bottomShadowView)

swift
let leftShadowView = UIView(frame: CGRect(x: 550, y: 50, width: 200, height: 200))
leftShadowView.backgroundColor = UIColor.white
leftShadowView.layer.shadowColor = UIColor.black.cgColor
leftShadowView.layer.shadowOpacity = 0.5
leftShadowView.layer.shadowOffset = CGSize(width: -2, height: 0)
leftShadowView.layer.shadowRadius = 4
self.view.addSubview(leftShadowView)