这里有一个肯定有效的解决方案!

我已经创建了UIView扩展所需的边应用阴影如下

enum AIEdge:Int {
    case
    Top,
    Left,
    Bottom,
    Right,
    Top_Left,
    Top_Right,
    Bottom_Left,
    Bottom_Right,
    All,
    None
}

extension UIView {
        
    func applyShadowWithCornerRadius(color:UIColor, opacity:Float, radius: CGFloat, edge:AIEdge, shadowSpace:CGFloat, cornerRadius: CGFloat)    {

        var sizeOffset:CGSize = CGSize.zero
        
        switch edge {
        case .Top:
            sizeOffset = CGSize(width: 0, height: -shadowSpace)
        case .Left:
            sizeOffset = CGSize(width: -shadowSpace, height: 0)
        case .Bottom:
            sizeOffset = CGSize(width: 0, height: shadowSpace)
        case .Right:
            sizeOffset = CGSize(width: shadowSpace, height: 0)
            
            
        case .Top_Left:
            sizeOffset = CGSize(width: -shadowSpace, height: -shadowSpace)
        case .Top_Right:
            sizeOffset = CGSize(width: shadowSpace, height: -shadowSpace)
        case .Bottom_Left:
            sizeOffset = CGSize(width: -shadowSpace, height: shadowSpace)
        case .Bottom_Right:
            sizeOffset = CGSize(width: shadowSpace, height: shadowSpace)
            
            
        case .All:
            sizeOffset = CGSize(width: 0, height: 0)
        case .None:
            sizeOffset = CGSize.zero
        }

        self.layer.cornerRadius = cornerRadius
        self.layer.masksToBounds = true

        self.layer.shadowColor = color.cgColor
        self.layer.shadowOpacity = opacity
        self.layer.shadowOffset = sizeOffset
        self.layer.shadowRadius = radius
        self.layer.masksToBounds = false

        self.layer.shadowPath = UIBezierPath(roundedRect:self.bounds, cornerRadius:self.layer.cornerRadius).cgPath
    }
}

最后，你可以为你的UIView子类调用下面的阴影函数，你也可以指定边缘上应用阴影，尝试不同的变化根据你需要改变下面方法调用的参数。

viewRoundedToBeShadowedAsWell.applyShadowWithCornerRadius(color: .gray, opacity: 1, radius: 15, edge: AIEdge.All, shadowSpace: 15)

注意:如果仍然不工作，试着从主线程调用它

DispatchQueue.main.async {
   viewRoundedToBeShadowedAsWell.applyShadowWithCornerRadius(color: .gray, opacity: 1, radius: 15, edge: AIEdge.All, shadowSpace: 15)
}

希望有人觉得这有用!

以下是结果图片:

斯威夫特

// corner radius
blueView.layer.cornerRadius = 10

// border
blueView.layer.borderWidth = 1.0
blueView.layer.borderColor = UIColor.black.cgColor

// shadow
blueView.layer.shadowColor = UIColor.black.cgColor
blueView.layer.shadowOffset = CGSize(width: 3, height: 3)
blueView.layer.shadowOpacity = 0.7
blueView.layer.shadowRadius = 4.0

探索选择

问题1:阴影被剪掉了

如果我们希望将子层或子视图(如图像)的内容剪辑到视图的边界，该怎么办?

我们可以用

blueView.layer.masksToBounds = true

(另外,blueView。clipsToBounds = true给出相同的结果。)

但是，哦不!影子也被剪掉了，因为它在边界之外!怎么办呢?怎么办呢?

解决方案

阴影和边界使用单独的视图。基本视图是透明的，并且有阴影。边界视图将它拥有的任何其他子内容剪辑到它的边界。

// add the shadow to the base view
baseView.backgroundColor = UIColor.clear
baseView.layer.shadowColor = UIColor.black.cgColor
baseView.layer.shadowOffset = CGSize(width: 3, height: 3)
baseView.layer.shadowOpacity = 0.7
baseView.layer.shadowRadius = 4.0

// add the border to subview
let borderView = UIView()
borderView.frame = baseView.bounds
borderView.layer.cornerRadius = 10
borderView.layer.borderColor = UIColor.black.cgColor
borderView.layer.borderWidth = 1.0
borderView.layer.masksToBounds = true
baseView.addSubview(borderView)

// add any other subcontent that you want clipped
let otherSubContent = UIImageView()
otherSubContent.image = UIImage(named: "lion")
otherSubContent.frame = borderView.bounds
borderView.addSubview(otherSubContent)

结果如下:

问题2:表现不佳

添加圆角和阴影可以提高性能。您可以通过为阴影使用预定义的路径并指定它是栅格化来提高性能。下面的代码可以添加到上面的示例中。

baseView.layer.shadowPath = UIBezierPath(roundedRect: baseView.bounds, cornerRadius: 10).cgPath
baseView.layer.shouldRasterize = true
baseView.layer.rasterizationScale = UIScreen.main.scale

更多细节请看这篇文章。看这里和这里。

我们用Swift 4和Xcode 9测试了这个答案。

Swift 3 & IBInspectable解决方案: 灵感来自Ade的解决方案

首先，创建一个UIView扩展:

//
//  UIView-Extension.swift
//  

import Foundation
import UIKit

@IBDesignable
extension UIView {
     // Shadow
     @IBInspectable var shadow: Bool {
          get {
               return layer.shadowOpacity > 0.0
          }
          set {
               if newValue == true {
                    self.addShadow()
               }
          }
     }

     fileprivate func addShadow(shadowColor: CGColor = UIColor.black.cgColor, shadowOffset: CGSize = CGSize(width: 3.0, height: 3.0), shadowOpacity: Float = 0.35, shadowRadius: CGFloat = 5.0) {
          let layer = self.layer
          layer.masksToBounds = false

          layer.shadowColor = shadowColor
          layer.shadowOffset = shadowOffset
          layer.shadowRadius = shadowRadius
          layer.shadowOpacity = shadowOpacity
          layer.shadowPath = UIBezierPath(roundedRect: layer.bounds, cornerRadius: layer.cornerRadius).cgPath

          let backgroundColor = self.backgroundColor?.cgColor
          self.backgroundColor = nil
          layer.backgroundColor =  backgroundColor
     }


     // Corner radius
     @IBInspectable var circle: Bool {
          get {
               return layer.cornerRadius == self.bounds.width*0.5
          }
          set {
               if newValue == true {
                    self.cornerRadius = self.bounds.width*0.5
               }
          }
     }

     @IBInspectable var cornerRadius: CGFloat {
          get {
               return self.layer.cornerRadius
          }

          set {
               self.layer.cornerRadius = newValue
          }
     }


     // Borders
     // Border width
     @IBInspectable
     public var borderWidth: CGFloat {
          set {
               layer.borderWidth = newValue
          }

          get {
               return layer.borderWidth
          }
     }

     // Border color
     @IBInspectable
     public var borderColor: UIColor? {
          set {
               layer.borderColor = newValue?.cgColor
          }

          get {
               if let borderColor = layer.borderColor {
                    return UIColor(cgColor: borderColor)
               }
               return nil
          }
     }
}

然后，在界面构建器中选择你的UIView，设置阴影ON和角半径，如下所示:

结果!

这对我很管用。窍门是将背景颜色从主视图移到图层中。

CALayer *layer = view.layer;
layer.cornerRadius = 15.0f;
layer.masksToBounds = NO;

layer.shadowOffset = CGSizeMake(0, 3);
layer.shadowColor = [[UIColor blackColor] CGColor];
layer.shadowRadius = 2.0f;
layer.shadowOpacity = 0.35f;
layer.shadowPath = [[UIBezierPath bezierPathWithRoundedRect:layer.bounds cornerRadius:layer.cornerRadius] CGPath];

CGColorRef  bColor = view.backgroundColor.CGColor;
view.backgroundColor = nil;
layer.backgroundColor =  bColor ;

var shadows = UIView()
shadows.frame = view.frame
shadows.clipsToBounds = false
view.addSubview(shadows)


let shadowPath0 = UIBezierPath(roundedRect: shadows.bounds, cornerRadius: 10)
let layer0 = CALayer()
layer0.shadowPath = shadowPath0.cgPath
layer0.shadowColor = UIColor(red: 0, green: 0, blue: 0, alpha: 0.23).cgColor
layer0.shadowOpacity = 1
layer0.shadowRadius = 6
layer0.shadowOffset = CGSize(width: 0, height: 3)
layer0.bounds = shadows.bounds
layer0.position = shadows.center

shadows.layer.addSublayer(layer0)

Swift 4解决方案，使UICollectionViewCell圆形和添加阴影，没有任何扩展和并发症:)

注意:对于简单的视图，例如按钮。请看这篇文章中的@suragch的回答。 https://stackoverflow.com/a/34984063/7698092。按钮测试成功

以防有人还在努力使角落圆润，同时添加阴影。虽然这个解决方案适用于UICollectionViewCell，但它可以推广到任何视图。

这个技巧对我来说很有效，不需要做任何扩展和所有复杂的事情。我正在使用storyBoard。

技术

你必须在storyBoard的UICollectionViewCell中添加一个UIView(让我们说它是“containerView”)，并在这个containerView中添加所有必需的视图(按钮，图像等)。 见截图。

连接containerView的出口。在CellforItemAtIndexPath委托函数中添加以下代码行。

//adds shadow to the layer of cell

cell.layer.cornerRadius = 3.0
    cell.layer.masksToBounds = false
    cell.layer.shadowColor = UIColor.black.cgColor
    cell.layer.shadowOffset = CGSize(width: 0, height: 0)
    cell.layer.shadowOpacity = 0.6

//makes the cell round 

let containerView = cell.containerView!
    containerView.layer.cornerRadius = 8
    containerView.clipsToBounds = true

输出

查看模拟器截图