如果你因为圆角、子视图和masksToBounds而挣扎，那么尝试使用我的函数:

- (UIView*)putView:(UIView*)view insideShadowWithColor:(UIColor*)color andRadius:(CGFloat)shadowRadius andOffset:(CGSize)shadowOffset andOpacity:(CGFloat)shadowOpacity
{
    CGRect shadowFrame; // Modify this if needed
    shadowFrame.size.width = 0.f;
    shadowFrame.size.height = 0.f;
    shadowFrame.origin.x = 0.f;
    shadowFrame.origin.y = 0.f;
    UIView * shadow = [[UIView alloc] initWithFrame:shadowFrame];
    shadow.userInteractionEnabled = NO; // Modify this if needed
    shadow.layer.shadowColor = color.CGColor;
    shadow.layer.shadowOffset = shadowOffset;
    shadow.layer.shadowRadius = shadowRadius;
    shadow.layer.masksToBounds = NO;
    shadow.clipsToBounds = NO;
    shadow.layer.shadowOpacity = shadowOpacity;
    [view.superview insertSubview:shadow belowSubview:view];
    [shadow addSubview:view];
    return shadow;
}

在你的视图中调用它。无论你的视图是否有圆角，无论它的大小，它的形状-一个漂亮的阴影将被绘制出来。

只要保留函数的返回值，这样当你想要删除表时就可以引用它(或者例如使用insertSubview:aboveView:)

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!

这里是masksToBounds冲突问题的解决方案，它适用于我。

在你设置corderRadius/borderColor/shadow等之后，将masksToBounds设置为NO:

v.layer.masksToBounds = NO;

一种方法是将带有圆角的视图放到带有投影的视图中。

UIView* roundedView = [[UIView alloc] initWithFrame: frame];
roundedView.layer.cornerRadius = 5.0;
roundedView.layer.masksToBounds = YES;

UIView* shadowView = [[UIView alloc] initWithFrame: frame];
shadowView.layer.shadowColor = [UIColor blackColor].CGColor;
shadowView.layer.shadowRadius = 5.0;
shadowView.layer.shadowOffset = CGSizeMake(3.0, 3.0);
shadowView.layer.shadowOpacity = 1.0;
[shadowView addSubview: roundedView];

然后你可以在任何你想要的地方添加shadowView。

检查GitHub上的示例项目，以确保正确使用组件。

简单的Swift 5解决方案，没有任何额外的子视图或子类化:

extension UIView {

    func addShadow(offset: CGSize, color: UIColor, radius: CGFloat, opacity: Float) {
        layer.masksToBounds = false
        layer.shadowOffset = offset
        layer.shadowColor = color.cgColor
        layer.shadowRadius = radius
        layer.shadowOpacity = opacity

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

请注意，在调用addShadow之前，您应该使用角半径和其他属性设置视图。

之后，像这样从viewDidLoad调用这个:

button.addShadow(offset: CGSize.init(width: 0, height: 3), color: UIColor.black, radius: 2.0, opacity: 0.35)

最终结果:

超级简单!

旧线程仍然当前…

我编辑了Daniel Gindi的方法，使它可以用于按钮等。 如果有人需要圆角，或者想要将圆角和边框结合起来，它必须在视图层上设置，这个视图层被传递给这个方法。我还设置了栅格化来加快一点。

+ (UIView*)putView:(UIView*)view insideShadowWithColor:(CGColorRef)color 
                                 andRadius:(CGFloat)shadowRadius 
                                 andOffset:(CGSize)shadowOffset 
                                 andOpacity:(CGFloat)shadowOpacity
{
    // Must have same position like "view"
    UIView *shadow = [[UIView alloc] initWithFrame:view.frame]; 

    shadow.layer.contentsScale = [UIScreen mainScreen].scale;
    shadow.userInteractionEnabled = YES; // Modify this if needed
    shadow.layer.shadowColor = color;
    shadow.layer.shadowOffset = shadowOffset;
    shadow.layer.shadowRadius = shadowRadius;
    shadow.layer.masksToBounds = NO;
    shadow.clipsToBounds = NO;
    shadow.layer.shadowOpacity = shadowOpacity;
    shadow.layer.rasterizationScale = [UIScreen mainScreen].scale;
    shadow.layer.shouldRasterize = YES;

    [view.superview insertSubview:shadow belowSubview:view];
    [shadow addSubview:view];

    // Move view to the top left corner inside the shadowview 
    // ---> Buttons etc are working again :)
    view.frame = CGRectMake(0, 0, view.frame.size.width, view.frame.size.height);

    return shadow;
}