丹尼尔。Gindi上面的回答对我很有用!然而，我不得不做一些小的调整-改变shadowFrame的大小与视图的帧大小相同，并启用用户交互。以下是更新后的代码:

+ (UIView*)putView:(UIView*)view insideShadowWithColor:(UIColor*)color andRadius:(CGFloat)shadowRadius andOffset:(CGSize)shadowOffset andOpacity:(CGFloat)shadowOpacity
{
    CGRect shadowFrame; // Modify this if needed

    // Modified this line
    shadowFrame.size = CGSizeMake(view.frame.size.width, view.frame.size.height);

    shadowFrame.origin.x = 0.f;
    shadowFrame.origin.y = 0.f;
    UIView * shadow = [[UIView alloc] initWithFrame:shadowFrame];

    // Modified this line
    shadow.userInteractionEnabled = YES;
    shadow.layer.shadowColor = color.CGColor;
    shadow.layer.shadowOffset = shadowOffset;
    shadow.layer.shadowRadius = shadowRadius;
    shadow.layer.masksToBounds = NO;
    shadow.clipsToBounds = NO;
    shadow.layer.shadowOpacity = shadowOpacity;

    [shadow addSubview:view];
    return shadow;
}

我想补充的是，在我的情况下，我试图将此添加到第三方视图控制器，即我没有对代码的直接控制。下面是我如何使用上面的函数:

UIView *shadow = [self putView:vc.view 
         insideShadowWithColor:[UIColor blackColor]
                     andRadius:5.0 
                     andOffset:CGSizeMake(0.0, 0.0) 
                    andOpacity:1.0];
vc.view = shadow;
vc.view.layer.cornerRadius = 5.0;
vc.view.layer.masksToBounds = YES;

extension UIView {
    func dropRoundedShadowForAllSides() {
        let backgroundView = UIView(frame:self.frame)
        let radius = frame.height/2
        backgroundView.layer.masksToBounds = false
        self.layer.masksToBounds = true
        backgroundView.layer.shadowOffset = CGSize(width: 0.0, height: 0.0)
        backgroundView.layer.shadowRadius = 4
        backgroundView.layer.shadowOpacity = 0.4

        let path = UIBezierPath()

        // Start at the Top Left Corner + radius distance
        path.move(to: CGPoint(x: 2*radius, y: 0.0))

        // Move to the Top Right Corner - radius distance
        path.addLine(to: CGPoint(x: backgroundView.frame.size.width - radius, y: 0.0))

        // Move to top right corner + radius down as curve
        let centerPoint1 = CGPoint(x:backgroundView.frame.size.width - radius,y:radius)
        path.addArc(withCenter: centerPoint1, radius: radius, startAngle: 3*(.pi/2), endAngle: 0, clockwise: true)

        // Move to the Bottom Right Corner - radius
        path.addLine(to: CGPoint(x: backgroundView.frame.size.width, y: backgroundView.frame.size.height - radius))

        // Move to top right corner + radius left as curve
        let centerPoint2 = CGPoint(x:backgroundView.frame.size.width - radius,y:backgroundView.frame.size.height - radius)
        path.addArc(withCenter: centerPoint2, radius: radius, startAngle: 0, endAngle: .pi/2, clockwise: true)

        // Move to the Bottom Left Corner - radius
        path.addLine(to: CGPoint(x: radius, y: backgroundView.frame.size.height))

        // Move to left right corner - radius up as curve
        let centerPoint3 = CGPoint(x:radius,y:backgroundView.frame.size.height - radius)
        path.addArc(withCenter: centerPoint3, radius: radius, startAngle: .pi/2, endAngle: .pi, clockwise: true)

        // Move to the top Left Corner - radius
        path.addLine(to: CGPoint(x: 0, y: radius))

        // Move to top right corner + radius down as curve
        let centerPoint4 = CGPoint(x:radius,y:radius)
        path.addArc(withCenter: centerPoint4, radius: radius, startAngle: .pi, endAngle: 3 * (.pi/2), clockwise: true)

        path.close()

        backgroundView.layer.shadowPath = path.cgPath
        if let superView = self.superview {
            superView.addSubview(backgroundView)
            superView.sendSubview(toBack: backgroundView)
            superView.bringSubview(toFront: self)
        }

    }
}

iOS阴影和拐角半径

[iOS CALayer]

[iOS masksToBounds]

[iOS调试渲染]

你可以使用图层设置阴影

view1.layer.shadowColor = UIColor.magenta.cgColor

view1.layer.shadowOffset = CGSize(width: 0, height: 0)
view1.layer.shadowOpacity = 1
view1.layer.shadowRadius = 0

可视化

1. shadowoffset。宽度,2. shadowoffset。高度,3。shadowOpacity 4。shadowRadius

shadowOffset宽度和高度是任意的 shadowOpacity从0到1 shadowRadius从0开始为正

不是简单的任务

请注意，阴影不是仅根据边界和边角raduis计算的。在创建阴影的过程中，需要考虑以下事项:

子视图层 子层 内容(支持图像)

view1.backgroundColor = .clear
view1.layer.contents = UIImage(named: "ring")?.cgImage
view1.layer.contentsScale = UIScreen.main.scale

ScaleFactor(contentsScale, rasterizationScale) -默认为1.0

currentBitmapSize = layerSize * scaleFactor

//non retina
1 point == 1x pixels

//Retina
1 point == 2x pixels
//or
1 point == 3x pixels

//For example to draw line 
point(width: 4, height: 2) == 1x pixels(width: 4, height: 2)(8 pixels) == 2x pixels(width: 8, height: 4)(32 pixels)

使用uisscreen .main.scale =当前屏幕的缩放因子

[iOS像素、点数、单位]

的绩效

使用层。角半径，阴影有一些性能影响

至于层。cornerRadius性能:

应用它的颜色混合使用[阅读更多]

至于影子Xcode提示你:

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

1. 另外使用shadowPath

用于内部静态层。默认情况下，它是nil，这就是为什么UIKit应该创建一个屏幕外视图，并基于这个信息创建一个阴影。这就是为什么您能够预定义路径并进行设置。另一个优点是，您可以根据需要创建自定义阴影

view1.layer.shadowPath = UIBezierPath(roundedRect: view1.bounds, cornerRadius: 50).cgPath

缺点-缺乏活力。如果视图改变边界(宽度，高度，角半径…)，阴影仍然是它是(旧的边界)。如果视图的位置被改变(移动，滚动)，shadowPath将是正确的

2. 缓存栅格化

(iOS shouldRasterize)

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

我写了这个UIView分类方法来解决这个问题，使用单独的视图来表示阴影和角的半径。

-(UIView *)shadowedWrapViewWithBounds:(CGRect)bounds {
UIView *baseView = [[UIView alloc] init];
baseView.bounds = bounds;
baseView.backgroundColor = [UIColor clearColor];
baseView.layer.shadowColor = [UIColor blackColor].CGColor;
baseView.layer.shadowOffset = CGSizeMake(0, 0);
baseView.layer.shadowOpacity = 0.7;
baseView.layer.shadowRadius = 4.0;

// improve performance
baseView.layer.shadowPath = [UIBezierPath bezierPathWithRoundedRect:baseView.bounds cornerRadius:4].CGPath;
baseView.layer.shouldRasterize = YES;
baseView.layer.rasterizationScale = [UIScreen mainScreen].scale;

[baseView addSubview:self];
//use Masonry autolayout, self can set corner radius
[self makeConstraints:^(MASConstraintMaker *make) {
    make.edges.equalTo(baseView);
}];

return baseView;
}

Evan Mulawski提供的答案将会非常有效。问题是你必须将视图的背景色设置为clearColor，并将masksToBounds属性设置为NO。

你可以为视图设置任何你想要的颜色

v.layer.backgroundColor = your color;

希望这能有所帮助。