在当前代码中，保存当前上下文的GState，配置为绘制阴影。然后将其恢复到您配置它绘制阴影之前的状态。然后，最后，调用超类的drawRect:的实现。

任何应该受到阴影设置影响的绘图都需要在之后进行

CGContextSetShadow(currentContext, CGSizeMake(-15, 20), 5);

但在

CGContextRestoreGState(currentContext);

如果你想要超类的drawRect:被“包装”在阴影中，那么如果你像这样重新安排你的代码呢?

- (void)drawRect:(CGRect)rect {
    CGContextRef currentContext = UIGraphicsGetCurrentContext();
    CGContextSaveGState(currentContext);
    CGContextSetShadow(currentContext, CGSizeMake(-15, 20), 5);
    [super drawRect: rect];
    CGContextRestoreGState(currentContext);
}

我把它作为我效用的一部分。有了这个，我们不仅可以设置阴影，还可以为任何UIView获得圆角。你也可以设置你喜欢什么颜色的阴影。通常情况下，黑色是首选，但有时，当背景是非白色时，你可能想要其他颜色。这是我用的-

in utils.m
+ (void)roundedLayer:(CALayer *)viewLayer 
              radius:(float)r 
              shadow:(BOOL)s
{
    [viewLayer setMasksToBounds:YES];
    [viewLayer setCornerRadius:r];        
    [viewLayer setBorderColor:[RGB(180, 180, 180) CGColor]];
    [viewLayer setBorderWidth:1.0f];
    if(s)
    {
        [viewLayer setShadowColor:[RGB(0, 0, 0) CGColor]];
        [viewLayer setShadowOffset:CGSizeMake(0, 0)];
        [viewLayer setShadowOpacity:1];
        [viewLayer setShadowRadius:2.0];
    }
    return;
}

要使用这个，我们需要调用它- [utils roundedLayer:yourview。图层半径:5.0f阴影:YES];

你可以试试这个....你可以调整数值。 阴影半径决定了模糊的数量。shadowOffset指定阴影的位置。

斯威夫特2.0

let radius: CGFloat = demoView.frame.width / 2.0 //change it to .height if you need spread for height
let shadowPath = UIBezierPath(rect: CGRect(x: 0, y: 0, width: 2.1 * radius, height: demoView.frame.height))
//Change 2.1 to amount of spread you need and for height replace the code for height

demoView.layer.cornerRadius = 2
demoView.layer.shadowColor = UIColor.blackColor().CGColor
demoView.layer.shadowOffset = CGSize(width: 0.5, height: 0.4)  //Here you control x and y
demoView.layer.shadowOpacity = 0.5
demoView.layer.shadowRadius = 5.0 //Here your control your blur
demoView.layer.masksToBounds =  false
demoView.layer.shadowPath = shadowPath.CGPath

斯威夫特3.0

let radius: CGFloat = demoView.frame.width / 2.0 //change it to .height if you need spread for height 
let shadowPath = UIBezierPath(rect: CGRect(x: 0, y: 0, width: 2.1 * radius, height: demoView.frame.height)) 
//Change 2.1 to amount of spread you need and for height replace the code for height

demoView.layer.cornerRadius = 2
demoView.layer.shadowColor = UIColor.black.cgColor
demoView.layer.shadowOffset = CGSize(width: 0.5, height: 0.4)  //Here you control x and y
demoView.layer.shadowOpacity = 0.5
demoView.layer.shadowRadius = 5.0 //Here your control your blur
demoView.layer.masksToBounds =  false
demoView.layer.shadowPath = shadowPath.cgPath

关于传播的例子

创建一个基本的阴影

    demoView.layer.cornerRadius = 2
    demoView.layer.shadowColor = UIColor.blackColor().CGColor
    demoView.layer.shadowOffset = CGSizeMake(0.5, 4.0); //Here your control your spread
    demoView.layer.shadowOpacity = 0.5 
    demoView.layer.shadowRadius = 5.0 //Here your control your blur

Swift 2.0中的基本Shadow示例

同样的解决方案，但只是提醒你:你可以直接在故事板中定义阴影。

Ex:

简单和干净的解决方案使用接口生成器

在你的项目中添加一个名为UIView.swift的文件(或者直接粘贴到任何文件中):

import UIKit

@IBDesignable extension UIView {

    /* The color of the shadow. Defaults to opaque black. Colors created
    * from patterns are currently NOT supported. Animatable. */
    @IBInspectable var shadowColor: UIColor? {
        set {
            layer.shadowColor = newValue!.CGColor
        }
        get {
            if let color = layer.shadowColor {
                return UIColor(CGColor:color)
            }
            else {
                return nil
            }
        }
    }

    /* The opacity of the shadow. Defaults to 0. Specifying a value outside the
    * [0,1] range will give undefined results. Animatable. */
    @IBInspectable var shadowOpacity: Float {
        set {
            layer.shadowOpacity = newValue
        }
        get {
            return layer.shadowOpacity
        }
    }

    /* The shadow offset. Defaults to (0, -3). Animatable. */
    @IBInspectable var shadowOffset: CGPoint {
        set {
            layer.shadowOffset = CGSize(width: newValue.x, height: newValue.y)
        }
        get {
            return CGPoint(x: layer.shadowOffset.width, y:layer.shadowOffset.height)
        }
    }

    /* The blur radius used to create the shadow. Defaults to 3. Animatable. */
    @IBInspectable var shadowRadius: CGFloat {
        set {
            layer.shadowRadius = newValue
        }
        get {
            return layer.shadowRadius
        }
    }
}

然后，这将在接口生成器中为实用工具面板>属性检查器中的每个视图可用:

现在你可以很容易地设置阴影。

注: 影子不会在IB中出现，只在运行时出现。 -正如Mazen Kasser所说

对于那些未能实现这一目标的人……确保剪辑子视图(clipsToBounds)未启用

self.layer.masksToBounds = NO;
self.layer.cornerRadius = 8; // if you like rounded corners
self.layer.shadowOffset = CGSizeMake(-15, 20);
self.layer.shadowRadius = 5;
self.layer.shadowOpacity = 0.5;

这将降低应用程序的速度。 添加下面的行可以提高性能，只要你的视图是可见的矩形:

self.layer.shadowPath = [UIBezierPath bezierPathWithRect:self.bounds].CGPath;