如何在 UIView 下绘制阴影？

一种更简单的方法是在初始化时设置视图的一些层属性：

self.layer.masksToBounds = NO;
self.layer.shadowOffset = CGSizeMake(-15, 20);
self.layer.shadowRadius = 5;
self.layer.shadowOpacity = 0.5;

您需要导入 QuartzCore。

#import <QuartzCore/QuartzCore.h>

---

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;

这会减慢应用程序的速度。只要您的视图是明显的矩形，添加以下行可以提高性能：

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

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相同的解决方案，但只是提醒您：您可以直接在情节提要中定义阴影。

前任：

https://i.stack.imgur.com/BPrQV.png

---

在您当前的代码中，您保存当前上下文的 GState，将其配置为绘制阴影 .. 并将其恢复到配置为绘制阴影之前的状态。然后，最后，您调用超类的 drawRect: 实现。

任何应该受阴影设置影响的绘图都需要在之后发生

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

但之前

CGContextRestoreGState(currentContext);

因此，如果您希望超类的 drawRect: 被“包裹”在阴影中，那么如果您像这样重新排列您的代码呢？

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

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你可以试试这个....你可以玩这些价值观。 shadowRadius 指示模糊量。 shadowOffset 指示阴影的去向。

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

传播示例

https://i.stack.imgur.com/z4pwm.png

创建基本阴影

    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 中的基本阴影示例

https://i.stack.imgur.com/OjGBu.png

---

使用 Interface Builder 的简单而干净的解决方案

在您的项目中添加一个名为 UIView.swift 的文件（或将其粘贴到任何文件中）：

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 Interface Builder 中为 Utilities Panel > Attributes Inspector 中的每个视图提供：

https://i.stack.imgur.com/N5Uox.png

您现在可以轻松设置阴影。

注意： - 阴影不会出现在 IB 中，仅在运行时出现。 - 正如 Mazen Kasser 所说

对于那些未能使其正常工作的人[...]确保未启用剪辑子视图（clipsToBounds）

---

我将其用作我的实用程序的一部分。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的颜色阴影。通常黑色是首选，但有时，当背景不是白色时，您可能需要其他东西。这是我使用的 -

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;
}

要使用它，我们需要调用它 - [utils roundedLayer:yourview.layer radius:5.0f shadow:YES];

---

斯威夫特 3

extension UIView {
    func installShadow() {
        layer.cornerRadius = 2
        layer.masksToBounds = false
        layer.shadowColor = UIColor.black.cgColor
        layer.shadowOffset = CGSize(width: 0, height: 1)
        layer.shadowOpacity = 0.45
        layer.shadowPath = UIBezierPath(rect: bounds).cgPath
        layer.shadowRadius = 1.0
    }
}

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如果您想使用 StoryBoard 并且不想继续输入运行时属性，您可以轻松地创建视图扩展并使其在 Storyboard 中可用。

步骤 1. 创建扩展

extension UIView {

@IBInspectable var shadowRadius: CGFloat {
    get {
        return layer.shadowRadius
    }
    set {
        layer.shadowRadius = newValue
    }
}

@IBInspectable var shadowOpacity: Float {
    get {
        return layer.shadowOpacity
    }
    set {
        layer.shadowOpacity = newValue
    }
}

@IBInspectable var shadowOffset: CGSize {
    get {
        return layer.shadowOffset
    }
    set {
        layer.shadowOffset = newValue
    }
}

@IBInspectable var maskToBound: Bool {
    get {
        return layer.masksToBounds
    }
    set {
        layer.masksToBounds = newValue
    }
}
}

https://i.stack.imgur.com/UlFpR.png

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对于在此处尝试所有答案后未能使其正常工作的人（作为我自己！），只需确保在属性检查器中未启用剪辑子视图...

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在 Swift 4 中使用 IBDesignable 和 IBInspectable 绘制阴影

如何使用它

https://i.stack.imgur.com/YOobC.gif

并排草图和 XCODE

https://i.stack.imgur.com/gtTgz.png

代码

@IBDesignable class ShadowView: UIView {

    @IBInspectable var shadowColor: UIColor? {
        get {
            if let color = layer.shadowColor {
                return UIColor(cgColor: color)
            }
            return nil
        }
        set {
            if let color = newValue {
                layer.shadowColor = color.cgColor
            } else {
                layer.shadowColor = nil
            }
        }
    }

    @IBInspectable var shadowOpacity: Float {
        get {
            return layer.shadowOpacity
        }
        set {
            layer.shadowOpacity = newValue
        }
    }

    @IBInspectable var shadowOffset: CGPoint {
        get {
            return CGPoint(x: layer.shadowOffset.width, y:layer.shadowOffset.height)
        }
        set {
            layer.shadowOffset = CGSize(width: newValue.x, height: newValue.y)
        }

     }

    @IBInspectable var shadowBlur: CGFloat {
        get {
            return layer.shadowRadius
        }
        set {
            layer.shadowRadius = newValue / 2.0
        }
    }

    @IBInspectable var shadowSpread: CGFloat = 0 {
        didSet {
            if shadowSpread == 0 {
                layer.shadowPath = nil
            } else {
                let dx = -shadowSpread
                let rect = bounds.insetBy(dx: dx, dy: dx)
                layer.shadowPath = UIBezierPath(rect: rect).cgPath
            }
        }
    }
}

输出

https://i.stack.imgur.com/haMSV.png

---

您可以使用我为阴影和角半径创建的实用函数，如下所示：

- (void)addShadowWithRadius:(CGFloat)shadowRadius withShadowOpacity:(CGFloat)shadowOpacity withShadowOffset:(CGSize)shadowOffset withShadowColor:(UIColor *)shadowColor withCornerRadius:(CGFloat)cornerRadius withBorderColor:(UIColor *)borderColor withBorderWidth:(CGFloat)borderWidth forView:(UIView *)view{

    // drop shadow
    [view.layer setShadowRadius:shadowRadius];
    [view.layer setShadowOpacity:shadowOpacity];
    [view.layer setShadowOffset:shadowOffset];
    [view.layer setShadowColor:shadowColor.CGColor];

    // border radius
    [view.layer setCornerRadius:cornerRadius];

    // border
    [view.layer setBorderColor:borderColor.CGColor];
    [view.layer setBorderWidth:borderWidth];
}

希望对你有帮助！！！

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斯威夫特 3

self.paddingView.layer.masksToBounds = false
self.paddingView.layer.shadowOffset = CGSize(width: -15, height: 10)
self.paddingView.layer.shadowRadius = 5
self.paddingView.layer.shadowOpacity = 0.5

---

全部回答都很好，但我想再补充一点

如果您在有表格单元格时遇到问题，Deque 一个新单元格存在阴影不匹配，因此在这种情况下，您需要将阴影代码放在 layoutSubviews 方法中，以便它在所有条件下都能正常运行。

-(void)layoutSubviews{
    [super layoutSubviews];

    [self.contentView setNeedsLayout];
    [self.contentView layoutIfNeeded];
    [VPShadow applyShadowView:self];
}

或在特定视图的 ViewControllers 中将阴影代码放在以下方法中，以便它运行良好

-(void)viewDidLayoutSubviews{
    [super viewDidLayoutSubviews];

    [self.viewShadow layoutIfNeeded];
    [VPShadow applyShadowView:self.viewShadow];
}

我已经为新开发者修改了我的影子实现，以获得更通用的形式，例如：

/*!
 @brief Add shadow to a view.

 @param layer CALayer of the view.

 */
+(void)applyShadowOnView:(CALayer *)layer OffsetX:(CGFloat)x OffsetY:(CGFloat)y blur:(CGFloat)radius opacity:(CGFloat)alpha RoundingCorners:(CGFloat)cornerRadius{
    UIBezierPath *shadowPath = [UIBezierPath bezierPathWithRoundedRect:layer.bounds cornerRadius:cornerRadius];
    layer.masksToBounds = NO;
    layer.shadowColor = [UIColor blackColor].CGColor;
    layer.shadowOffset = CGSizeMake(x,y);// shadow x and y
    layer.shadowOpacity = alpha;
    layer.shadowRadius = radius;// blur effect
    layer.shadowPath = shadowPath.CGPath;
}

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对于 Xamarian 同胞，答案的 Xamarin.iOS/C# 版本如下所示：

public override void DrawRect(CGRect area, UIViewPrintFormatter formatter)
{
    CGContext currentContext = UIGraphics.GetCurrentContext();
    currentContext.SaveState();
    currentContext.SetShadow(new CGSize(-15, 20), 5);
    base.DrawRect(area, formatter);
    currentContext.RestoreState();                
}

主要区别在于您获得了一个 CGContext 的实例，您可以在该实例上直接调用适当的方法。

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您可以使用此 Extension 添加阴影

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
    }
}

你可以这样称呼它

your_Custom_View.addShadow(offset: CGSize(width: 0, height: 1), color: UIColor.black, radius: 2.0, opacity: 1.0)

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