如何在UIView下绘制阴影？

我正在尝试在Cocoa Touch中的UIView底部边缘下方绘制阴影。 我知道我应该使用CGContextSetShadow()来绘制阴影，可是Quartz 2D编程指南有点模糊：

1. 保存图形状态。
2. 调用函数CGContextSetShadow ，传递适当的值。
3. 执行要向其应用阴影的全部图形。
4. 恢复图形状态

我在UIView子类中尝试了如下方法：

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

..但这对我不起做用，我对（a）接下来要去哪里和（b）是否须要对UIView进行任何操做以使其工做感到有些UIView ？

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#1楼

相同的解决方案，只是提醒您：您能够直接在情节提要中定义阴影。

例如：

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#2楼

对于在这里尝试了全部答案后都没法正常工做的人（以我本身！），只需确保在“属性”检查器中未启用“ 剪辑子视图” ...

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#3楼

使用Interface Builder的简单干净的解决方案

在您的项目中添加一个名为UIView.swift的文件（或仅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
        }
    }
}

而后，它将在“界面构建器”中为“实用工具面板”>“属性检查器”中的每一个视图提供：

您如今能够轻松设置阴影。

笔记：
-仅在运行时，阴影不会出如今IB中。
-正如Mazen Kasser所说

对于未能经过此方法工做的人，请确保未启用剪辑子视图（ clipsToBounds ）

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#4楼

您能够尝试这个....您能够使用这些值。 shadowRadius指示模糊量。 shadowOffset指示阴影的位置。

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

传播实例

建立基本阴影

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Shadow示例

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#5楼

迅捷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
    }
}