ios - 如何为透明的 UIView 添加阴影？

Question

我怎样才能重现这种阴影？我的问题，如果我使用高 alpha 颜色或 clearColor，没有阴影，如果我使用低 alpha 颜色，我看不到板下的阴影。随着音量的变化（彩色部分），阴影也在移动，所以它不是纯 Photoshop。

Answer 1

尝试使用您的视图的这些属性。它可能最终会得到一些东西

    view.layer.shadowColor = [UIColor colorWithWhite:.5 alpha:1].CGColor;
    view.layer.shadowRadius = 4.0f;
    view.layer.shadowPath = CGPathCreateWithRect(CGRectMake(0, 0, 50, 50), NULL);
    view.layer.shadowOpacity = 1.0f;
    view.layer.shadowOffset = CGSizeMake(1, 1);

顺便说一句，如果 CGPathRelease(rect) 最后很抱歉，它会泄漏。

Answer 2

在搜索并没有找到这个问题的答案后，我在 Swift 5 中编写了以下扩展：

extension UIView {
    func makeClearViewWithShadow(
        cornderRadius: CGFloat,
        shadowColor: CGColor,
        shadowOpacity: Float,
        shadowRadius: CGFloat) {

        self.frame = self.frame.insetBy(dx: -shadowRadius * 2,
                                        dy: -shadowRadius * 2)
        self.backgroundColor = .clear
        let shadowView = UIView(frame: CGRect(
            x: shadowRadius * 2,
            y: shadowRadius * 2,
            width: self.frame.width - shadowRadius * 4,
            height: self.frame.height - shadowRadius * 4))
        shadowView.backgroundColor = .black
        shadowView.layer.cornerRadius = cornderRadius
        shadowView.layer.borderWidth = 1.0
        shadowView.layer.borderColor = UIColor.clear.cgColor

        shadowView.layer.shadowColor = shadowColor
        shadowView.layer.shadowOpacity = shadowOpacity
        shadowView.layer.shadowRadius = shadowRadius
        shadowView.layer.masksToBounds = false
        self.addSubview(shadowView)

        let p:CGMutablePath = CGMutablePath()
        p.addRect(self.bounds)
        p.addPath(UIBezierPath(roundedRect: shadowView.frame, cornerRadius: shadowView.layer.cornerRadius).cgPath)

        let s = CAShapeLayer()
        s.path = p
        s.fillRule = CAShapeLayerFillRule.evenOdd

       self.layer.mask = s
    }
}

使用示例：

myView.makeClearViewWithShadow(cornderRadius: 20, shadowColor: UIColor.black.cgColor, shadowOpacity: 0.5, shadowRadius: 30)

Answer 3

您将有两个图像，一个是彩色图像，另一个是它的阴影，阴影会随着彩色部分的扩展而扩大并增加宽度

没有本地方法可以做你所要求的，

Answer 4

我使用 UIImageView 来提供阴影。我创建了一个 1 像素宽、12 像素高的图像。图像是黑色的，但 alpha 是从顶部的 0.5 到底部的 0.0 的渐变，例如。RGBA 1.0,1.0,1.0,0.5 -> 1.0,1.0,1.0,0.0 - 然后我将 UIImageView 放在需要阴影的视图下方，并将其水平拉伸到视图的宽度上。当我需要在下面的滚动视图滚动时通过更改 UIImageView.alpha 值来更改阴影的强度时，我也使用了它

Answer 5

我的解决方案是继承 UIView。即使视图被调整大小，它也可以工作。

import UIKit

class ShadowOutsideView: UIView {
  let color: CGColor
  let opacity: Float
  let radius: CGFloat
  let offset: CGSize
  let shadowView = UIView()
  
  init(
    color: CGColor,
    opacity: Float,
    radius: CGFloat,
    offset: CGSize
  ) {
    self.color = color
    self.opacity = opacity
    self.radius = radius
    self.offset = offset
    super.init(frame: CGRect.zero)
    shadowView.frame = bounds
    shadowView.backgroundColor = .black
    shadowView.layer.shadowColor = color
    shadowView.layer.shadowOpacity = opacity
    shadowView.layer.shadowRadius = radius
    shadowView.layer.shadowOffset = offset
    shadowView.layer.masksToBounds = false
    self.addSubview(shadowView)
    
  }
  
  override func layoutSubviews() {
    shadowView.frame = bounds
    let inset = -(max(abs(offset.width), abs(offset.height))+radius) - 10 
    // - 10, had to put 10px extra otherwise it would cut shadow
    let maskFrame = bounds.inset(by: UIEdgeInsets(top: inset, left: inset, bottom: inset, right: inset))
    let p = CGMutablePath()
    p.addRect(maskFrame)
    p.addRect(bounds)
    let s = CAShapeLayer()
    s.path = p
    s.fillRule = .evenOdd
    shadowView.layer.mask = s
  }
}