UIView.mask 设置颜色

Question

我有一个 50 像素的方形 UIView，我将它设置为我的超级视图的掩码。

let squareView = UIView(frame...)

self.view.mask = squareView

结果是一个 50px 的正方形透明区域，但它周围的遮罩区域的颜色始终为白色。如何将透明方块周围蒙版区域的颜色更改为黑色？

 _______________
|               |    
|    <-------------- Masked area that I would like to change the color of
|               |
|      000000   |
|      000000 <-------- squareView: becomes transparent as expected
|      000000   |
|      000000   |
|               |
|               |
|               |
|_______________|

Answer 1

我想，这是一个演示您想要的效果的代码片段。您应该能够将它粘贴到一个新的“单一视图”iOS 项目中，作为viewDidLoad()Xcode 模板创建的视图控制器的方法。

我需要一些方法来设置蒙版视图的内容而不创建子类UIView（因为我很懒），所以我的示例创建了一个图像（其 alpha 通道大部分为 1.0，具有 100x100 正方形的清晰 alpha 通道）。我将其设置为遮罩视图的内容。

最后的计时器只是循环显示外部视图的一堆颜色，因为...很有趣。

override func viewDidLoad() {
      super.viewDidLoad()
      self.view.backgroundColor = UIColor.blue

      let overallView = UIView(frame: CGRect(x:100, y:100, width:300, height:300))
      overallView.backgroundColor = UIColor.green

      // Draw a graphics with a mostly solid alpha channel
      // and a square of "clear" alpha in there.
      UIGraphicsBeginImageContext(overallView.bounds.size)
      let cgContext = UIGraphicsGetCurrentContext()
      cgContext?.setFillColor(UIColor.white.cgColor)
      cgContext?.fill(overallView.bounds)
      cgContext?.clear(CGRect(x:100, y:100, width: 100, height: 100))
      let maskImage = UIGraphicsGetImageFromCurrentImageContext()
      UIGraphicsEndImageContext()

      // Set the content of the mask view so that it uses our
      // alpha channel image
      let maskView = UIView(frame: overallView.bounds)
      maskView.layer.contents = maskImage?.cgImage
      overallView.mask = maskView

      self.view.addSubview(overallView)

      var hue = CGFloat(0)
      Timer.scheduledTimer(withTimeInterval: 0.2, repeats: true) {
          (_) in
          let color = UIColor(hue: hue, saturation: 1.0, brightness: 1.0, alpha: 1.0)
          hue = hue + (1.0/20);
          if hue >= 1.0 { hue = 0 }

          overallView.backgroundColor = color
      }
  }