ios - 阻止 CALayer 阴影影响 subview ？

Question

我有一个自定义的UIControl，我想让它有一个阴影，所以我在它的layer上设置了相关的属性。阴影会根据需要出现在 View 周围，但阴影也会出现在作为 subview 的 UILabel 的文本下方。你怎么阻止这个？我只想要外部 super View 周围的阴影。

...
init() {        
    label = UILabel()
    label.translatesAutoresizingMaskIntoConstraints = false
    self.translatesAutoresizingMaskIntoConstraints = false
    addSubview(label)

    self.layer.masksToBounds = false
    self.layer.shadowColor = UIColor.blackColor().CGColor
    self.layer.shadowOpacity = 1.0
    self.layer.shadowRadius = 2.0

    // Adding these lines trying to explicitly stop shadow on label...
    label.layer.shadowOpacity = 0
    label.layer.shadowColor = nil
    ...
}

Answer 1

当父 View 的 alpha 小于 1.0 或没有背景颜色(即设置为透明颜色)时会发生这种情况。在这种情况下，阴影会转化为 subview 。看我的回答here了解更多详情。

苹果 Docs证明这一点:

Figure A-7 shows several different versions of the same sample layer with a red shadow applied. The left and middle versions include a background color so the shadow appears only around the border of the layer. However, the version on the right does not include a background color. In this case, the shadow is applied to the layer’s content, border, and sublayers.