swift UIButton-图文排列

swift 里没有OC的分类概念，但可以用extension为类拓展方法。

下面的extension 为UIButton提供了四种样式：
图上文下，图下文上，图左文右（UIButton默认样式），图右文左。
可以通过space设置图文之间的间距

enum LayoutStyle: Int {
   case imageTop
   case imageLeft
   case imageBottom
   case imageRight
}

extension UIButton {
   
   func layoutButton(_ style: LayoutStyle, space: CGFloat) {
       
       guard let titleL = self.titleLabel, let imageV = self.imageView else {
           return
       }
       
       let imageWidth = imageV.frame.size.width
       let imageHeight = imageV.frame.size.height
       
       let labelWidth = titleL.frame.size.width
       let labelHeight = titleL.frame.size.height
       
       let imageX = imageV.frame.origin.x
       let labelX = titleL.frame.origin.x
       
       let margin = labelX - imageX - imageWidth
       
       var imageInsets = UIEdgeInsets.zero
       var labelInsets = UIEdgeInsets.zero
       
       /**
        *  titleEdgeInsets是title相对于其上下左右的inset
        *  如果只有title，那它上下左右都是相对于button的，image也是一样；
        *  如果同时有image和label，那这时候image的上左下是相对于button，右边是相对于label的；title的上右下是相对于button，左边是相对于image的。
        */
       switch style {
       case .imageTop:
           imageInsets = UIEdgeInsets(top: -0.5 * labelHeight, left: 0.5 * labelWidth + 0.5 * margin + imageX, bottom: 0.5 * (labelHeight + space), right: 0.5 * (labelWidth - margin))
           labelInsets = UIEdgeInsets(top: 0.5 * (imageHeight + space), left: -(imageWidth - 5), bottom: -0.5 * imageHeight, right: 5)
           
       case .imageBottom:
           imageInsets = UIEdgeInsets(top: 0.5 * (labelHeight + space), left: 0.5 * labelWidth + imageX, bottom: -0.5 * labelHeight, right: 0.5 * labelWidth)
           labelInsets = UIEdgeInsets(top: -0.5 * imageHeight, left: -(imageWidth - 5), bottom:0.5 * (imageHeight + space), right: 5)
           
       case .imageRight:
           imageInsets = UIEdgeInsets(top: 0, left: 0.5 * (labelWidth + space), bottom: 0, right: -(labelWidth + 0.5 * space))
           labelInsets = UIEdgeInsets(top: 0, left: -(imageWidth + 0.5 * space), bottom: 0, right: imageWidth + space * 0.5)
           
       default:
           imageInsets = UIEdgeInsets(top: 0, left: 0, bottom: 0, right: 0.5 * space)
           labelInsets = UIEdgeInsets(top: 0, left: 0.5 * space, bottom: 0, right: 0)
       }
       
       self.titleEdgeInsets = labelInsets;
       self.imageEdgeInsets = imageInsets;
   }
   
}