swift 自定义一个可设置 text 的垂直位置的 Label

import UIKit

enum VerticalAlignment
{
case VerticalAlignmentTop//default
case VerticalAlignmentMiddle
case VerticalAlignmentBottom
}

class VerticalLabel: UILabel
{
var verticalAlignment: VerticalAlignment = .VerticalAlignmentTop {
didSet {
self.setNeedsDisplay()
}
}

override init(frame: CGRect) {
super.init(frame: frame)
self.verticalAlignment = VerticalAlignment.VerticalAlignmentTop
}

required init(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)!
}

override func textRect(forBounds bounds: CGRect, limitedToNumberOfLines numberOfLines: Int) -> CGRect {
var superRect:CGRect = super.textRect(forBounds: bounds, limitedToNumberOfLines: numberOfLines)
switch self.verticalAlignment {
case VerticalAlignment.VerticalAlignmentTop:
superRect.origin.y = bounds.origin.y
case VerticalAlignment.VerticalAlignmentBottom:
superRect.origin.y = bounds.origin.y + bounds.size.height  - superRect.size.height
case VerticalAlignment.VerticalAlignmentMiddle:
superRect.origin.y = bounds.origin.y + (bounds.size.height - superRect.size.height) / 2
}
return superRect
}
override func drawText(in rect: CGRect) {
let rect:CGRect = self.textRect(forBounds: rect, limitedToNumberOfLines: self.numberOfLines)
super.drawText(in: rect)
}

}