iOS UIKit框架默认只能通过UILable的textAlignment属性调整其水平方向上的布局，设置文字水平居左、居中和居右。不能对文字垂直方向上的布局做出直接调整，但是我们通过重写UILabel的textRectForBounds和drawTextInRect方法，能够很便捷的调整UILable的内容布局，实现居上、垂直居中和居下的效果。具体实现如下：

创建VerticalAlignment枚举

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enum VerticalAlignment {
	case Top
	case Middle
	case Bottom
}

重写UILabel

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class HLable: UILabel {
    
    override init(frame: CGRect) {
        self.verticalAlignment = .Middle
        super.init(frame: frame)
    }
    
    required init?(coder aDecoder: NSCoder) {
        self.verticalAlignment = .Middle
        super.init(coder: aDecoder)
    }
    
    var verticalAlignment: VerticalAlignment {
        didSet {
            self.setNeedsDisplay()
        }
    }
    
    override func textRectForBounds(bounds: CGRect, limitedToNumberOfLines numberOfLines: Int) -> CGRect {
        var textRect = super.textRectForBounds(bounds, limitedToNumberOfLines: numberOfLines)
        switch self.verticalAlignment {
        case .Top:
            textRect.origin.y = bounds.origin.y
        case .Bottom:
            textRect.origin.y = bounds.origin.y + bounds.size.height - textRect.size.height
        case .Middle:
            textRect.origin.y = bounds.origin.y + (bounds.size.height - textRect.size.height) / 2.0
        }
        return textRect
    }
    
    override func drawTextInRect(rect: CGRect) {
        let actualRect = self.textRectForBounds(rect, limitedToNumberOfLines: numberOfLines)
        super.drawTextInRect(actualRect)
    }
}

使用方法

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let label = HLabel()
label.verticalAlignment = .Top