LineHeightLabel.swift

//
//  LineHeightLabel.swift
//  LineHeightLabel
//
//  Created by Shinichiro Oba on 20/06/2018.
//  Copyright © 2018 bricklife.com. All rights reserved.
//

import UIKit

class LineHeightLabel: UILabel {
    
    private var _lineHeight: CGFloat = 0.0
    var lineHeight: CGFloat {
        set {
            _lineHeight = newValue
            update()
        }
        get {
            return max(font.lineHeight, _lineHeight)
        }
    }
    
    override var text: String? { didSet { update() } }
    override var font: UIFont! { didSet { update() } }
    override var textColor: UIColor! { didSet { update() } }
    override var textAlignment: NSTextAlignment { didSet { update() } }
    
    private func update() {
        let paragraphStyle = NSMutableParagraphStyle()
        paragraphStyle.lineSpacing = lineHeight - font.lineHeight
        paragraphStyle.alignment = textAlignment
        
        var attr = [NSAttributedStringKey : Any]()
        attr[.font] = font
        attr[.foregroundColor] = textColor
        attr[.paragraphStyle] = paragraphStyle
        
        attributedText = text.flatMap { NSAttributedString(string: $0, attributes: attr) }
    }
    
    override var intrinsicContentSize: CGSize {
        var size = super.intrinsicContentSize
        
        let lineHeight = ceil(self.lineHeight * 2) / 2
        let numOflines = ceil(size.height / lineHeight)
        size.height = lineHeight * numOflines
        
        return size
    }
}