CenterAlignedLabel

CenterAlignedLabel.swift

//
//  CenterAlignedTextView.swift
//  Created by Rajin on 11/06/2019.
//

import Foundation
import UIKit
/**
 * Vertical center alignment label.
 * In sketch, text alignment center exists while iOS/Android does not.
 * To support this, CenterAlignedLabel moves drawRect of text rendering.
 * Note that text alignment property is not shown in Zeplin at the moment of 2019.6.12.
 */
class CenterAlignedLabel: UILabel {

    override init(frame: CGRect) {
        super.init(frame: frame)
    }

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

    override func drawText(in rect: CGRect) {
        // offset by font
        // Logic of vertical center align in sketch is
        // capHeight to be the vertical center of the label.

        // Graphical explanation
        // |---|-------------|-----------|
        // |-----------------|             : ascender
        //                   |-----------| : descender
        //     |-------------|             : capHeight
        let topCapPad = font.ascender - font.capHeight
        let bottomCapPad = -font.descender
        let fontOffset = (bottomCapPad - topCapPad) / 2

        let offsetY = fontOffset
        super.drawText(in: rect.offsetBy(dx: 0, dy: offsetY))
    }
}