在UITextView for iPhone上绘制格线

import UIKit

class LineTextView: UITextView {
    override func draw(_ rect: CGRect) {
        super.draw(rect)
        
        // 调用父类的drawRect方法，确保原有的文本绘制功能不受影响
        super.drawRect(rect)
        
        // 设置线条颜色
        UIColor.lightGray.setStroke()
        
        // 创建线条路径
        let path = UIBezierPath()
        
        // 获取每行文本的高度
        let lineHeight = self.font!.lineHeight
        
        // 获取文本内容
        let text = self.text as NSString
        
        // 获取每行文本的范围
        let range = text.paragraphRange(for: self.selectedRange)
        
        // 获取每行文本的起始位置和行数
        text.enumerateSubstrings(in: range, options: .byLines) { (substring, substringRange, _, _) in
            let lineRect = self.layoutManager.lineFragmentRect(forGlyphAt: substringRange.location, effectiveRange: nil)
            
            // 创建线条路径
            path.move(to: CGPoint(x: lineRect.origin.x, y: lineRect.origin.y + lineHeight))
            path.addLine(to: CGPoint(x: lineRect.origin.x + lineRect.size.width, y: lineRect.origin.y + lineHeight))
        }
        
        // 绘制线条
        path.stroke()
    }
}