在iOS中用TouchesMoved绘制CGContext线

import UIKit

class DrawingView: UIView {
    var lastPoint: CGPoint?
    
    override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
        guard let touch = touches.first else { return }
        
        let currentPoint = touch.location(in: self)
        
        if let lastPoint = lastPoint {
            drawLine(from: lastPoint, to: currentPoint)
        }
        
        lastPoint = currentPoint
    }
    
    func drawLine(from startPoint: CGPoint, to endPoint: CGPoint) {
        UIGraphicsBeginImageContextWithOptions(bounds.size, false, 0)
        guard let context = UIGraphicsGetCurrentContext() else { return }
        
        layer.render(in: context)
        
        context.move(to: startPoint)
        context.addLine(to: endPoint)
        context.setLineCap(.round)
        context.setLineWidth(5)
        context.setStrokeColor(UIColor.red.cgColor)
        context.strokePath()
        
        layer.contents = UIGraphicsGetImageFromCurrentImageContext()?.cgImage
        
        UIGraphicsEndImageContext()
    }
}