参考原文链接

原文使用ObjC编码,我翻译为了Swift. 先看运行效果图

实现一个绘图板功能的view,可以使用CoreGraphics调用draw完成,缺点是在绘制的后面的时候每次都重绘制全部内容,非常没有必要. 另一个建议,使用CAShapeLayer纪录绘制的路径,而且CAShapeLayer是专门为绘制路径所优化的layer,当然更有效率. 同时最重要的一点,声明当前UIView实现的layerClass为CAShapeLayer.

使用专有图层可以完成相应的更近恰当的任务,这样会比直接使用CoreGraphics绘制更加的高效.

//
//  DrawingView.swift
//  layerDemo
//
//  Created by grath on 15/9/17.
//  Copyright © 2015年 stone. All rights reserved.
//

import UIKit

class DrawingView: UIView {
    var path = UIBezierPath()
    //
    init() {
        super.init(frame: CGRectZero)
        let shapeLayer = self.layer as! CAShapeLayer
        shapeLayer.lineWidth = 2.0
        shapeLayer.lineCap = kCALineCapRound
        shapeLayer.strokeColor = UIColor.redColor().CGColor
        shapeLayer.fillColor = UIColor.clearColor().CGColor
        shapeLayer.masksToBounds = true //裁减掉超出当前view的layer绘制
        shapeLayer.shadowOffset = CGSizeMake(2.0,4.0)
        shapeLayer.shadowRadius = 2.0
        shapeLayer.shadowColor = UIColor.purpleColor().CGColor
    }
    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
    }
    
    override class func layerClass() -> AnyClass {
        //指定返回的layer类型 默认返回CALayer类型
        return CAShapeLayer.classForCoder()
    }
    
    override func touchesBegan(touches: Set<UITouch>,withEvent event: UIEvent?) {
        let p = touches.first?.locationInView(self)
        path.moveToPoint(p!)
    }
    override func touchesMoved(touches: Set<UITouch>,withEvent event: UIEvent?) {
        let p = touches.first?.locationInView(self)
        path.addLineToPoint(p!) //增加绘制点
        let shapeLayer = self.layer as! CAShapeLayer
        //指定path 开始绘制
        shapeLayer.path = self.path.CGPath
    }
}

以上为实现代码.

使用方法如下:

func addDrawView() {
        let drawVw = DrawingView()
        drawVw.layer.borderWidth = 4.0
        drawVw.layer.borderColor  = UIColor.grayColor().CGColor
        drawVw.frame = CGRectInset(self.view.bounds,50,100)
        
        var atrans = CATransform3DIdentity
        atrans.m34 = -1/500.0
        atrans = CATransform3DRotate(atrans,CGFloat(M_PI_4),1,0)
        //drawVw.layer.transform = atrans
        
        view.addSubview(drawVw)
    }