swift3.0对绘图的API进行了优化，看起来更swift了。

看下UI的构造。设置画笔粗细、清空面板和保存到本地

下面直接看画板文件

这里我做的比较复杂，记录触摸到的每个点，再连成路径，其实直接用可变路径CGMutablePath可变路径就可以实现。

成员变量

    public var lineWidth:CGFloat = 1
    fileprivate var allLineArray = [[CGPoint]]()   //所有的线    记录每一条线
    fileprivate var currentPointArray = [CGPoint]() //当前画线的点  画完置空 增加到 线数组中
    fileprivate var allPointWidth = [CGFloat]()    //所有的线宽

设置触摸时间，开始时记录第一个点并重绘（不重绘就没有只画一个点得效果），移动时不断记录并重绘。

    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        let point:CGPoint = (event?.allTouches?.first?.location(in: self))!
        //路径起点
        currentPointArray.append(point)
        self.setNeedsDisplay()
    }

    override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
        let point:CGPoint = (event?.allTouches?.first?.location(in: self))!
        //路径
        currentPointArray.append(point)
        //刷新视图
        self.setNeedsDisplay()
    }

由于我们的点都是存在数组中，当要清空画板时 只要将数组清空就可以了

    func cleanAll(){
        allLineArray.removeAll()
        currentPointArray.removeAll()
        allPointWidth.removeAll()
        self.setNeedsDisplay()
    }

下面看下 重绘的主逻辑

 override func draw(_ rect: CGRect) {
        let context = UIGraphicsGetCurrentContext()
        context?.setLineCap(.round)
        context?.setLineJoin(.round)
 
        //绘制之前的线
        if allLineArray.count > 0 {
            //遍历之前的线
            for i in 0..<allLineArray.count {
                let tmpArr = allLineArray[i]
                if tmpArr.count > 0 {
                    //画线
                    context?.beginPath()
                    //取出起始点
                    let sPoint:CGPoint = tmpArr[0]
                    context?.move(to: sPoint)
                    //取出所有当前线的点
                    for j in 0..<tmpArr.count {
                        let endPoint:CGPoint = tmpArr[j]
                        context?.addLine(to: endPoint)
                    }
                    context?.setLineWidth(allPointWidth[i])
                    context?.strokePath()
                }
            }
        }
        
        if currentPointArray.count > 0 {
            //绘制当前线
            context?.beginPath()
            context?.setLineWidth(self.lineWidth)
            context?.move(to: currentPointArray[0])
            print(currentPointArray[0])

            for i in 0..<currentPointArray.count {
                context?.addLine(to: currentPointArray[i])
                print(currentPointArray[i])
            }
            context?.strokePath()  
        }
    }

保存成图片可很简单，只要截屏设置范围就行

    //保存图片
    @IBAction func savePic(_ sender: Any) {
        
        let height:CGFloat = self.view.bounds.size.height - self.saveBtn.frame.height - 10
        let imageSize :CGSize = CGSize(width: self.view.bounds.size.width, height: height)
        UIGraphicsBeginImageContext(imageSize)
        view.layer.render(in: UIGraphicsGetCurrentContext()!)
        let img:UIImage = UIGraphicsGetImageFromCurrentImageContext()!
        UIGraphicsEndImageContext()
        UIImageWriteToSavedPhotosAlbum(img, self, #selector(image(_:didFinishSavingWithError:contextInfo:)), nil)
    }
    
    //保存图片回调
    func image(_ image: UIImage, didFinishSavingWithError error: NSError?, contextInfo:UnsafeRawPointer) {
        var resultTitle:String?
        var resultMessage:String?
        if error != nil {
            resultTitle = "错误"
            resultMessage = "保存失败,请检查是否允许使用相册"
        } else {
            resultTitle = "提示"
            resultMessage = "保存成功"
        }
        let alert:UIAlertController = UIAlertController.init(title: resultTitle, message:resultMessage, preferredStyle: .alert)
        alert.addAction(UIAlertAction.init(title: "确定", style: .default, handler: nil))
        self.present(alert, animated: true, completion: nil)
    }

不过千万别忘了给app设置相册的权限

在info.plist中添加Privacy - Photo Library Usage Description属性即可，value值为提示信息

效果：

有兴趣的童靴可可以直接用可变路径实现下 逻辑更简单 完了。

https://github.com/gongxiaokai/paintViewDemo