My CoreGraphics code is working really slowly. How can I make this custom UIScrollView perform better?

Question

I made a custom class that creates a sort of timeline that is meant to be scrolled horizontally. Here's the code for my custom UIScrollView :

import UIKit

struct DataPoint {
    var fillColor: UIColor = UIColor.grayColor()

    init(color: UIColor) {
        fillColor = color
    }
}

@IBDesignable
class MyView: UIScrollView {

    @IBInspectable var lineColor: UIColor = UIColor.grayColor()
    @IBInspectable var lineHeight: CGFloat = 65
    @IBInspectable var lineWidth: CGFloat = 15
    @IBInspectable var lineGap: CGFloat = 25
    @IBInspectable var lineCount: Int = 0

    var dataPoints = [DataPoint(color: UIColor.greenColor()), DataPoint(color: UIColor.blueColor())]

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

    }

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        setupValues()
        //fatalError("init(coder:) has not been implemented")
    }

    func setupValues() {

        self.contentSize = CGSize(width: self.frame.width * 2, height: self.frame.height)

        self.backgroundColor = UIColor.whiteColor()
        self.lineCount = Int(self.frame.width / lineGap)
    }

    override internal func layoutSubviews() {
        super.layoutSubviews()
        self.setNeedsDisplay()
        self.layoutIfNeeded()
    }

    override func drawRect(rect: CGRect) {

        let ctx = UIGraphicsGetCurrentContext()
        CGContextSaveGState(ctx)

        for i in 0...lineCount {

            let start = CGPoint(x: CGFloat(i) * lineGap, y: self.frame.height)
            let end = CGPoint(x: CGFloat(i) * lineGap, y: self.frame.height - lineHeight)

            drawLine(from: start, to: end, color: UIColor.grayColor())

            if i % (lineCount / (dataPoints.count + 2)) == 0 && i != 0 && i != lineCount {
                drawPoint(at: end, radius: 5, color: UIColor.orangeColor())
            }
        }

        CGContextRestoreGState(ctx)
    }

    func drawLine(from start: CGPoint, to end: CGPoint, color: UIColor) {

        let path = UIBezierPath()
        path.moveToPoint(start)
        path.addLineToPoint(end)

        let shapeLayer = CAShapeLayer()
        shapeLayer.path = path.CGPath
        shapeLayer.strokeColor = color.CGColor
        shapeLayer.lineWidth = 1

        self.layer.addSublayer(shapeLayer)
    }

    func drawPoint(at center: CGPoint, radius: CGFloat, color: UIColor) {

        let path = UIBezierPath(arcCenter: center, radius: radius, startAngle: CGFloat(0), endAngle: CGFloat(M_PI * 2), clockwise: true)

        let shapeLayer = CAShapeLayer()
        shapeLayer.path = path.CGPath
        shapeLayer.fillColor = color.CGColor
        shapeLayer.strokeColor = UIColor.blackColor().CGColor
        shapeLayer.lineWidth = 0.5

        self.layer.addSublayer(shapeLayer)
    }
}

On my device and on the simulators, this is extremely slow and laggy. What exactly am I doing wrong here ? And what steps can I take to achieve a solid 60fps while scrolling ?

Answer 1

Hello I found your problem, your problem is

override internal func layoutSubviews() {
    super.layoutSubviews()
    self.setNeedsDisplay()
    self.layoutIfNeeded()
}

you are accidentally in a never-ending paint loop

replace this by this

override internal func layoutSubviews() {
    super.layoutSubviews()
}

or remove at all

I hope this Helps you, for me works great