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

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

Answer 2

It looks to me that you are drawing the same thing every time. Everything is static... So why not draw it all once into a graphics context and make a UIImage out of it to add to the background of the scrollview (or foreground, depending on anything else you are doing)?