Draw on large UIView take a lot of memory - ios

Question

when I start to draw on large UIView ( width: 3700 , height: 40000 ), it takes a lot of memory
when app starts, memory is 150 MB and when start drawing on it( calling setNeedsDisplay method) take around 1 GB and app is gonna crash
class DrawingVc: UIViewController {
let contentView = DrawableView()
override func viewDidLoad() {
super.viewDidLoad()
view.backgroundColor = .white
contentView.translatesAutoresizingMaskIntoConstraints = false
contentView.backgroundColor = .clear
self.view.addSubview(contentView)
contentView.frame = CGRect(x: 0, y: 0, width:view.frame.width, height:
view.frame.height * 50)
}
here is the code of custom view, as you can see, setNeedsDisplay runs on touchMoves
class DrawableView: UIView {
var mLastPath: UIBezierPath?
weak var scdelegate: DrawableViewDelegate?
var isDrawEnable = true
private var drawingLines : [UIBezierPath] = []
override init(frame: CGRect) {
super.init(frame: frame)
}
required public init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
}
override func draw(_ rect: CGRect) {
debugPrint("request draw")
drawLine()
}
private func drawLine() {
UIColor.blue.setStroke()
for line in drawingList {
line.lineWidth = 4
line.stroke()
line.lineCapStyle = .round
}
}
var drawingList = [UIBezierPath]()
override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
if touches.count == 2 {
return
}
let location = (touches.first?.location(in: self))!
mLastPath = UIBezierPath()
mLastPath?.move(to: location)
prevPoint = location
drawingList.append(mLastPath!)
}
var prevPoint: CGPoint?
var isFirst = true
override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
}
override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
debugPrint("touchesMoved: " , (touches.first?.location(in: self).x)! , (touches.first?.location(in: self).y)! )
if let coalescedtouches = event?.coalescedTouches(for: touches.first!)
{
for coalescedTouch in coalescedtouches
{
let locationInView = coalescedTouch.location(in: self)
if let prevPoint = prevPoint {
let midPoint = CGPoint( x: (locationInView.x + prevPoint.x) / 2, y: (locationInView.y + prevPoint.y) / 2)
if isFirst {
mLastPath?.addLine(to: midPoint)
}else {
mLastPath?.addQuadCurve(to: midPoint, controlPoint: prevPoint)
}
isFirst = false
} else {
mLastPath?.move(to: locationInView)
}
prevPoint = locationInView
}
}
setNeedsDisplay()
}
}
What makes this problem and how that fix?

Answer 1

Your view is larger than the largest possible screen on an iOS device, so I suppose your view is embedded in a scrollview. You should only draw the visible parts of your view. Unfortunately, this is not supported by UIView directly. You may take a look on CATiledLayer, which supports drawing of only visible parts of a layer, and it supports different levels of details for zoomed layers, too.