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Katz
Asked: 2020-12-16 15:50:38 +0800 CST 2020-12-16 15:50:38 +0800 CST

When deleting layers from the View the application crashes

  • 772

I have a very simple application. Which draws lines when you touch the screen with two fingers, when they lift their fingers I want to erase the drawing, and when they draw again show new lines.

However, when I delete the lines the first time, the next press causes an error with no error message. I figure I'm doing something small wrong, but I can't figure it out. Here is my code:

var prevX: CGFloat!
var prevY: CGFloat!

var startX: CGFloat = 150
var startY : CGFloat = 450

var reset: Bool = true

override func viewDidLoad() {
    super.viewDidLoad()

    var pan = UIPanGestureRecognizer(target: self, action: "pan:")
    pan.cancelsTouchesInView = false
    pan.delegate = self
    self.view.addGestureRecognizer(pan)
}

func pan(recognizer:UIPanGestureRecognizer) {
    print(self.view.layer)
    var state = recognizer.state

    if (state == UIGestureRecognizerState.Ended) {
        reset = true
        var sublayers = self.view.layer.sublayers
        for layer in sublayers {
            layer.removeFromSuperlayer()
        }
    } else {
        var interval = recognizer.translationInView(self.view)
        if (reset) {
            reset = false
            prevX = CGFloat(startX + interval.x)
            prevY = CGFloat(startY + interval.y)
        }
        var newPointX = startX + interval.x
        var newPointY = startY + interval.y

        var path = UIBezierPath().bezierPathByReversingPath()
        path.moveToPoint(CGPoint(x: prevX, y: prevY))
        path.addLineToPoint(CGPoint(x:newPointX, y:newPointY))

        var shapeLayer = CAShapeLayer()
        shapeLayer.path = path.CGPath
        shapeLayer.strokeColor = UIColor.blueColor().CGColor
        shapeLayer.lineWidth = 1.0
        shapeLayer.fillColor = UIColor.clearColor().CGColor

        self.view.layer.addSublayer(shapeLayer)

        prevX = newPointX
        prevY = newPointY

    }
}

A little more information about the error

Thread 1: EXC_BAD_ACCESS code=1, address=0x499e....
     ___UIApplicationExtensionGetAccurateShareServicesExtensionForIdentifier_block_invoke_2
    0x18c00e3c0:  adrp   x8, 54568
    0x18c00e3c4:  ldr    x8, [x8, #2248]
    0x18c00e3c8:  ldr    x8, [x8]
    0x18c00e3cc:  ldr    x9, [sp, #56]
    0x18c00e3d0:  sub    x8, x8, x9
    0x18c00e3d4:  cbnz   x8, 0x18c00e3fc           ; UIApplicationMain + 1548
    0x18c00e3d8:  movz   w0, #0

I think it is this line that is causing the error.

        for layer in sublayers {
        layer.removeFromSuperlayer()
    }

because if I remove it the program works without any problem ( but it doesn't delete the lines )

ios

2 Answers

  1. Best Answer

    The problem is because you are modifying the size of the Array of layers directly. To fix it, add the following variable:

    var layers = [CALayer]()

    Then, every time you "paint" a line, save it in that variable:

    layers.append(shapeLayer)
self.view.layer.addSublayer(shapeLayer)

    And finally:

    if (state == UIGestureRecognizerState.Ended) {

      reset = true
      for l in layers {
          l.removeFromSuperlayer()
      }

}

    With this you will no longer have problems.

    • 2

  2. What you can do is create a subclass of CAShapeLayerand use that subclass. So when you go to delete the lines, you can do a pre-check like this:

    // supongamos que la subclase de llama MyShapeLayer
for layer in sublayers {
    if layer is MyShapeLayer {
        layer.removeFromSuperlayer()
    }
}

    This should work for you.

    • 0