自定义控制迅速崩溃

Question

这是我的自定义页面控件类。我在主故事板上创建了一个UIView，并给它一个类myPageControl。但它出于某种原因崩溃了。我不知道为什么。

import UIKit

class myPageControl: UIControl {

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
    }


    let kSmallCircleSize: CGSize = CGSize(width: 15.0, height: 15.0)
    let kBigCircleSize: CGSize = CGSize(width: 50.0, height: 50.0)
    let kSmallCirclesPadding: CGFloat = 35.0

    var numberOfPages: Int = 0
    var currentPage: Int = 0
    var layers: NSArray = []


    func incrementCurrentPage() {
        if self.currentPage < (self.numberOfPages - 1) {
            ++self.currentPage
        }
    }

    func decrementCurrentPage() {
        if self.currentPage > 0 {
            --self.currentPage
        }
    }

    func setNumberOfPagess(value: Int) {
        if numberOfPages != value {
            self.layers.forEach { $0.removeFromSuperlayer() }
            //self.layers.makeObjectsPerformSelector("removeFromSuperlayer")
            self.numberOfPages = value
            let numberOfPages: Int = self.numberOfPages
            var layers: [AnyObject] = [AnyObject](arrayLiteral: numberOfPages)
            var layer: CALayer = self.layer
            for var index = 0; index < numberOfPages; ++index {
                var shapeLayer: PageControlShapeLayer = PageControlShapeLayer()
                shapeLayer.path = UIBezierPath(ovalInRect: CGRectMake(0.0, 0.0, 10.0, 10.0)).CGPath
                shapeLayer.fillColor = UIColor.clearColor().CGColor
                shapeLayer.strokeColor = UIColor.blueColor().CGColor
                layers.append(shapeLayer)
                layer.addSublayer(shapeLayer)
            }
            self.layers = layers
        }
    }

    func setCurrentPages(value: Int) {
        if currentPage != value {
            self.currentPage = value
            self.setNeedsLayout()
        }
    }

    override func layoutSubviews() {
        let bounds: CGRect = self.bounds
        let midY: CGFloat = CGRectGetMidY(bounds)
        let midX: CGFloat = CGRectGetMidX(bounds)
        var layers: NSArray = self.layers
        let currentPage: Int = self.currentPage
        for var index = (currentPage - 1); index >= 0; --index {
            var shapeLayer: CAShapeLayer = layers[index] as! CAShapeLayer
            var rect: CGRect = CGRectMake((midX - (kBigCircleSize.width / 2.0) - (kSmallCirclesPadding * CGFloat(currentPage - index))), (midY - (kSmallCircleSize.height / 2.0)), kSmallCircleSize.width, kSmallCircleSize.height)
            shapeLayer.path = UIBezierPath(ovalInRect: rect).CGPath
        }

        var shapeLayer: CAShapeLayer = layers[currentPage] as! CAShapeLayer
        shapeLayer.path = UIBezierPath(ovalInRect: CGRectMake((midX - (kBigCircleSize.width / 2.0)), (midY - (kBigCircleSize.height / 2.0)), kBigCircleSize.width, kBigCircleSize.height)).CGPath
        for var index = (currentPage + 1); index < self.numberOfPages; ++index {
            var shapeLayer: CAShapeLayer = layers[index] as! CAShapeLayer
            var rectWidth = midX + kBigCircleSize.width / 2.0
            var rectWidth2 = kSmallCirclesPadding * CGFloat(index - currentPage) - kSmallCircleSize.width
            var rect: CGRect = CGRectMake((rectWidth + rectWidth2), (midY - (kSmallCircleSize.height / 2.0)), kSmallCircleSize.width, kSmallCircleSize.height)
            shapeLayer.path = UIBezierPath(ovalInRect: rect).CGPath
        }

    }

    override func touchesEnded(touches: Set<UITouch>, withEvent event: UIEvent?) {
        var touch: UITouch = touches.first!
        if touch.tapCount == 1 {
            let midX: CGFloat = CGRectGetMidX(self.bounds)
            if touch.locationInView(self).x < (midX - (kBigCircleSize.width / 2.0)) {
                self.decrementCurrentPage()
            }
            else if touch.locationInView(self).x > (midX + (kBigCircleSize.width / 2.0)) {
                self.incrementCurrentPage()
            }
        }
    }


}

当我运行此代码时，它会崩溃并给我以下内容：

2016-01-10 12:38:15.831 PageControl[22444:830608] *** Terminating app due to uncaught exception 'NSRangeException', reason: '*** -[__NSArray0 objectAtIndex:]: index 0 beyond bounds for empty NSArray'
*** First throw call stack:
(
    0   CoreFoundation                      0x0027ea84 __exceptionPreprocess + 180
    1   libobjc.A.dylib                     0x0235fe02 objc_exception_throw + 50
    2   CoreFoundation                      0x00225390 __CFArrayGetTypeID_block_invoke + 0
    3   CoreFoundation                      0x001c37f8 -[NSArray objectAtIndexedSubscript:] + 40
    4   PageControl                         0x0008f1ae _TFC11PageControl13myPageControl14layoutSubviewsfS0_FT_T_ + 590
    5   PageControl                         0x0008fa32 _TToFC11PageControl13myPageControl14layoutSubviewsfS0_FT_T_ + 34
    6   UIKit                               0x00f70eb7 -[UIView(CALayerDelegate) layoutSublayersOfLayer:] + 813
    7   libobjc.A.dylib                     0x02374059 -[NSObject performSelector:withObject:] + 70
    8   QuartzCore                          0x00d7180a -[CALayer layoutSublayers] + 144
    9   QuartzCore                          0x00d654ee _ZN2CA5Layer16layout_if_neededEPNS_11TransactionE + 388
    10  QuartzCore                          0x00d65352 _ZN2CA5Layer28layout_and_display_if_neededEPNS_11TransactionE + 26
    11  QuartzCore                          0x00d57e8b _ZN2CA7Context18commit_transactionEPNS_11TransactionE + 317
    12  QuartzCore                          0x00d8be03 _ZN2CA11Transaction6commitEv + 561
    13  QuartzCore                          0x00d8c6c4 _ZN2CA11Transaction17observer_callbackEP19__CFRunLoopObservermPv + 92
    14  CoreFoundation                      0x0019861e __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__ + 30
    15  CoreFoundation                      0x0019857e __CFRunLoopDoObservers + 398
    16  CoreFoundation                      0x0018d728 CFRunLoopRunSpecific + 504
    17  CoreFoundation                      0x0018d51b CFRunLoopRunInMode + 123
    18  UIKit                               0x00ea1854 -[UIApplication _run] + 540
    19  UIKit                               0x00ea71eb UIApplicationMain + 160
    20  PageControl                         0x00091c6c main + 140
    21  libdyld.dylib                       0x02dcaa21 start + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException
(lldb)

有谁知道如何解决这个问题，我哪里出错？