我是调试iOS异常的新手。
在fabric.io网站上，我可以看到一些用户看到了这次崩溃。 有人可以帮我开始吗？
Crashed: com.apple.main-thread
0 gismoapp 0x114760 specialized WeekPlanController.scrollViewWillBeginDragging(UIScrollView) -> () (WeekPlanController.swift:428)
1 gismoapp 0x1144a0 specialized WeekPlanController.scrollViewWillBeginDragging(UIScrollView) -> () (WeekPlanController.swift:428)
2 gismoapp 0x11102c @objc WeekPlanController.scrollViewWillBeginDragging(UIScrollView) -> () (WeekPlanController.swift)
3 UIKit 0x261b4609 -[UIScrollView(UIScrollViewInternal) _scrollViewWillBeginDragging] + 232
4 UIKit 0x261b3a9d -[UIScrollView _updatePanGesture] + 284
5 UIKit 0x265685db _UIGestureRecognizerSendTargetActions + 142
6 UIKit 0x261a08e3 _UIGestureRecognizerSendActions + 170
7 UIKit 0x26030d15 -[UIGestureRecognizer _updateGestureWithEvent:buttonEvent:] + 1004
8 UIKit 0x2656993f ___UIGestureRecognizerUpdate_block_invoke898 + 62
9 UIKit 0x25ff1587 _UIGestureRecognizerRemoveObjectsFromArrayAndApplyBlocks + 298
10 UIKit 0x25fedaf9 _UIGestureRecognizerUpdate + 2920
11 UIKit 0x2602ec01 -[UIWindow _sendGesturesForEvent:] + 904
12 UIKit 0x2602e3b3 -[UIWindow sendEvent:] + 622
13 UIKit 0x25ffec85 -[UIApplication sendEvent:] + 204
14 UIKit 0x25ffd229 _UIApplicationHandleEventQueue + 5016
15 CoreFoundation 0x219efa67 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 14
16 CoreFoundation 0x219ef657 __CFRunLoopDoSources0 + 454
17 CoreFoundation 0x219ed9bf __CFRunLoopRun + 806
18 CoreFoundation 0x2193c289 CFRunLoopRunSpecific + 516
19 CoreFoundation 0x2193c07d CFRunLoopRunInMode + 108
20 GraphicsServices 0x22f58af9 GSEventRunModal + 160
21 UIKit 0x260672c5 UIApplicationMain + 144
22 gismoapp 0xb7084 main (AppDelegate.swift:14)
23 libdispatch.dylib 0x215e8873 (Missing)
有问题的代码：
func scrollViewWillBeginDragging(scrollView: UIScrollView){
if let lastSyncDate = Settings.lastSyncedDate {
// This is line 428 in WeekPlanController
self.refreshControl.attributedTitle = NSAttributedString(string: "last synced \(lastSyncDate.relativeTimeToString()) ago")
}
}