异常信息,请大家分析下,主要是什么原因,谢谢.(有时候会挂机)

*** Terminating app due to uncaught exception 'NSGenericException', reason: '*** Collection <CALayerArray: 0xf87a260> was mutated while being enumerated.(
    "<CALayer: 0xf897510>",
    "<CALayer: 0xf87a310>",
    "<CALayer: 0xf8942e0>",
    "<CALayer: 0xf8951d0>",
    "<CALayer: 0xf895270>",
    "<CALayer: 0xf8974e0>",
    "<CALayer: 0xf8a2ee0>",
    "<CALayer: 0xf8a2f10>",
    "<CALayer: 0x60acae0>"
)'
*** Call stack at first throw:
(
0   CoreFoundation                      0x01bf2be9 __exceptionPreprocess + 185
1   libobjc.A.dylib                     0x01d475c2 objc_exception_throw + 47
2   CoreFoundation                      0x01bf26a9 __NSFastEnumerationMutationHandler + 377
3   UIKit                               0x008059a0 -[UIView(Hierarchy) _makeSubtreePerformSelector:withObject:withObject:copySublayers:] + 239
4   UIKit                               0x00805a5c -[UIView(Hierarchy) _makeSubtreePerformSelector:withObject:withObject:copySublayers:] + 427
5   UIKit                               0x00805a5c -[UIView(Hierarchy) _makeSubtreePerformSelector:withObject:withObject:copySublayers:] + 427
6   UIKit                               0x00805a5c -[UIView(Hierarchy) _makeSubtreePerformSelector:withObject:withObject:copySublayers:] + 427
7   UIKit                               0x007fab0c -[UIView(Hierarchy) _makeSubtreePerformSelector:withObject:] + 64
8   UIKit                               0x007fcb9e -[UIView(Internal) _addSubview:positioned:relativeTo:] + 474
9   UIKit                               0x007fb2ac -[UIView(Hierarchy) insertSubview:atIndex:] + 64
10  UIKit                               0x008399fc -[UITableView(_UITableViewPrivate) _addContentSubview:atBack:] + 101
11  UIKit                               0x0083fccb -[UITableView(UITableViewInternal) _createPreparedCellForGlobalRow:withIndexPath:] + 1867
12  UIKit                               0x0083577f -[UITableView(UITableViewInternal) _createPreparedCellForGlobalRow:] + 75
13  UIKit                               0x0084a450 -[UITableView(_UITableViewPrivate) _updateVisibleCellsNow:] + 1561
14  UIKit                               0x00842538 -[UITableView layoutSubviews] + 242
15  QuartzCore                          0x0160d451 -[CALayer layoutSublayers] + 181
16  QuartzCore                          0x0160d17c CALayerLayoutIfNeeded + 220
17  QuartzCore                          0x0160637c _ZN2CA7Context18commit_transactionEPNS_11TransactionE + 310
18  QuartzCore                          0x016060d0 _ZN2CA11Transaction6commitEv + 292
19  QuartzCore                          0x016367d5 _ZN2CA11Transaction17observer_callbackEP19__CFRunLoopObservermPv + 99
20  CoreFoundation                      0x01bd3fbb __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__ + 27
21  CoreFoundation                      0x01b690e7 __CFRunLoopDoObservers + 295
22  CoreFoundation                      0x01b31bd7 __CFRunLoopRun + 1575
23  CoreFoundation                      0x01b31240 CFRunLoopRunSpecific + 208
24  CoreFoundation                      0x01b31161 CFRunLoopRunInMode + 97
25  GraphicsServices                    0x02267268 GSEventRunModal + 217
26  GraphicsServices                    0x0226732d GSEventRun + 115
27  UIKit                               0x007da42e UIApplicationMain + 1160
28  Áà±ËÅä                              0x00001ed8 main + 102
29  Áà±ËÅä                              0x00001e69 start + 53
)
terminate called after throwing an instance of 'NSException'