Crashlytics给了我下面的堆栈跟踪。崩溃发生的不一致。发生在所有的iOS 9设备上，但非常罕见。无法找出问题的来源。没有发生在任何设备上，我已经尝试崩溃了过去3天。

Crashed: com.apple.main-thread
0  cherish                        0x10014ee18 specialized PersonalizeViewController.collectionView(UICollectionView, cellForItemAtIndexPath : NSIndexPath) -> UICollectionViewCell (PersonalizeViewController.swift:159)
1  cherish                        0x1001497f0 @objc PersonalizeViewController.collectionView(UICollectionView, cellForItemAtIndexPath : NSIndexPath) -> UICollectionViewCell (PersonalizeViewController.swift)
2  UIKit                          0x188aef3a8 <redacted> + 432
3  UIKit                          0x188311adc <redacted> + 4628
4  UIKit                          0x18830c808 <redacted> + 228
5  UIKit                          0x1882a81e4 <redacted> + 656
6  QuartzCore                     0x185c3a994 <redacted> + 148
7  QuartzCore                     0x185c355d0 <redacted> + 292
8  QuartzCore                     0x185c35490 <redacted> + 32
9  QuartzCore                     0x185c34ac0 <redacted> + 252
10 QuartzCore                     0x185c34820 <redacted> + 500
11 QuartzCore                     0x185c2dde4 <redacted> + 80
12 CoreFoundation                 0x183104728 <redacted> + 32
13 CoreFoundation                 0x1831024cc <redacted> + 372
14 CoreFoundation                 0x1831028fc <redacted> + 928
15 CoreFoundation                 0x18302cc50 CFRunLoopRunSpecific + 384
16 GraphicsServices               0x184914088 GSEventRunModal + 180
17 UIKit                          0x188316088 UIApplicationMain + 204
18 cherish                        0x100142a50 main (AppDelegate.swift:19)
19 libdispatch.dylib              0x182bca8b8 (Missing)

它崩溃的代码是：

func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {
        if collectionView.tag == 1 {
            (---crash line---) let cell = select_date_collection_view.dequeueReusableCellWithReuseIdentifier(PERSONALIZE_SELECT_DATE_COLLECTION_CELL_IDENTIFIER, forIndexPath: indexPath) as! SelectDateCollectionViewCell 
            // Some changes to cell objects
            return cell
        } else if collectionView.tag == 2 {
            let cell = select_time_collection_view.dequeueReusableCellWithReuseIdentifier(PERSONALIZE_SELECT_TIME_COLLECTION_CELL_IDENTIFIER, forIndexPath: indexPath) as! SelectTimeCollectionViewCell
            // Some changes to cell objects
            return cell
        } else if collectionView.tag == 3 {
            let cell = add_customization_collection_view.dequeueReusableCellWithReuseIdentifier(PERSONALIZE_ADD_CUSTOMIZATION_COLLECTION_CELL_IDENTIFIER, forIndexPath: indexPath) as! AddCustomizationCollectionViewCell
            // Some changes to cell objects
            return cell
        }

        let cell: UICollectionViewCell = UICollectionViewCell()
        return cell
    }

已初始化viewDidLoad（）中的所有集合视图

select_date_collection_view.registerNib(UINib(nibName: "SelectDateCollectionViewCell", bundle: nil), forCellWithReuseIdentifier: PERSONALIZE_SELECT_DATE_COLLECTION_CELL_IDENTIFIER)
        select_date_collection_view.tag = 1
        select_date_collection_view.dataSource = self
        select_date_collection_view.delegate = self
        select_date_collection_view.showsHorizontalScrollIndicator = false
        select_date_collection_view.showsVerticalScrollIndicator = false
        select_date_collection_view.reloadData()

        select_time_collection_view.registerNib(UINib(nibName: "SelectTimeCollectionViewCell", bundle: nil), forCellWithReuseIdentifier: PERSONALIZE_SELECT_TIME_COLLECTION_CELL_IDENTIFIER)
        select_time_collection_view.tag = 2
        select_time_collection_view.dataSource = self
        select_time_collection_view.delegate = self
        select_time_collection_view.showsHorizontalScrollIndicator = false
        select_time_collection_view.showsVerticalScrollIndicator = false
        hideSelectTimeView()

        add_customization_collection_view.registerNib(UINib(nibName: "AddCustomizationCollectionViewCell", bundle: nil), forCellWithReuseIdentifier: PERSONALIZE_ADD_CUSTOMIZATION_COLLECTION_CELL_IDENTIFIER)
        add_customization_collection_view.tag = 3
        add_customization_collection_view.dataSource = self
        add_customization_collection_view.delegate = self
        add_customization_collection_view.showsHorizontalScrollIndicator = false
        add_customization_collection_view.showsVerticalScrollIndicator = false
        hideCustomizationsView()

错误发生的不一致，这是一个主要的关注原因。因为我无法找出什么是错误的，从itunes或崩溃日志没有帮助。