最近项目测试出一个隐藏已久的bug，经过多番测试，发现在iOS9下自定义的一个UICollectionViewCell只走一次awakeFromNib。

　　具体情况是，项目中有一个控制器用到了自定义的UICollectionView，有四组数据，然而有三组自定义的UICollectionViewCell布局和子控件是一样的，所以只注册了两种类型的cell

#import 
     
      @interface YimaiDoctorGroupMoreTopicCollectionView : UICollectionView+ (instancetype)collectionViewWithObject:(id)object;@end
     

#define kCollectionviewHeight 96.0#define kCommonIdentifier @"YimaiDoctorGroupMoreTopicCommonCollectionCell"#define kMyIdentifier @"YimaiDoctorGroupMoreTopicMyCollectionCell"#import "YimaiDoctorGroupMoreTopicCollectionView.h"@implementation YimaiDoctorGroupMoreTopicCollectionViewstatic NSString const *commonIdentifier = @"YimaiDoctorGroupMoreTopicCommonCollectionCell";static NSString const *myIdentifier = @"YimaiDoctorGroupMoreTopicMyCollectionCell";+ (instancetype)collectionViewWithObject:(id)object{    //流水布局    UICollectionViewFlowLayout *layout = [[UICollectionViewFlowLayout alloc] init];    layout.scrollDirection = UICollectionViewScrollDirectionHorizontal;    CGFloat itemHeight = kScreenH - kCollectionviewHeight - kNavigtaionHeight;    layout.itemSize = CGSizeMake(kScreenW, itemHeight);    layout.minimumLineSpacing = 0;    layout.minimumInteritemSpacing = 0;            //初始化    YimaiDoctorGroupMoreTopicCollectionView *collection = [[YimaiDoctorGroupMoreTopicCollectionView alloc] initWithFrame:CGRectZero collectionViewLayout:layout];    //注册　　 [collection registerNib:[UINib nibWithNibName:kCommonIdentifier bundle:nil] forCellWithReuseIdentifier:kCommonIdentifier];    [collection registerNib:[UINib nibWithNibName:kMyIdentifier bundle:nil] forCellWithReuseIdentifier:kMyIdentifier];    //分页    collection.pagingEnabled = YES;    //数据源，代理    collection.delegate = object;    collection.dataSource = object;    //    collection.backgroundColor = [UIColor clearColor];    return collection;}@end

在所属控制器的数据源方法中，初始化和赋值

#pragma mark - UICollectionViewDelegate- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section{    return 4;}- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath{    static NSString *identifier;    if (indexPath.item < 3) {        identifier = @"YimaiDoctorGroupMoreTopicCommonCollectionCell";        YimaiDoctorGroupMoreTopicCommonCollectionCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:identifier forIndexPath:indexPath];        cell.type = [NSString stringWithFormat:@"%ld",indexPath.item + 1];        FLOG(@"cell ======== %@", cell);        return cell;    }else{        identifier = @"YimaiDoctorGroupMoreTopicMyCollectionCell";        YimaiDoctorGroupMoreTopicMyCollectionCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:identifier forIndexPath:indexPath];        cell.type = (int)indexPath.item + 1;        return cell;    }}

每个自定义的UICollectionViewCell里面添加了UITableView作为子控件，并且能上拉加载，下拉刷新，所以有一些初始化

#pragma mark - life cycle- (void)awakeFromNib {    [super awakeFromNib];    //设置tableview    [self setTableViewAttributes];    self.page = 1;}

当前控制器里顶部还加了资格按钮，用来点击可以实现UICollectionView的滑动

上面是核心源码，看似很正确的实现，最后却验证在iOS9下“不能滑动”，即看似下面这句话不执行

[self.collectionView setContentOffset:CGPointMake(index * kScreenW, 0) animated:NO];

最后通过各种系统版本机型的调试，验证了，上面的这句setContentOffset没有问题，有问题的是，iOS9上YimaiDoctorGroupMoreTopicCommonCollectionCell的awakeFromNib方法只执行了一次，而在其他的手机版本下走了三次，所以导致当初注册的两种类型的cell，这里三种看似相同的cell现在都是完全一样了，数据都一样。类似于是用的同一个地址，而不是我们认为的，三种长得一样的cell都拥有自己独立的地址，所以才导致看着是没滑动，具体为什么还在不同的系统版本上有这种情况，查了资料也没什么头绪，有了解的伙伴们还请多多指点！！最后只附上解决方法：三种看似相同的cell不复用了，于是有了下面重用标识符的修改

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath{    static NSString *identifier;    if (indexPath.item < 3) {        identifier = [NSString stringWithFormat:@"%@-%ld",@"YimaiDoctorGroupMoreTopicCommonCollectionCell", indexPath.item];        YimaiDoctorGroupMoreTopicCommonCollectionCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:identifier forIndexPath:indexPath];        cell.type = [NSString stringWithFormat:@"%ld",indexPath.item + 1];        FLOG(@"cell ======== %@", cell);        return cell;    }else{        identifier = @"YimaiDoctorGroupMoreTopicMyCollectionCell";        YimaiDoctorGroupMoreTopicMyCollectionCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:identifier forIndexPath:indexPath];        cell.type = (int)indexPath.item + 1;        return cell;    }}

+ (instancetype)collectionViewWithObject:(id)object{    //流水布局    UICollectionViewFlowLayout *layout = [[UICollectionViewFlowLayout alloc] init];    layout.scrollDirection = UICollectionViewScrollDirectionHorizontal;    CGFloat itemHeight = kScreenH - kCollectionviewHeight - kNavigtaionHeight;    layout.itemSize = CGSizeMake(kScreenW, itemHeight);    layout.minimumLineSpacing = 0;    layout.minimumInteritemSpacing = 0;            //初始化    YimaiDoctorGroupMoreTopicCollectionView *collection = [[YimaiDoctorGroupMoreTopicCollectionView alloc] initWithFrame:CGRectZero collectionViewLayout:layout];    //注册    //解决ios9下 自定义的一个UICollectionViewCell只走一次awakeFromNib    for (int i = 0; i < 3; i++) {        [collection registerNib:[UINib nibWithNibName:kCommonIdentifier bundle:nil] forCellWithReuseIdentifier:[NSString stringWithFormat:@"%@-%d", @"YimaiDoctorGroupMoreTopicCommonCollectionCell", i]];    }//    [collection registerNib:[UINib nibWithNibName:kCommonIdentifier bundle:nil] forCellWithReuseIdentifier:kCommonIdentifier];    [collection registerNib:[UINib nibWithNibName:kMyIdentifier bundle:nil] forCellWithReuseIdentifier:kMyIdentifier];    //分页    collection.pagingEnabled = YES;    //数据源，代理    collection.delegate = object;    collection.dataSource = object;    //    collection.backgroundColor = [UIColor clearColor];    return collection;}