iOS9下UICollectionViewCell的awakeFromNib問題

　　最近項目測試出一個隱藏已久的bug，經過多番測試，發現在iOS9下自定義的一個UICollectionViewCell只走一次awakeFromNib。

　　具體情況是，項目中有一個控制器用到了自定義的UICollectionView，有四組數據，然而有三組自定義的UICollectionViewCell佈局和子控制項是一樣的，所以只註冊了兩種類型的cell

#import <UIKit/UIKit.h>

@interface YimaiDoctorGroupMoreTopicCollectionView : UICollectionView

+ (instancetype)collectionViewWithObject:(id)object;

@end

#define kCollectionviewHeight 96.0
#define kCommonIdentifier @"YimaiDoctorGroupMoreTopicCommonCollectionCell"
#define kMyIdentifier @"YimaiDoctorGroupMoreTopicMyCollectionCell"
#import "YimaiDoctorGroupMoreTopicCollectionView.h"

@implementation YimaiDoctorGroupMoreTopicCollectionView
static NSString const *commonIdentifier = @"YimaiDoctorGroupMoreTopicCommonCollectionCell";
static NSString const *myIdentifier = @"YimaiDoctorGroupMoreTopicMyCollectionCell";

+ (instancetype)collectionViewWithObject:(id)object
{
    //流水佈局
    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];
    //註冊
　　 [collection registerNib:[UINib nibWithNibName:kCommonIdentifier bundle:nil] forCellWithReuseIdentifier:kCommonIdentifier];
    [collection registerNib:[UINib nibWithNibName:kMyIdentifier bundle:nil] forCellWithReuseIdentifier:kMyIdentifier];
    //分頁
    collection.pagingEnabled = YES;
    //數據源，代理
    collection.delegate = object;
    collection.dataSource = object;
    //
    collection.backgroundColor = [UIColor clearColor];
    return collection;
}

@end

在所屬控制器的數據源方法中，初始化和賦值

#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;
    }
}

每個自定義的UICollectionViewCell裡面添加了UITableView作為子控制項，並且能上拉載入，下拉刷新，所以有一些初始化

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

當前控制器里頂部還加了資格按鈕，用來點擊可以實現UICollectionView的滑動

上面是核心源碼，看似很正確的實現，最後卻驗證在iOS9下“不能滑動”，即看似下麵這句話不執行

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

最後通過各種系統版本機型的調試，驗證了，上面的這句setContentOffset沒有問題，有問題的是，iOS9上YimaiDoctorGroupMoreTopicCommonCollectionCell的awakeFromNib方法只執行了一次，而在其他的手機版本下走了三次，所以導致當初註冊的兩種類型的cell，這裡三種看似相同的cell現在都是完全一樣了，數據都一樣。類似於是用的同一個地址，而不是我們認為的，三種長得一樣的cell都擁有自己獨立的地址，所以才導致看著是沒滑動，具體為什麼還在不同的系統版本上有這種情況，查了資料也沒什麼頭緒，有瞭解的伙伴們還請多多指點！！最後只附上解決方法：三種看似相同的cell不復用了，於是有了下麵重用標識符的修改

- (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
{
    //流水佈局
    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];
    //註冊
    //解決ios9下 自定義的一個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];
    //分頁
    collection.pagingEnabled = YES;
    //數據源，代理
    collection.delegate = object;
    collection.dataSource = object;
    //
    collection.backgroundColor = [UIColor clearColor];
    return collection;
}