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错误的完整提示代码:

2016-08-31 16:13:34.189 xxxx[1424:25534] *** Assertion failure in -[UICollectionView _createPreparedSupplementaryViewForElementOfKind:atIndexPath:withLayoutAttributes:applyAttributes:], /BuildRoot/Library/Caches/com.apple.xbs/Sources/UIKit_Sim/UIKit-3512.60.7/UICollectionView.m:1599

2016-08-31 16:13:34.278 xxxx[1424:25534] *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'UICollectionView dataSource is not set'

出现这个错误的情况是我设置了collectionView中每个section的header

而且错误并不是想错误描述的UICollectionView dataSource is not set没有设置数据源

先说说如何设置collectionView的header

3个文件需要写代码, HeaderView.h(设置header时用的view), HeaderView.m, ViewController.m

直接上代码

HeaderView.h

#import 
   
    @interface HeaderView : UICollectionReusableView@property(nonatomic, strong)UILabel *titleLabel;@end
   

HeaderView.m

#import "HeaderView.h"@implementation HeaderView- (instancetype)initWithFrame:(CGRect)frame{    self = [super initWithFrame:frame];    if (self)    {        _titleLabel = [[UILabel alloc] init];        _titleLabel.text = @"这里是section的header";        _titleLabel.backgroundColor = [UIColor greenColor];        [self addSubview:_titleLabel];    }    return self;}- (void)layoutSubviews{    [super layoutSubviews];    _titleLabel.frame = CGRectMake(0, 0, self.frame.size.width, self.frame.size.height);}    @end

ViewController.m

#import "ViewController.h"#import "HeaderView.h"@interface ViewController ()
   
    @property(nonatomic, strong)UICollectionView *collectionView;@end@implementation ViewController- (void)loadView{    [super loadView];        UICollectionViewFlowLayout *flowLayout = [[UICollectionViewFlowLayout alloc] init];    flowLayout.itemSize = CGSizeMake(80, 30);    flowLayout.minimumLineSpacing = 10;    flowLayout.minimumInteritemSpacing = 10;    flowLayout.sectionInset = UIEdgeInsetsMake(10, 10, 10, 10);        // 注意这句话: 当collectionView不是根视图的时候, 存在返回按钮, 返回前一页, 此时设置header的尺寸这样写返回前一页后会crash, 要用代理方法设置高度//    [flowLayout setHeaderReferenceSize:CGSizeMake(self.view.frame.size.width, 30)];        _collectionView = [[UICollectionView alloc] initWithFrame:self.view.frame collectionViewLayout:flowLayout];    _collectionView.backgroundColor = [UIColor whiteColor];    _collectionView.delegate = self;    _collectionView.dataSource = self;    [_collectionView registerClass:[UICollectionViewCell class] forCellWithReuseIdentifier:@"identifier"];    [_collectionView registerClass:[HeaderView class] forSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:@"headerIdentifier"];    [self.view addSubview:_collectionView];}- (void)viewDidLoad {    [super viewDidLoad];    // Do any additional setup after loading the view, typically from a nib.}- (NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView{    return 4;}- (UICollectionReusableView *)collectionView:(UICollectionView *)collectionView viewForSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath{    UICollectionReusableView *reusableView = nil;    if (kind == UICollectionElementKindSectionHeader)    {        HeaderView *headerView = [collectionView dequeueReusableSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:@"headerIdentifier" forIndexPath:indexPath];        reusableView = headerView;    }    return reusableView;}- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section{    return 20;}- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath{    UICollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"identifier" forIndexPath:indexPath];    cell.backgroundColor = [UIColor redColor];    return cell;}// 代理方法设置header的尺寸- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout referenceSizeForHeaderInSection:(NSInteger)section{    return CGSizeMake(self.view.frame.size.width, 30);}- (void)didReceiveMemoryWarning {    [super didReceiveMemoryWarning];    // Dispose of any resources that can be recreated.}@end
   

效果图

注意设置section的header尺寸的这句话

[flowLayout setHeaderReferenceSize:CGSizeMake(self.view.frame.size.width, 30)];

平时我们看demo或者测试的时候, 就一个视图, 直接设置这个就可以了而且不会看出什么问题, 在我的项目中, 会在push出来的控制器中有一个collectionView用来筛选, 这个筛选要设置每个section的header-title, 当我pop回前一个视图后就会crash出现文章开头的错误, 经过无数次百度和google之后都没有查到解决办法, 最后经过百般尝试终于找到问题所在, 就是因为用上面的set方法设置了header的尺寸

解决办法:

[flowLayout setHeaderReferenceSize:CGSizeMake(self.view.frame.size.width, 30)]; // 将这句代码删除

在代理方法中设置header的尺寸

// 代理方法设置header的尺寸- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout referenceSizeForHeaderInSection:(NSInteger)section{    return CGSizeMake(self.view.frame.size.width, 30);}

这里要注意一下, 还有2个方法和这个方法很像, 不要选择错了