水平设置UICollectionView的标头时，应用程序崩溃

Question

I am pretty new in UICollectionView. And I am really tired to find out the solution. I am trying to add Header in 3 Horizontally Row. I am using Collection view flow layout.
Here is my code which I implement:

    - (void)awakeFromNib {

    self.collectionView.backgroundColor = [UIColor colorWithRed:204.0/255.0 green:204.0/255.0 blue:204.0/255.0 alpha:1.0];

    self.collectionView.backgroundColor = [UIColor clearColor];
    self.collectionView.backgroundView = [[UIView alloc] initWithFrame:CGRectZero];
    UICollectionViewFlowLayout *flowLayout = [[UICollectionViewFlowLayout alloc] init];
    flowLayout.scrollDirection = UICollectionViewScrollDirectionHorizontal;
    flowLayout.itemSize = CGSizeMake(130.0, 170.0);
    [self.collectionView setCollectionViewLayout:flowLayout];

    // Register the colleciton cell
    [_collectionView registerNib:[UINib nibWithNibName:@"ORGArticleCollectionViewCell" bundle:nil] forCellWithReuseIdentifier:@"ORGArticleCollectionViewCell"];
    [self.collectionView registerClass:[_HeaderView class] forSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:@"HeaderView"];
}
#pragma mark - UICollectionViewDataSource methods
- (NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView {
    return 1;
}

- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section {
    if (section == 0) {
        return [self.collectionData count];
    }
    else if(section == 1)
    {
        return [self.collectionData1 count];
    }
    else
    {
        return [self.collectionData2 count];
    }
}

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
    ORGArticleCollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"ORGArticleCollectionViewCell" forIndexPath:indexPath];

    cell.articleTitle.text = [self.collectionData objectAtIndex:[indexPath row]];
    NSString *URL = [self.collectionImageData objectAtIndex:indexPath.row];
    [cell.articleImage setImageWithURL:[NSURL URLWithString:URL] placeholderImage:[UIImage imageNamed:@"profile-image-placeholder"]];
    cell.articleImage.contentMode = UIViewContentModeScaleToFill;
    cell.articlePrice.text = [self.collectionDataPric objectAtIndex:[indexPath row]];
    return cell;
}

- (void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath
{
    NSDictionary *cellData = [self.collectionData objectAtIndex:[indexPath row]];
    [[NSNotificationCenter defaultCenter] postNotificationName:@"didSelectItemFromCollectionView" object:cellData];
}
- (CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout minimumInteritemSpacingForSectionAtIndex:(NSInteger)section
{
    return 0;
}

- (CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout minimumLineSpacingForSectionAtIndex:(NSInteger)section
{
    return 0;
}
- (UICollectionReusableView *)collectionView:(UICollectionView *)collectionView viewForSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath {

    UICollectionReusableView *headerView = [collectionView dequeueReusableSupplementaryViewOfKind:
                                            UICollectionElementKindSectionHeader withReuseIdentifier:@"HeaderView" forIndexPath:indexPath];
    UILabel *label = (UILabel *)[headerView viewWithTag:10];
    if (!label) {
        label = [[UILabel alloc] initWithFrame:CGRectInset(headerView.bounds, 5, 5)];
        label.tag = 10;
        label.font = [UIFont boldSystemFontOfSize:12];
        label.textColor = [UIColor darkGrayColor];
        [headerView addSubview:label];
    }

    label.text = [NSString stringWithFormat:@"Section %d", indexPath.section];
    return headerView;
}

- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout referenceSizeForFooterInSection:(NSInteger)section {
    CGSize headerSize = CGSizeMake(320, 44);
    return headerSize;
}

My App crash in viewForSupplementaryElementOfKind method when I initialize the header view.
Following are the crash log:

Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'no UICollectionViewLayoutAttributes instance for -layoutAttributesForSupplementaryElementOfKind: UICollectionElementKindSectionHeader at path {length = 2, path = 0 - 0}'

Answer 1

The problem with your code is [headerView addSubview:label]; this is called only when label is equal to nil. but you have to call this statement every time when viewForSupplementaryElementOfKind is called.

Update your viewForSupplementaryElementOfKind function with following code.

- (UICollectionReusableView *)collectionView:(UICollectionView *)collectionView viewForSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath {

    UICollectionReusableView *headerView = [collectionView dequeueReusableSupplementaryViewOfKind:
                                            UICollectionElementKindSectionHeader withReuseIdentifier:@"HeaderView" forIndexPath:indexPath];
    UILabel *label = (UILabel *)[headerView viewWithTag:10];
    if (!label) {
        label = [[UILabel alloc] initWithFrame:CGRectInset(headerView.bounds, 5, 5)];
        label.tag = 10;
        label.font = [UIFont boldSystemFontOfSize:12];
        label.textColor = [UIColor darkGrayColor];

    }
    label.text = [NSString stringWithFormat:@"Section %d", indexPath.section];
    [headerView addSubview:label];
    return headerView;
}