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    [self.collectionView registerClass:[CollectionReusableView class] forSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:headerIdentifier];
    [self.collectionView registerClass:[CollectionReusableView class] forSupplementaryViewOfKind:UICollectionElementKindSectionFooter withReuseIdentifier:footerIdentifier];

- (UICollectionReusableView *)collectionView:(UICollectionView *)collectionView viewForSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath {
    CollectionReusableView *reusableView;
    if ([kind isEqualToString:UICollectionElementKindSectionHeader]) {
        // 设置header内容。
        reusableView = [collectionView dequeueReusableSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:headerIdentifier forIndexPath:indexPath];
        reusableView.label.textAlignment = NSTextAlignmentCenter;
        reusableView.label.text = [NSString stringWithFormat:@"Section %li",indexPath.section];
    } else {
        // 设置footer内容。
        reusableView = [collectionView dequeueReusableSupplementaryViewOfKind:UICollectionElementKindSectionFooter withReuseIdentifier:footerIdentifier forIndexPath:indexPath];
        reusableView.label.textAlignment = NSTextAlignmentNatural;
        reusableView.label.text = [NSString stringWithFormat:@"Section %li have %li items",indexPath.section,[collectionView numberOfItemsInSection:indexPath.section]];
    }
    return reusableView;
}