ios – 自动调整UICollectionView标头大小

// showhere to keep a reference
UICollectionReusableView * _cachedHeaderView;


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

    if(!_cachedHeaderView){
        // dequeue the cell from storyboard
        _cachedHeaderView = [collectionView dequeueReusableCellWithReusEIDentifier:[NSString StringWithFormat:@"header_cell"] forIndexPath:indexPath];

        // set captions/images on the header etc...

        // tell the collectionview to redraw this section
        [self.collectionView reloadSections:[NSIndexSet indexSetWithIndex:indexPath.section]];
    }

    return _cachedHeaderView;
}


- (CGSizE)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout referenceSizeForHeaderInSection:(NSInteger)section{

    // once there is a reference ot the view,use it to figure out the height
    if(_cachedHeaderView){
        return [_cachedHeaderView systemLayoutSizeFitTingSize:collectionView.bounds.size withHorizontalFitTingPriority:UILayoutPriorityrequired verticalFitTingPriority:UILayoutPriorityDefaultLow];

    }

    // a placeholder value just to get the dequeueReusableCellWithReusEIDentifier to work 
    return CGSizeMake(collectionView.bounds.size.width,100);
}