ios - UICollectionView的HeaderView和cell在屏幕旋转的时候怎么自动改变大小

我给一个UICollectionView添加了autolayout的约束，但是在旋转屏幕的时候，CollectionView的大小根据view改变了，HeaderView和cell的大小没有变化，
应该是我在设置尺寸的时候用的当前view的宽高原因，但是不知道在什么地方改

红色是collectionView的背景色，灰色的是HeaderView的背景色

这是加HeaderView的代码

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

{
    UICollectionReusableView *headerView = [[UICollectionReusableView alloc]init];
    headerView.backgroundColor = [UIColor redColor];
    if (kind == UICollectionElementKindSectionHeader){
        headerView = [collectionView dequeueReusableSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:@"HeaderView" forIndexPath:indexPath];
    }
    
    [headerView addSubview:self.pathLabel];
    
    return headerView;
    
}

这是CollectionView的代码

self.edgesForExtendedLayout = UIRectEdgeNone;

    _flowLayout = [[UICollectionViewFlowLayout alloc]init];
    
    CGFloat flowItemSize = self.view.bounds.size.width / 4 - 5;
    
    _flowLayout.minimumInteritemSpacing = 5.0;//item 之间的行的距离
    _flowLayout.minimumLineSpacing = 5.0;//item 之间竖的距离
    _flowLayout.itemSize = (CGSize){flowItemSize, flowItemSize};
    _flowLayout.headerReferenceSize = CGSizeMake(self.view.bounds.size.width, 50);
    _flowLayout.scrollDirection = UICollectionViewScrollDirectionVertical;
    
    _directoryCollection = [[UICollectionView alloc]initWithFrame:self.view.bounds collectionViewLayout:_flowLayout];
    [_directoryCollection registerClass:[FileIconCell class] forCellWithReuseIdentifier:@"FileIconCell"];
    [_directoryCollection registerClass:[UICollectionReusableView class] forSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:@"HeaderView"];
    
    _directoryCollection.delegate = self;
    _directoryCollection.dataSource = self;
    
    _directoryCollection.backgroundColor = [UIColor redColor];
    [_directoryCollection setUserInteractionEnabled:YES];
    _directoryCollection.showsVerticalScrollIndicator = NO;
    
    [self.view addSubview:_directoryCollection];
    
    [_directoryCollection reloadData];
    _directoryCollection.translatesAutoresizingMaskIntoConstraints = NO;
    
    NSLayoutConstraint *pic_top = [NSLayoutConstraint constraintWithItem:_directoryCollection attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeTop multiplier:1 constant:5.0f];
    
    NSLayoutConstraint *pic_bottom = [NSLayoutConstraint constraintWithItem:_directoryCollection attribute:NSLayoutAttributeBottom relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeBottom multiplier:1 constant:0.0f];
    
    NSLayoutConstraint *pic_left = [NSLayoutConstraint constraintWithItem:_directoryCollection attribute:NSLayoutAttributeLeft relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeLeft multiplier:1 constant:5.0f];
    
    NSLayoutConstraint *pic_right = [NSLayoutConstraint constraintWithItem:_directoryCollection attribute:NSLayoutAttributeRight relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeRight multiplier:1 constant:-5.0f];
    
    [self.view addConstraints:@[pic_top,pic_bottom,pic_left,pic_right]];