UICollectionview设置contentInset方式

下拉(解决设置contentInset 遮挡mj_header显示关键代码)

MJRefreshNormalHeader *header = [MJRefreshNormalHeader headerWithRefreshingBlock:^{
    [self requestForData];
}];
header.ignoredScrollViewContentInsetTop = 30.f;
self.collectionView.mj_header = header;