在block直接使用self会使编译器报以下错误

//Capture 'self' strongly in this block is likely to lead to a retain circle

解决办法是在block中使用self的弱引用(weak reference)

__unsafe_unretained typeof(self) weakSelf = self;
self.refreshCallback = ^void(id data) {
    [weakSelf.goodsCollectionView.mj_header endRefreshing];
    ...
};