//上下拉头尾部
self.collectionView.footer = [MJRefreshBackNormalFooter footerWithRefreshingTarget:self refreshingAction:@selector(footRequestMore)];
self.collectionView.header = [MJRefreshNormalHeader headerWithRefreshingTarget:self refreshingAction:@selector(headRefreshData)];
//头尾部刷新
[collectionView.header beginRefreshing];//系统自带