UICollectionViewに引っ張って更新を追加する

UICollectionViewに、画面上部を引っ張って更新するRefreshControlを追加する方法

UIRefreshControl *refreshControl = [[UIRefreshControl alloc] init];
refreshControl.tintColor = [UIColor grayColor];
//引っ張ったときのイベント
[refreshControl addTarget:self action:@selector(refershControlAction) forControlEvents:UIControlEventValueChanged];
[self.collectionView addSubview:refreshControl];
self.collectionView.alwaysBounceVertical = YES;

- (void)refershControlAction
{
/*
Some Actions Here
*/
}

参考

ios - UIRefreshControl on UICollectionView only works if the collection fills the height of the container - Stack Overflow