将一个UISearchBar锁定到一个UITableView的顶部，比如Game Center。

There's this cool feature in the UITableViews in Game Center and the search bars they have at their tops. Unlike apps where the search bar is placed in the table header view (so it counts as a standard table cell), instead, it seems to be bolted to the parent navigation bar above it. So when scrolling the table, the search bar does indeed move, but if you scroll above the boundaries of the table, the search bar never stops touching the navigation bar.There's this cool feature in the UITableViews i