搜索栏始终可见

？

看一下Apple的例子(源代码):https://developer.apple.com/library/content/samplecode/TableSearch_UISearchController/Introduction/Intro.html

注意 - 从iOS 11开始,你应该使用UINavigationController而不是表头视图:

        if #available(iOS 11.0, *) {
          // For iOS 11 and later, we place the search bar in the navigation bar.
          navigationController?.navigationBar.prefersLargeTitles = true
          navigationItem.searchController = searchController
          // We want the search bar visible all the time.
          navigationItem.hidesSearchBarWhenScrolling = false
      } else {
          // For iOS 10 and earlier, we place the search bar in the table view's header.
          tableView.tableHeaderView = searchController.searchBar
      }