表视图标题中的搜索栏

此示例使用搜索控制器过滤表视图控制器中的单元格。搜索栏位于表视图的标题视图内。表格视图内容的偏移量与搜索栏的高度相同，因此首先隐藏搜索栏。向上滚动超过表格视图的顶部边缘时，将显示搜索栏。然后，当搜索栏变为活动状态时，它会隐藏导航栏。


将 UITableViewController 嵌入到 UINavigationController 中以获取 UINavigationItem（其中包含导航栏）。然后将我们的自定义 ViewController 类设置为从 UITableViewController 继承并采用 UISearchResultsUpdating 协议。

class ViewController: UITableViewController, UISearchResultsUpdating {

    let entries = [(title: "Easiest", image: "green_circle"),
                   (title: "Intermediate", image: "blue_square"),
                   (title: "Advanced", image: "black_diamond"),
                   (title: "Expert Only", image: "double_black_diamond")]
    
    // An empty tuple that will be updated with search results.
    var searchResults : [(title: String, image: String)] = []
    
    let searchController = UISearchController(searchResultsController: nil)

    override func viewDidLoad() {
        super.viewDidLoad()
        
        searchController.searchResultsUpdater = self
        self.definesPresentationContext = true

        // Place the search bar in the table view's header.
        self.tableView.tableHeaderView = searchController.searchBar

        // Set the content offset to the height of the search bar's height
        // to hide it when the view is first presented.
        self.tableView.contentOffset = CGPoint(x: 0, y: searchController.searchBar.frame.height)
    }
    
    func filterContent(for searchText: String) {
        // Update the searchResults array with matches
        // in our entries based on the title value.
        searchResults = entries.filter({ (title: String, image: String) -> Bool in
            let match = title.range(of: searchText, options: .caseInsensitive)
            // Return the tuple if the range contains a match.
            return match != nil
        })
    }

    // MARK: - UISearchResultsUpdating method
    
    func updateSearchResults(for searchController: UISearchController) {
        // If the search bar contains text, filter our data with the string
        if let searchText = searchController.searchBar.text {
            filterContent(for: searchText)
            // Reload the table view with the search result data.
            tableView.reloadData()
        }
    }

    // MARK: - UITableViewController methods
    
    override func numberOfSections(in tableView: UITableView) -> Int { return 1 }

    override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        // If the search bar is active, use the searchResults data.
        return searchController.isActive ? searchResults.count : entries.count
    }
    
    override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        // If the search bar is active, use the searchResults data.
        let entry = searchController.isActive ? 
                    searchResults[indexPath.row] : entries[indexPath.row]
        
        let cell = tableView.dequeueReusableCell(withIdentifier: "Cell", for: indexPath)
        cell.textLabel?.text = entry.title
        cell.imageView?.image = UIImage(named: entry.image)
        return cell
    }
}