搜索控制器仅在iOS 11或更高版本上可用

import UIKit

class ViewController: UIViewController, UISearchResultsUpdating {
    
    var searchController: UISearchController!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        // 初始化搜索控制器
        searchController = UISearchController(searchResultsController: nil)
        searchController.searchResultsUpdater = self
        searchController.obscuresBackgroundDuringPresentation = false
        searchController.searchBar.placeholder = "Search"
        
        // 将搜索栏添加到导航栏
        navigationItem.searchController = searchController
        definesPresentationContext = true
    }
    
    // 更新搜索结果的方法
    func updateSearchResults(for searchController: UISearchController) {
        // 在这里处理搜索逻辑
        let searchBar = searchController.searchBar
        let searchText = searchBar.text ?? ""
        
        // 根据searchText更新显示的结果
        print("Searching for: \(searchText)")
    }
}

if #available(iOS 11.0, *) {
    // 使用UISearchController
} else {
    // 提供替代的搜索方案
}

definesPresentationContext = true