Swift：如何通过代码添加搜索栏至导航栏？子控制器复用HomeViewController搜索栏

Hey there! Let's break down your two questions about integrating a search bar with your navigation bar and accessing it from child view controllers—here's how to tackle them in Swift:

1. Adding a Search Bar to the Navigation Bar via Code #

You have two common approaches here, depending on whether you want a basic search bar or the more modern, feature-rich UISearchController (recommended for iOS 11+):

Option 1: Basic UISearchBar Directly in Navigation Bar #

This is straightforward if you just need a simple search bar without extra results handling:

import UIKit

class HomeViewController: UIViewController, UISearchBarDelegate {
    override func viewDidLoad() {
        super.viewDidLoad()
        
        // Create and configure the search bar
        let searchBar = UISearchBar()
        searchBar.placeholder = "Search items..."
        searchBar.searchBarStyle = .minimal
        searchBar.tintColor = .systemBlue
        
        // Assign it to the navigation item's titleView
        navigationItem.titleView = searchBar
        
        // Set delegate to handle search events
        searchBar.delegate = self
    }
    
    // MARK: - UISearchBarDelegate
    func searchBar(_ searchBar: UISearchBar, textDidChange searchText: String) {
        // Respond to search text changes here
        print("Current search query: \(searchText)")
    }
    
    func searchBarSearchButtonClicked(_ searchBar: UISearchBar) {
        searchBar.resignFirstResponder() // Hide keyboard when user taps search
    }
}

Option 2: Using UISearchController (Modern Approach) #

This gives you built-in features like a search results controller and better integration with the navigation bar:

import UIKit

class HomeViewController: UIViewController, UISearchResultsUpdating {
    override func viewDidLoad() {
        super.viewDidLoad()
        
        let searchController = UISearchController(searchResultsController: nil)
        searchController.searchBar.placeholder = "Search items..."
        searchController.obscuresBackgroundDuringPresentation = false // Keep content visible while searching
        
        // Attach to navigation bar
        navigationItem.searchController = searchController
        
        // Optional: Keep search bar visible even when scrolling
        navigationItem.hidesSearchBarWhenScrolling = false
        
        // Set updater to handle search text changes
        searchController.searchResultsUpdater = self
    }
    
    // MARK: - UISearchResultsUpdating
    func updateSearchResults(for searchController: UISearchController) {
        guard let searchText = searchController.searchBar.text else { return }
        // Handle search text updates here
        print("Search query updated: \(searchText)")
    }
}

2. Accessing the HomeViewController's Search Bar from a Child View Controller #

There are a few clean ways to do this, depending on how tightly coupled you want your view controllers to be:

Approach 1: Direct Parent Reference (Simple but Coupled) #

If your child view controller is directly embedded in HomeViewController, you can cast the parent and access the search bar:

import UIKit

class ChildViewController: UIViewController, UISearchBarDelegate {
    override func viewDidLoad() {
        super.viewDidLoad()
        
        // Get reference to HomeViewController
        guard let homeVC = parent as? HomeViewController else {
            print("Could not access HomeViewController")
            return
        }
        
        // Access search bar if using basic UISearchBar
        if let searchBar = homeVC.navigationItem.titleView as? UISearchBar {
            searchBar.delegate = self // Take over delegate if needed
            print("Current search text: \(searchBar.text ?? "")")
        }
        
        // Access search bar if using UISearchController
        if let searchController = homeVC.navigationItem.searchController {
            let searchBar = searchController.searchBar
            searchBar.placeholder = "Search from child VC" // Modify properties
        }
    }
    
    // MARK: - UISearchBarDelegate
    func searchBar(_ searchBar: UISearchBar, textDidChange searchText: String) {
        // Handle search events in the child VC
        print("Child VC received search text: \(searchText)")
    }
}

Approach 2: Closure/Delegate Pattern (Low Coupling, Recommended) #

This avoids direct references and makes your code more reusable. Define a closure in HomeViewController to broadcast search events:

// In HomeViewController
class HomeViewController: UIViewController, UISearchResultsUpdating {
    // Define a closure to pass search text changes
    var onSearchTextUpdated: ((String) -> Void)?
    
    override func viewDidLoad() {
        super.viewDidLoad()
        // ... setup search controller as before
    }
    
    func updateSearchResults(for searchController: UISearchController) {
        guard let searchText = searchController.searchBar.text else { return }
        onSearchTextUpdated?(searchText) // Broadcast the text change
    }
}

// In ChildViewController
class ChildViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        
        guard let homeVC = parent as? HomeViewController else { return }
        // Subscribe to search text updates
        homeVC.onSearchTextUpdated = { [weak self] searchText in
            self?.updateChildContent(with: searchText)
        }
    }
    
    private func updateChildContent(with searchText: String) {
        // Update your child VC's UI/data based on the search text
        print("Updating child content with: \(searchText)")
    }
}

Approach 3: NotificationCenter (For Cross-Controller Communication) #

Use this if you need multiple view controllers to react to search changes, but it's less direct than the closure pattern:

// In HomeViewController
func updateSearchResults(for searchController: UISearchController) {
    guard let searchText = searchController.searchBar.text else { return }
    // Post a notification with the search text
    NotificationCenter.default.post(
        name: NSNotification.Name("SearchTextUpdated"),
        object: nil,
        userInfo: ["searchText": searchText]
    )
}

// In ChildViewController
class ChildViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        // Listen for the notification
        NotificationCenter.default.addObserver(
            self,
            selector: #selector(handleSearchUpdate(_:)),
            name: NSNotification.Name("SearchTextUpdated"),
            object: nil
        )
    }
    
    @objc private func handleSearchUpdate(_ notification: Notification) {
        if let searchText = notification.userInfo?["searchText"] as? String {
            updateChildContent(with: searchText)
        }
    }
    
    private func updateChildContent(with searchText: String) {
        // Update child VC content here
    }
    
    // Clean up observer when VC is deinitialized
    deinit {
        NotificationCenter.default.removeObserver(self)
    }
}

内容的提问来源于stack exchange，提问作者podgradle