导航项标题视图约束不起作用

Question

我想使用 UITextField 创建一个搜索栏。我尝试将导航项的标题视图设置为文本字段并设置相应的约束。但文本字段在导航栏的中心仍然很短。如何让文本字段填满整个导航栏？这是我的代码：

cancelbtn = UIBarButtonItem(title: "Cancel", style: .plain, target: self, action: #selector(CourseTableViewController.searchCancelled))
self.navigationItem.leftBarButtonItem = cancelbtn
let searchField = UITextField()
searchField.translatesAutoresizingMaskIntoConstraints = false
searchField.borderStyle = .roundedRect
self.navigationItem.titleView = searchField
self.navigationItem.titleView!.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: cancelbtn.width)
self.navigationItem.titleView!.widthAnchor.constraint(equalToConstant: view.frame.size.width - cancelbtn.width)

而且是它的样子 rn： UIView

Answer 1

您应该阅读Apple指南。从iOS11开始，您应该将搜索栏安装到navigationItem中。尝试使用以下代码：

import UIKit
class ViewController: UIViewController, UISearchControllerDelegate {
var searchController = UISearchController()
override func viewDidLoad() {
super.viewDidLoad()
navigationController?.navigationBar.prefersLargeTitles = false
searchController = UISearchController(searchResultsController: nil)
searchController.delegate = self
// Customisation 
searchController.searchBar.tintColor = .black
searchController.dimsBackgroundDuringPresentation = false
navigationItem.searchController = searchController
navigationItem.hidesSearchBarWhenScrolling = false
}
}

Answer 2

我解决了我的问题。我没有使用titleView，而是将文本字段放在右侧barButtonItem中，并将其宽度设置为view.frame.size.width。这给了我一个占据整个导航的文本字段。我在这里附加了代码，以防有人也想这样做。

searchBar = UISearchBar()
searchBar.showsCancelButton = false
searchBar.placeholder = "Course name"
searchBar.delegate = self
cancelbtn = UIBarButtonItem(title: "Cancel", style: .plain, target: self, action: #selector(CourseTableViewController.searchCancelled))
self.navigationItem.leftBarButtonItem = cancelbtn
searchTextField = UITextField()
searchTextField.borderStyle = .roundedRect
searchTextField.widthAnchor.constraint(equalToConstant: view.frame.size.width - cancelbtn.width)
searchTextField.translatesAutoresizingMaskIntoConstraints = false
self.navigationItem.rightBarButtonItem = UIBarButtonItem(customView: searchTextField)
self.navigationItem.rightBarButtonItem?.width = view.frame.size.width