如何从单个文件自定义NavigationBar？

要在单个文件中自定义NavigationBar，您可以使用SwiftUI或者UIKit

使用SwiftUI：

首先，在您的项目中创建一个新的SwiftUI View，例如CustomNavigationBar.swift。

import SwiftUI

struct CustomNavigationBar: View {
    var title: String
    
    var body: some View {
        VStack {
            HStack {
                Button(action: {
                    // 返回按钮操作
                }) {
                    Image(systemName: "arrow.backward")
                        .foregroundColor(.white)
                        .font(.system(size: 20))
                }
                
                Text(title)
                    .foregroundColor(.white)
                    .font(.system(size: 24))
                    .bold()
                
                Spacer()
            }
            .padding(.horizontal, 16)
            .frame(height: 60)
            .background(Color.blue)
        }
    }
}

在您的主View中使用CustomNavigationBar：

import SwiftUI

struct ContentView: View {
    var body: some View {
        NavigationView {
            VStack {
                CustomNavigationBar(title: "My Custom Navigation")
                Text("Hello, World!")
                    .padding()
            }
        }
        .navigationViewStyle(StackNavigationViewStyle())
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}

使用UIKit：

创建一个新的UIViewController子类，例如CustomNavigationController.swift。

import UIKit

class CustomNavigationController: UINavigationController {

    override func viewDidLoad() {
        super.viewDidLoad()
        
        let customViewController = CustomViewController()
        self.setViewControllers([customViewController], animated: false)
    }
}

创建一个自定义的UIViewController，并在其中添加自定义导航栏：

import UIKit

class CustomViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        self.navigationItem.title = "My Custom Navigation"
        
        let backButton = UIBarButtonItem(title: "Back", style: .plain, target: self, action: #selector(backAction))
        self.navigationItem.leftBarButtonItem = backButton
        
        // 设置自定义背景颜色
        navigationController?.navigationBar.barTintColor = .blue
        
        // 设置自定义标题颜色
        navigationController?.navigationBar.titleTextAttributes = [NSAttributedString.Key.foregroundColor: UIColor.white]
    }
    
    @objc func backAction() {
        navigationController?.popViewController(animated: true)
    }
}

在您的AppDelegate.swift中设置CustomNavigationController为根视图控制器：

import UIKit

@main
class AppDelegate: UIResponder, UIApplicationDelegate {

    var window: UIWindow?

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
        window = UIWindow(frame: UIScreen.main.bounds)
        window?.rootViewController = CustomNavigationController()
        window?.makeKeyAndVisible()
        return true
    }
}

这样，您就可以在单个文件中自定义NavigationBar了。