如何在ios应用程序中显示web服务调用进度条

import UIKit

class ViewController: UIViewController, URLSessionDelegate, URLSessionDataDelegate {
    
    var progressView: UIProgressView!

    override func viewDidLoad() {
        super.viewDidLoad()
        
        // 创建进度条
        progressView = UIProgressView(progressViewStyle: .default)
        progressView.frame = CGRect(x: 50, y: 100, width: 200, height: 20)
        view.addSubview(progressView)
        
        // 发起Web服务调用
        let url = URL(string: "https://example.com/api")
        let request = URLRequest(url: url!)
        
        let session = URLSession(configuration: URLSessionConfiguration.default, delegate: self, delegateQueue: OperationQueue.main)
        let task = session.dataTask(with: request)
        task.resume()
    }
    
    // 实现NSURLSessionDataDelegate协议的方法，用于监听进度
    func urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive response: URLResponse, completionHandler: @escaping (URLSession.ResponseDisposition) -> Void) {
        let expectedContentLength = response.expectedContentLength
        if expectedContentLength != -1 {
            DispatchQueue.main.async {
                self.progressView.isHidden = false
            }
        }
        completionHandler(.allow)
    }
    
    func urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive data: Data) {
        // 更新进度条
        let totalBytesReceived = Int64(data.count)
        let totalBytesExpected = dataTask.response?.expectedContentLength ?? NSURLSessionTransferSizeUnknown
        let progress = Float(totalBytesReceived) / Float(totalBytesExpected)
        
        DispatchQueue.main.async {
            self.progressView.progress = progress
        }
        
        // 处理接收到的数据
        // ...
    }
    
    func urlSession(_ session: URLSession, task: URLSessionTask, didCompleteWithError error: Error?) {
        // 隐藏进度条
        DispatchQueue.main.async {
            self.progressView.isHidden = true
        }
        
        if let error = error {
            // 处理错误
            // ...
        } else {
            // 请求完成
            // ...
        }
    }
}