根据我的研究，我发现WebClient。DownloadFileAsync是下载文件的最佳方式。可以在系统中找到。Net命名空间，它也支持。Net core。

下面是下载该文件的示例代码。

using System;
using System.IO;
using System.Net;
using System.ComponentModel;

public class Program
{
    public static void Main()
    {
        new Program().Download("ftp://localhost/test.zip");
    }
    public void Download(string remoteUri)
    {
        string FilePath = Directory.GetCurrentDirectory() + "/tepdownload/" + Path.GetFileName(remoteUri); // path where download file to be saved, with filename, here I have taken file name from supplied remote url
        using (WebClient client = new WebClient())
        {
            try
            {
                if (!Directory.Exists("tepdownload"))
                {
                    Directory.CreateDirectory("tepdownload");
                }
                Uri uri = new Uri(remoteUri);
                //password username of your file server eg. ftp username and password
                client.Credentials = new NetworkCredential("username", "password");
                //delegate method, which will be called after file download has been complete.
                client.DownloadFileCompleted += new AsyncCompletedEventHandler(Extract);
                //delegate method for progress notification handler.
                client.DownloadProgressChanged += new DownloadProgressChangedEventHandler(ProgessChanged);
                // uri is the remote url where filed needs to be downloaded, and FilePath is the location where file to be saved
                client.DownloadFileAsync(uri, FilePath);
            }
            catch (Exception)
            {
                throw;
            }
        }
    }
    public void Extract(object sender, AsyncCompletedEventArgs e)
    {
        Console.WriteLine("File has been downloaded.");
    }
    public void ProgessChanged(object sender, DownloadProgressChangedEventArgs e)
    {
        Console.WriteLine($"Download status: {e.ProgressPercentage}%.");
    }
}

以上代码文件将下载到项目目录下的tepdownload文件夹中。请阅读代码中的注释以了解以上代码的功能。

您可能需要在文件下载期间了解状态并更新ProgressBar，或者在发出请求之前使用凭据。

下面是一个包含这些选项的示例。Lambda符号和字符串插值已被使用:

using System.Net;
// ...

using (WebClient client = new WebClient()) {
    Uri ur = new Uri("http://remotehost.do/images/img.jpg");

    //client.Credentials = new NetworkCredential("username", "password");
    String credentials = Convert.ToBase64String(Encoding.ASCII.GetBytes("Username" + ":" + "MyNewPassword"));
    client.Headers[HttpRequestHeader.Authorization] = $"Basic {credentials}";

    client.DownloadProgressChanged += (o, e) =>
    {
        Console.WriteLine($"Download status: {e.ProgressPercentage}%.");

        // updating the UI
        Dispatcher.Invoke(() => {
            progressBar.Value = e.ProgressPercentage;
        });
    };

    client.DownloadDataCompleted += (o, e) => 
    {
        Console.WriteLine("Download finished!");
    };

    client.DownloadFileAsync(ur, @"C:\path\newImage.jpg");
}

如果你需要设置头文件和cookie来下载文件，你需要做一些稍微不同的事情。这里有一个例子……

// Pass in the HTTPGET URL, Full Path w/Filename, and a populated Cookie Container (optional)
private async Task DownloadFileRequiringHeadersAndCookies(string getUrl, string fullPath, CookieContainer cookieContainer, CancellationToken cancellationToken)
{
    cookieContainer ??= new CookieContainer();  // TODO: FILL ME AND PASS ME IN

    using (var handler = new HttpClientHandler()
    {
        UseCookies = true,
        CookieContainer = cookieContainer, // This will, both, use the cookies passed in, and update/create cookies from the response
        ServerCertificateCustomValidationCallback = (message, cert, chain, errors) => true, // use only if it gets angry about the SSL endpoints
        AllowAutoRedirect = true,
    })
    {
        using (var client = new HttpClient(handler))
        {
            SetHeaders(client);

            using (var response = await client.GetAsync(getUrl, cancellationToken))
            {
                if (response.IsSuccessStatusCode)
                {
                    var bytes = await response.Content.ReadAsByteArrayAsync(cancellationToken);
                    await File.WriteAllBytesAsync(fullPath, bytes, cancellationToken); // This overwrites the file
                }
                else
                {
                    // TODO: HANDLE ME
                    throw new FileNotFoundException();
                }
            }
        }
    }
}

并且，要添加你需要的header…

private void SetHeaders(HttpClient client)
{
    // TODO: SET ME
    client.DefaultRequestHeaders.Connection.Add("keep-alive");
    client.DefaultRequestHeaders.Add("User-Agent", "Mozilla/5.0 (Windows NT 10.0; Win64; x64) ...");
    client.DefaultRequestHeaders.Add("Accept", "text/html,application/xhtml+xml,application/xml;q=0.9, ...");
    client.DefaultRequestHeaders.AcceptEncoding.Add(new StringWithQualityHeaderValue("gzip"));
    client.DefaultRequestHeaders.AcceptEncoding.Add(new StringWithQualityHeaderValue("deflate"));
    client.DefaultRequestHeaders.AcceptLanguage.Add(new StringWithQualityHeaderValue("en-US"));
    client.DefaultRequestHeaders.AcceptLanguage.Add(new StringWithQualityHeaderValue("en", .9));
    ...
}

旁白:你可以通过以下方式填充cookie容器:

循环遍历前一个响应的cookie。 这个响应可以来自HttpAgilityPack，或者WebClient，或者Puppeteer(有很多选项) 手动输入(来自配置值或硬编码值)。

using System.Net;

WebClient webClient = new WebClient();
webClient.DownloadFile("http://mysite.com/myfile.txt", @"c:\myfile.txt");

下面的代码包含下载文件的逻辑与原始名称

private string DownloadFile(string url)
    {

        HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(url);
        string filename = "";
        string destinationpath = Environment;
        if (!Directory.Exists(destinationpath))
        {
            Directory.CreateDirectory(destinationpath);
        }
        using (HttpWebResponse response = (HttpWebResponse)request.GetResponseAsync().Result)
        {
            string path = response.Headers["Content-Disposition"];
            if (string.IsNullOrWhiteSpace(path))
            {
                var uri = new Uri(url);
                filename = Path.GetFileName(uri.LocalPath);
            }
            else
            {
                ContentDisposition contentDisposition = new ContentDisposition(path);
                filename = contentDisposition.FileName;

            }

            var responseStream = response.GetResponseStream();
            using (var fileStream = File.Create(System.IO.Path.Combine(destinationpath, filename)))
            {
                responseStream.CopyTo(fileStream);
            }
        }

        return Path.Combine(destinationpath, filename);
    }

这是我的解决方案，效果很好:

public static void DownloadFile(string url, string pathToSaveFile)
        {
            ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12;
            // or: ServicePointManager.SecurityProtocol = (SecurityProtocolType)3072;

            using (WebDownload client = new WebDownload())
            {
                client.Headers["User-Agent"] = "User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/56.0.2924.87 Safari/537.36";
                client.DownloadFile(new Uri(url), pathToSaveFile);
            }
        }
    
    public class WebDownload : WebClient
        {
            protected override WebRequest GetWebRequest(Uri address)
            {
                HttpWebRequest request = (HttpWebRequest)base.GetWebRequest(address);
                if (request != null)
                {
                    request.AutomaticDecompression = DecompressionMethods.GZip | DecompressionMethods.Deflate;
                }
                return request;
            }
        }