using System.Net;

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

使用GetIsNetworkAvailable()检查网络连接，以避免在未连接到网络时创建空文件。

if (System.Net.NetworkInformation.NetworkInterface.GetIsNetworkAvailable())
{
    using (System.Net.WebClient client = new System.Net.WebClient())
    {                        
          client.DownloadFileAsync(new Uri("http://www.examplesite.com/test.txt"),
          "D:\\test.txt");
    }                  
}

包括这个命名空间

using System.Net;

异步下载，并在UI线程本身中放置一个ProgressBar来显示下载的状态

private void BtnDownload_Click(object sender, RoutedEventArgs e)
{
    using (WebClient wc = new WebClient())
    {
        wc.DownloadProgressChanged += wc_DownloadProgressChanged;
        wc.DownloadFileAsync (
            // Param1 = Link of file
            new System.Uri("http://www.sayka.com/downloads/front_view.jpg"),
            // Param2 = Path to save
            "D:\\Images\\front_view.jpg"
        );
    }
}
// Event to track the progress
void wc_DownloadProgressChanged(object sender, DownloadProgressChangedEventArgs e)
{
    progressBar.Value = e.ProgressPercentage;
}

有很多答案，但这是我最近使用的。net 6或更高版本的解决方案。

using var httpClient = new HttpClient();

var tempPath = Path.GetTempFileName();

await using var s = await HttpClient.GetStreamAsync(pdfFilePath);

await using var fs = File.OpenWrite(tempPath);

await s.CopyToAsync(fs);

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)。

WebRequest, WebClient和ServicePoint在。net 6(源代码- 2021年11月)中已经过时。

使用System.Net.Http.HttpClient类代替:

using (var client = new HttpClient())
{
    using (var s = client.GetStreamAsync("https://via.placeholder.com/150"))
    {
        using (var fs = new FileStream("localfile.jpg", FileMode.OpenOrCreate))
        {
            s.Result.CopyTo(fs);
        }
    }
}

相同代码的异步版本:

using var client = new HttpClient();
using var s = await client.GetStreamAsync("https://via.placeholder.com/150");
using var fs = new FileStream("localfile.jpg", FileMode.OpenOrCreate);
await s.CopyToAsync(fs);