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);

使用System.Net.WebClient.DownloadFile:

string remoteUri = "http://www.contoso.com/library/homepage/images/";
string fileName = "ms-banner.gif", myStringWebResource = null;

// Create a new WebClient instance.
using (WebClient myWebClient = new WebClient())
{
    myStringWebResource = remoteUri + fileName;
    // Download the Web resource and save it into the current filesystem folder.
    myWebClient.DownloadFile(myStringWebResource, fileName);        
}

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);

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");
    }                  
}

static void Main(string[] args)
        {
            DownloadFileAsync().GetAwaiter();
 
            Console.WriteLine("File was downloaded");
            Console.Read();
        }
 
        private static async Task DownloadFileAsync()
        {
            WebClient client = new WebClient();
            await client.DownloadFileTaskAsync(new Uri("http://somesite.com/myfile.txt"), "mytxtFile.txt");
        }

在.NET Core MVC中，你有时可以简单地这样做:

public async Task<ActionResult> DownloadUrl(string url) {
    return Redirect(url);
}

这可能假设您正在尝试下载的MIME类型被浏览器设置为可下载(例如.mp4)，因此它不会尝试重定向到网页。