c#中文件下载工具类，可以实现文件进度和下载完成（成功、失败）的回调，具体使用请往下翻

public class FileDownloadUtil
{
    private string url; //文件下载网络地址
    private string path; //文件下载位置，如d:/download
    private string filename; //文件名，如test.jpg
    private string fileId; //文件ID，文件唯一标识，一般为UUID

    public delegate void ProgressChangedHandler(int progress, string fileId);
    public event ProgressChangedHandler ProgressChanged;
    protected virtual void OnProgressChanged(int progress, string fileId)
    {
        ProgressChanged?.Invoke(progress, fileId);
    }
    public delegate void DownloadFinishHandler(bool isSuccess, string downloadPath, string fileId, string msg = null);
    public event DownloadFinishHandler DownloadFinish;
    protected virtual void OnDownloadFinish(bool isSuccess, string downloadPath, string fileId, string msg = null)
    {
        DownloadFinish?.Invoke(isSuccess, downloadPath, fileId, msg);
    }

    //通过网络链接直接下载任意文件
    public FileDownloadUtil(string url, string path, string filename, string fileId)
    {
        this.url = url;
        this.path = path;
        this.filename = filename;
        this.fileId = fileId;
    }

    public void Download()
    {
        Download(url, path, filename, fileId);
    }
    private void Download(string url, string path, string filename, string fileId)
    {

        if (!Directory.Exists(path))   //判断文件夹是否存在
            Directory.CreateDirectory(path);
        path = path + "/" + filename;
        string tempFile = path + ".temp"; //临时文件
        if (File.Exists(tempFile))
        {
            File.Delete(tempFile);    //存在则删除
        }
        if (File.Exists(path))
        {
            File.Delete(path);    //存在则删除
        }
        FileStream fs = null;
        HttpWebRequest request = null;
        HttpWebResponse response = null;
        Stream responseStream = null;
        try
        {
            //创建临时文件
            fs = new FileStream(tempFile, FileMode.Append, FileAccess.Write, FileShare.ReadWrite);
            request = WebRequest.Create(url) as HttpWebRequest;
            //发送请求并获取相应回应数据
            response = request.GetResponse() as HttpWebResponse;
            //直到request.GetResponse()程序才开始向目标网页发送Post请求
            responseStream = response.GetResponseStream();
            byte[] bArr = new byte[1024];
            long totalBytes = response.ContentLength; //通过响应头获取文件大小，前提是响应头有文件大小
            int size = responseStream.Read(bArr, 0, (int)bArr.Length); //读取响应流到bArr，读取大小
            float percent = 0;  //用来保存计算好的百分比
            long totalDownloadedByte = 0;  //总共下载字节数
            while (size > 0)  //while循环读取响应流
            {
                fs.Write(bArr, 0, size); //写到临时文件
                totalDownloadedByte += size; 
                size = responseStream.Read(bArr, 0, (int)bArr.Length);
                percent = (float)totalDownloadedByte / (float)totalBytes * 100;
                OnProgressChanged((int)percent, fileId);  //下载进度回调
            }
            if (File.Exists(path))
            {
                File.Delete(path);    //存在则删除
            }
            File.Move(tempFile, path); //重命名为正式文件
            OnDownloadFinish(true, path, fileId, null);  //下载完成，成功回调
        }
        catch (Exception ex)
        {
            OnDownloadFinish(false, null, fileId, ex.Message);  //下载完成，失败回调
        }
        finally
        {
            if (fs != null)
                fs.Close();
            if (request != null)
                request.Abort();
            if (response != null)
                response.Close();
            if (responseStream != null)
                responseStream.Close();
        }
    }
}

如何使用：

public void TestDownload()
{
    FileDownloadUtil file = new FileDownloadUtil("需要下载的网络地址","文件下载到的文件夹路径","带后缀的文件名","文件ID，按需求自行删除");
    file.ProgressChanged += File_ProgressChanged;
    file.DownloadFinish += File_DownloadFinish;
    file.Download();
}

private void File_DownloadFinish(bool isSuccess, string downloadPath, string fileId, string msg = null)
{
    if (isSuccess)
    {
        Console.WriteLine("文件 " + fileId + " 下载成功，保存位置："+downloadPath);
    }
    else
    {
        Console.WriteLine("文件 " + fileId + " 下载失败 " + msg==null ? "":"原因："+msg);
    }

}

private void File_ProgressChanged(int progress, string fileId)
{
    Console.WriteLine("文件 " + fileId + " 下载进度：" + progress);
}