下载网络资源-带下载进度

带进度 http://t.zoukankan.com/h82258652-p-10950580.html
使用ConfigureAwait(false)的主要功能是提高异步方法的性能和避免潜在的死锁问题。当知道在异步方法中不需要恢复到原始的上下文时，使用ConfigureAwait(false)可以避免不必要的上下文切换，从而提高代码的执行效率。例如，在后台任务或I/O密集型操作中，使用ConfigureAwait(false)可以显著提升应用的性能和响应速度。

namespace AppUtils
{
    public struct HttpDownloadProgress
    {
        public long BytesReceived { get; set; }
        public long TotalBytesToReceive { get; set; }
    }
    public static class HttpClientExtensions
    {
        private const int BufferSize = 8192;

        public static async Task<byte[]> GetByteArrayAsync(this HttpClient client, Uri requestUri, IProgress<HttpDownloadProgress> progress, CancellationToken cancellationToken)
        {
            if (client == null)
            {
                throw new ArgumentNullException(nameof(client));
            }

            using (var responseMessage = await client.GetAsync(requestUri, HttpCompletionOption.ResponseHeadersRead, cancellationToken).ConfigureAwait(false))
            {
                if (responseMessage.StatusCode== System.Net.HttpStatusCode.NotFound)
                {
                    throw new Exception(System.Net.HttpStatusCode.NotFound.ToString());
                }
                responseMessage.EnsureSuccessStatusCode();

                var content = responseMessage.Content;
                if (content == null)
                {
                    return Array.Empty<byte>();
                }

                var headers = content.Headers;
                var contentLength = headers.ContentLength;
                using (var responseStream = await content.ReadAsStreamAsync().ConfigureAwait(false))
                {
                    var buffer = new byte[BufferSize];
                    int bytesRead;
                    var bytes = new List<byte>();

                    var downloadProgress = new HttpDownloadProgress();
                    if (contentLength.HasValue)
                    {
                        downloadProgress.TotalBytesToReceive = contentLength.Value;
                    }
                    progress?.Report(downloadProgress);
                    while ((bytesRead = await responseStream.ReadAsync(buffer, 0, BufferSize, cancellationToken).ConfigureAwait(false)) > 0)
                    {
                        bytes.AddRange(buffer.Take(bytesRead));

                        downloadProgress.BytesReceived += bytesRead;
                        progress?.Report(downloadProgress);
                    }

                    return bytes.ToArray();
                }
            }
        }
    }
}

　　UpgradeService：System.Net.Http.HttpClient _client = new HttpClient();

public async Task DownloadFileAsync(string url, IProgress<HttpDownloadProgress> progress, CancellationToken token)
        {
            var filePath = "D:\test.txt";
            if (File.Exists(filePath))
            {
                File.Delete(filePath);
            }

            var bytes = await _client.GetByteArrayAsync(new Uri(url), progress, token);
            using var fileStream = new FileStream(filePath, FileMode.Create);
            fileStream.Write(bytes, 0, bytes.Length);
        }

　　

string fileUrl = "http://xxxxx/test.txt";
            CancellationTokenSource CTSource = new CancellationTokenSource();
            //当前线程
            var progress = new Progress<HttpDownloadProgress>(async percent =>
            {
                BytesReceived = percent.BytesReceived / 1024; //当前已经下载的Kb
                TotalBytesToReceive = percent.TotalBytesToReceive / 1024; //文件总大小Kb
                DownloadMsg = "正在下载： " + BytesReceived + "KB / " + TotalBytesToReceive + "KB";
                //StateHasChanged();

                //await moduleJS.InvokeVoidAsync("SetDownloadMsg", DownloadMsg);

            });
            await _UpgradeService.DownloadFileAsync(fileUrl, progress, CTSource.Token);

旧代码：

#region 下载文件
    /// <summary>
    /// Http方式下载文件
    /// </summary>
    /// <param name="url">http地址</param>
    /// <param name="localfile">本地文件</param>
    /// <returns></returns>
    public bool Download(string url, string localfile)
    {
        bool flag = false;
        long startPosition = 0; // 上次下载的文件起始位置
        FileStream writeStream; // 写入本地文件流对象

        long remoteFileLength = GetHttpLength(url);// 取得远程文件长度
        System.Console.WriteLine("remoteFileLength=" + remoteFileLength);
        if (remoteFileLength == 745)
        {
            System.Console.WriteLine("远程文件不存在.");
            return false;
        }

        // 判断要下载的文件夹是否存在
        if (File.Exists(localfile))
        {

            writeStream = File.OpenWrite(localfile);             // 存在则打开要下载的文件
            startPosition = writeStream.Length;                  // 获取已经下载的长度

            if (startPosition >= remoteFileLength)
            {
                System.Console.WriteLine("本地文件长度" + startPosition + "已经大于等于远程文件长度" + remoteFileLength);
                writeStream.Close();

                return false;
            }
            else
            {
                writeStream.Seek(startPosition, SeekOrigin.Current); // 本地文件写入位置定位
            }
        }
        else
        {
            writeStream = new FileStream(localfile, FileMode.Create);// 文件不保存创建一个文件
            startPosition = 0;
        }


        try
        {
            HttpWebRequest myRequest = (HttpWebRequest)HttpWebRequest.Create(url);// 打开网络连接

            if (startPosition > 0)
            {
                myRequest.AddRange((int)startPosition);// 设置Range值,与上面的writeStream.Seek用意相同,是为了定义远程文件读取位置
            }


            Stream readStream = myRequest.GetResponse().GetResponseStream();// 向服务器请求,获得服务器的回应数据流


            byte[] btArray = new byte[512];// 定义一个字节数据,用来向readStream读取内容和向writeStream写入内容
            int contentSize = readStream.Read(btArray, 0, btArray.Length);// 向远程文件读第一次

            long currPostion = startPosition;

            while (contentSize > 0)// 如果读取长度大于零则继续读
            {
                currPostion += contentSize;
                int percent = (int)(currPostion * 100 / remoteFileLength);
                System.Console.WriteLine("percent=" + percent + "%");

                writeStream.Write(btArray, 0, contentSize);// 写入本地文件
                contentSize = readStream.Read(btArray, 0, btArray.Length);// 继续向远程文件读取
            }

            //关闭流
            writeStream.Close();
            readStream.Close();

            flag = true;        //返回true下载成功
        }
        catch (Exception)
        {
            writeStream.Close();
            flag = false;       //返回false下载失败
        }

        return flag;
    }

    // 从文件头得到远程文件的长度
    private static long GetHttpLength(string url)
    {
        long length = 0;

        try
        {
            HttpWebRequest req = (HttpWebRequest)HttpWebRequest.Create(url);// 打开网络连接
            HttpWebResponse rsp = (HttpWebResponse)req.GetResponse();

            if (rsp.StatusCode == HttpStatusCode.OK)
            {
                length = rsp.ContentLength;// 从文件头得到远程文件的长度
            }

            rsp.Close();
            return length;
        }
        catch (Exception e)
        {
            return length;
        }

    }
    #endregion