C#使用asycn/await模拟下载文件显示进度的方法实现

下面是一个使用async/await模拟下载文件并显示下载进度的方法实现：

public async Task DownloadFileAsync(string url, string filePath)
{
    using (var client = new WebClient())
    {
        var uri = new Uri(url);
        var totalBytes = 0L;
        var bytesReceived = 0L;
        var buffer = new byte[8192];
        var stopwatch = new Stopwatch();

        // 获取文件大小
        var fileInfo = await client.DownloadDataTaskAsync(uri);
        totalBytes = fileInfo.LongLength;

        // 开始下载
        using (var stream = new FileStream(filePath, FileMode.Create, FileAccess.Write, FileShare.None, 8192, true))
        using (var downloadStream = await client.OpenReadTaskAsync(uri))
        {
            stopwatch.Start();

            int bytesRead;
            do
            {
                bytesRead = await downloadStream.ReadAsync(buffer, 0, buffer.Length);
                await stream.WriteAsync(buffer, 0, bytesRead);

                bytesReceived += bytesRead;
                var progress = (double)bytesReceived / totalBytes;
                var speed = (double)bytesReceived / stopwatch.Elapsed.TotalSeconds;

                // 显示下载进度
                Console.Write($"\rDownloading... {progress:P2} ({speed / 1024 / 1024:N2} MB/s)");
            } while (bytesRead > 0);

            stopwatch.Stop();
        }
    }
}

在这个方法中，我们使用WebClient类下载文件，并使用FileStream类将文件写入磁盘。我们使用OpenReadTaskAsync方法异步地读取下载流，并使用ReadAsync和WriteAsync方法异步地读取和写入数据。我们还使用Stopwatch类测量下载时间和速度，并在控制台上显示下载进度。