使用https客户端下载多个文件

Question

我正在开发xamarin.forms应用程序。我想使用HttpClient同时下载多个文件。如果有多个文件，那么我就会得到.NET Framework 2.0的文件。System.IO.IOException:Sharing violation on path(违反路径共享)。 . 有什么需要改进的地方吗？这是我下载文件的代码。

    public async Task DownloadFileAsync(string sourceUrl, string filePathWhereToSave, CancellationTokenSource cts)
    {
        Exception error = null;
        bool isCancelled = false;            
        try
        {
            if (!downloadingTasks.ContainsKey(sourceUrl))
                downloadingTasks.Add(sourceUrl, cts);

            var token = cts.Token;
            var response = await _client.GetAsync(sourceUrl, HttpCompletionOption.ResponseHeadersRead, token);
            response.EnsureSuccessStatusCode();

            string fileName = filePathWhereToSave.Substring(filePathWhereToSave.LastIndexOf('/'));
            string directory = filePathWhereToSave.Substring(0, filePathWhereToSave.LastIndexOf('/'));
            if (!string.IsNullOrEmpty(directory) && !Directory.Exists(directory))
                Directory.CreateDirectory(directory);

            var totalData = response.Content.Headers.ContentLength.GetValueOrDefault(-1L);
            var canSendProgress = totalData != -1L;

            await Task.Run(async() =>
            {
                using (var fileStream = OpenStream(filePathWhereToSave))
                {
                    using (var stream = await response.Content.ReadAsStreamAsync())
                    {
                        var totalRead = 0L;
                        var buffer = new byte[bufferSize];
                        var isMoreDataToRead = true;

                        do
                        {
                            var read = await stream.ReadAsync(buffer, 0, buffer.Length, token);

                            if (read == 0)
                                isMoreDataToRead = false;
                            else
                            {
                                await fileStream.WriteAsync(buffer, 0, read);

                                totalRead += read;

                                if (canSendProgress)
                                {
                                    //var progress = ((totalRead * 1d) / (totalData * 1d) * 100);
                                    MessagingCenter.Send<DownloadFileProgressChangedMessage>(new DownloadFileProgressChangedMessage(sourceUrl, totalRead, totalData, 0), MessageNameConstants.DownloadFileProgressChangedMessage);
                                }
                            }
                        } while (isMoreDataToRead);
                    }
                }
            });
        }
        catch (OperationCanceledException ex)
        {
            isCancelled = true;
        }
        catch (Exception e)
        {
            error = e;
            System.Diagnostics.Debug.WriteLine(e.ToString());                
        }
        finally
        {
            MessagingCenter.Send<DownloadCompletedMessage>(new DownloadCompletedMessage(sourceUrl, filePathWhereToSave, error, isCancelled), MessageNameConstants.DownloadCompletedMessage);

            if (downloadingTasks.ContainsKey(sourceUrl))
                downloadingTasks.Remove(sourceUrl);
        }
    }       

Answer 1

这可能是由于文件将被读流锁定，所以写流不能被创建而出现异常。

为了避免这种情况，你可以使用FileStream类启用读写访问。

  FileStream fileStream = new FileStream(filePathWhereToSave,
                                   FileMode.OpenOrCreate,
                                   FileAccess.ReadWrite,
                                   FileShare.None);

或者使用 StreamWriter

using (var writer = new StreamWriter(filePathWhereToSave))
{
   // do work here.
}

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另外，什么是 OpenStream ? 我在任何汇编中都找不到它，它是否包含在第三方库中？

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请参考

https:/stackoverflow.coma237796978187800。

https:/stackoverflow.coma115413308187800。