直接在 WP8 中保存到独立存储 [英] Save to isolated storage directly in WP8

问题描述

我想将 zip 文件直接保存到与服务器隔离的存储中，但我面临的问题是当我尝试使用以下代码进行保存时，由于我的文件大小有时大于 150 MB，因此出现内存不足异常.所以我在这里发布了一个问题，建议是

I want to save a zip file directly to isolated storage from server , But the problem i am facing was when i try to save using the below code , i get out of memory exception since my file size is > 150 MB some times. So i posted a question here and the suggestion was

您可以将这样的文件直接下载到IsolatedStorage，但如果您想将其放入内存中，可能会出现问题.

you can download such a file directly to IsolatedStorage, but if you want to put that into Memory - there can be a problem.

那么如何将文件从服务器直接保存到独立存储而不保存到内存.我使用的代码发布在这里

So how can i save a file from server directly to isolated storage without saving to memory . The code i used is posted here

client = new WebClient();
    client.OpenReadCompleted += new OpenReadCompletedEventHandler(client_OpenReadCompleted);
    client.OpenReadAsync(new Uri(fileurl), objRef);

    private async void client_OpenReadCompleted(object sender, OpenReadCompletedEventArgs e)
    {

            var file = IsolatedStorageFile.GetUserStoreForApplication();
            if (!file.DirectoryExists("Folderpath/Files"))
            {
                file.CreateDirectory("Folderpath/Files");
            }
            string hpubFile = "/Folderpath/Files/fileName" ;
            using (IsolatedStorageFileStream stream = new IsolatedStorageFileStream(hpubFile, System.IO.FileMode.OpenOrCreate, FileAccess.ReadWrite, file))
            {
                byte[] buffer = new byte[1024];
                while (e.Result.Read(buffer, 0, buffer.Length) > 0)
                {
                    stream.Write(buffer, 0, buffer.Length);
                }
            }
        }
    }

推荐答案

那么也许可以试试这样的方法——用 HttpWebRequest 来做:

Then maybe try such an approach - do it with HttpWebRequest:

1.首先使用可等待的 GetResponseAsync 扩展您的 HttpWebRequest - WP 缺少此方法，但使用 TaskCompletitionSource 您可以编写自己的实现.在您的命名空间中，创建一个静态类:
1. First extend your HttpWebRequest with awaitable GetResponseAsync - WP lacks this method, but with TaskCompletitionSource you can write your own implementation. Somwhere in your Namespace, make a static class:

public static class Extensions
{
    public static Task<HttpWebResponse> GetResponseAsync(this HttpWebRequest webRequest)
    {
        TaskCompletionSource<HttpWebResponse> taskComplete = new TaskCompletionSource<HttpWebResponse>();
        webRequest.BeginGetResponse(
            asyncResponse =>
            {
                try
                {
                    HttpWebRequest responseRequest = (HttpWebRequest)asyncResponse.AsyncState;
                    HttpWebResponse someResponse = (HttpWebResponse)responseRequest.EndGetResponse(asyncResponse);
                    taskComplete.TrySetResult(someResponse);
                }
                catch (WebException webExc)
                {
                    HttpWebResponse failedResponse = (HttpWebResponse)webExc.Response;
                    taskComplete.TrySetResult(failedResponse);
                }
                catch (Exception exc) { taskComplete.SetException(exc); }
            }, webRequest);
        return taskComplete.Task;
    }
}

2.然后修改您的代码以使用它:
2. Then modify your code to use it:

CancellationTokenSource cts = new CancellationTokenSource();
enum Problem { Ok, Cancelled, Other };

public async Task<Problem> DownloadFileFromWeb(Uri uriToDownload, string fileName, CancellationToken cToken)
{
    try
    {
        HttpWebRequest wbr = WebRequest.CreateHttp(uriToDownload);
        wbr.Method = "GET";
        wbr.AllowReadStreamBuffering = false;
        WebClient wbc = new WebClient();

        using (HttpWebResponse response = await wbr.GetResponseAsync())
        {
            using (Stream mystr = response.GetResponseStream())
            {
                using (IsolatedStorageFile ISF = IsolatedStorageFile.GetUserStoreForApplication())
                  {
                      if (ISF.FileExists(fileName)) return Problem.Other;
                      using (IsolatedStorageFileStream file = ISF.CreateFile(fileName))
                      {
                          const int BUFFER_SIZE = 100 * 1024;
                          byte[] buf = new byte[BUFFER_SIZE];

                          int bytesread = 0;
                          while ((bytesread = await mystr.ReadAsync(buf, 0, BUFFER_SIZE)) > 0)
                          {
                              cToken.ThrowIfCancellationRequested();
                              file.Write(buf, 0, bytesread);
                          }
                      }
                  }
                  return Problem.Ok;
              }
          }
      }
      catch (Exception exc)
      {
          if (exc is OperationCanceledException)
              return Problem.Cancelled;
          else return Problem.Other; 
      }
  }

3.并下载:

  private async void Downlaod_Click(object sender, RoutedEventArgs e)
  {
      cts = new CancellationTokenSource();
      Problem fileDownloaded = await DownloadFileFromWeb(new Uri(@"http://filedress/myfile.txt", UriKind.Absolute), "myfile.txt", cts.Token);
      switch(fileDownloaded)
      {
          case Problem.Ok:
              MessageBox.Show("Problem with download");
              break;
          case Problem.Cancelled:
              MessageBox.Show("Download cancelled");
              break;
          case Problem.Other:
          default:
              MessageBox.Show("Other problem with download");
              break;
      }
  }

因为我有我的 WebResponse，所以我从中获取一个流，然后异步读取它.
请注意，我还没有测试过上面的代码，但希望它可以给您一些想法.

As I've my WebResponse, I get a stream from it and then read it async.
Please be aware that I've not tested the code above, but hopefuly it may give you some ideas how this can work.

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