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我有一个 C# Windows Phone 7.1 应用程序，它从外部 Web 服务器下载 PDF 文件，然后（尝试）将其作为文件保存到隔离存储区域。我尝试了几种不同的方法来完成这项工作，但是文件总是以大约 30% 的大小结束，当我在文本编辑器中打开它时，而不是在文件开头看到通常的“PDF”字符后跟编码的字符，我看到基本上是垃圾。我使用的测试文件应该是 161k，但是当我使用独立存储资源管理器查看文件时，它是 271k。

首先，我将文件下载到字符串中。我此时在调试器中检查了字符串，它确实包含正确的值，并且长度正确。当我尝试将其写入隔离的存储区域时，就会出现问题。我用相同的无效结果尝试了StreamWriter和BinaryWriter 。结果文件的内容似乎是一长串的垃圾字符。请注意，如果文件存在，我将删除它以防万一，然后再写出内容。下面是我使用BinaryWriter版本的代码。怎么了？

async public static Task URLToFileAsync(
                                string strUrl, 
                                string strDestFilename, 
                                IProgress<int> progress, 
                                CancellationToken cancelToken)
{
    strUrl = strUrl.Trim();

    if (String.IsNullOrWhiteSpace(strUrl))
        throw new ArgumentException("(Misc::URLToFileAsync) The URL is empty.");

    strDestFilename = strDestFilename.Trim();

    if (String.IsNullOrWhiteSpace(strDestFilename))
        throw new ArgumentException("(Misc::URLToFileAsync) The destination file name is empty.");

    // Create the isolated storage file.
    // FileStream fs = Misc.CreateIsolatedStorageFileStream(strDestFilename);
    IsolatedStorageFile isoStorage = IsolatedStorageFile.GetUserStoreForApplication();

    // Delete the file first.
    if (isoStorage.FileExists(strDestFilename))
        isoStorage.DeleteFile(strDestFilename);

    IsolatedStorageFileStream theIsoStream = isoStorage.OpenFile(strDestFilename, FileMode.Create);

    FileStream fs = theIsoStream;

    // If the stream writer is NULL, then the file could not be created.
    if (fs == null)
        throw new System.IO.IOException("(Misc::URLToFileAsync) Error creating or writing to the file named: " + strDestFilename);

    BinaryWriter bw = new BinaryWriter(fs);

    try
    {

        // Call URLToStringAsync() to get the web file as a string first.
        string strFileContents = await URLToStringAsync(strUrl, progress, cancelToken);

        // >>>> NOTE: strFileContents looks correct and is the correct size.

        // Operation cancelled?
        if (!safeCancellationCheck(cancelToken))
        {
            // Note.  BinaryWriter does not have an Async method so we take the hit here
            //  to do a synchronous operation.
            //  See this Stack Overflow post.
            // http://stackoverflow.com/questions/10315316/asynchronous-binaryreader-and-binarywriter-in-net

            // >>>> NOTE: strFileContents.ToCharArray() looks correct and is the correct length.
            bw.Write(strFileContents.ToCharArray(), 0, strFileContents.Length);
        } // if (safeCancellationCheck(cancelToken))
    }
    finally
    {
        // Make sure the file is cleaned up.
        bw.Flush();
        bw.Close();

        // Make sure the file is disposed.
        bw.Dispose();
    } // try/finally

    // >>>> NOTE: output file in Isolated Storage Explorer is the wrong size and contains apparently junk.
} // async public static void URLToFileAsync
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1 回答 1

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您不能将二进制文件下载到字符串中。如您所见，结果将不正确。

请参阅此答案，该答案演示了如何将二进制文件下载到隔离存储：https ://stackoverflow.com/a/6909201/1822514

于 2013-04-09T03:10:54.737 回答