如何从Windows Phone 7中的IsolatedStorageFileStream加载时System.OutOfMemoryException？

Question

我有一个应用程序，它将某些文件存储在独立存储中，并且在文件打开时需要解密。我试图将IsolatedStorageFileStream加载到一个字节数组中并启动AES256解密。当文件大小很小时，它工作正常。但是，当文件大小很大时（比如说大约120MB），它会抛出System.OutOfMemoryException。以下是我的部分代码：

     IsolatedStorageFileStream m_rawStream = 
         IsolatedStorageFile.GetUserStoreForApplication().OpenFile("shared\\transfers\\" + 
         DownloadFileName, FileMode.OpenOrCreate, FileAccess.ReadWrite); 


        byte[] m_rawByte = new byte[_totalByte]; 
        m_rawStream.Read(m_rawByte, 0, _totalByte); 
        m_rawStream.Close(); 

        //Decrypte downloaded epub 
        byte[] m_decryptedBytes = _decryptStringFromBytesAES(m_rawByte, 
           _hexStringToByteArray(_decryptKey), 
           _hexStringToByteArray(_decryptIV)); 

        //Store on the upper layer of isolated storage 
        using (var isfs = new IsolatedStorageFileStream(DownloadFileName, 
             FileMode.Create, 
             IsolatedStorageFile.GetUserStoreForApplication())) 
        { 
         isfs.Write(m_decryptedBytes, 0, m_decryptedBytes.Length); 
         isfs.Flush(); 
        } 

//AES Decrypt helper 
    private byte[] _decryptStringFromBytesAES(byte[] cipherText, byte[] Key, byte[] IV) 
    { 
     // TDeclare the streams used 
     // to decrypt to an in memory 
     // array of bytes. 
     MemoryStream msDecrypt = null; 
     CryptoStream csDecrypt = null; 

     // Declare the RijndaelManaged object 
     // used to decrypt the data. 
     AesManaged aesAlg = null; 

     // Declare the byte[] used to hold 
     // the decrypted byte. 
     byte[] resultBytes = null; 

     try 
     { 
      // Create a RijndaelManaged object 
      // with the specified key and IV. 
      aesAlg = new AesManaged(); 
      aesAlg.KeySize = 256; 
      aesAlg.Key = Key; 
      aesAlg.IV = IV; 

      // Create a decrytor to perform the stream transform. 
      ICryptoTransform decryptor = aesAlg.CreateDecryptor(aesAlg.Key, aesAlg.IV); 

      // Create the streams used for decryption. 
      msDecrypt = new MemoryStream(); 
      csDecrypt = new CryptoStream(msDecrypt, decryptor, CryptoStreamMode.Write); 

      // Read the decrypted bytes from the decrypting stream 
      // and place them in a string. 
      csDecrypt.Write(cipherText, 0, cipherText.Length); 
      //csDecrypt.FlushFinalBlock(); 
      resultBytes = msDecrypt.ToArray(); 
     } 
     catch (Exception e) 
     { 
      Debug.WriteLine(e.Message); 
      MessageBoxResult _result = MessageBox.Show("無法開啟檔案，請重試或聯絡技術人員。", "錯誤", MessageBoxButton.OK); 
      if (_result == MessageBoxResult.OK) 
      { 
       new SimpleNavigationService().Navigate("/View/MainPange.xaml"); 
      } 
     } 

     return resultBytes; 

    } 

如何避免获得OutOfMemory异常？谢谢。

Answer 1

它看起来像是将整个加密文件加载到内存中 - 如果这是120MB，则需要大量内存。

您应该找到一种加载和解密文件的方法，该文件以较小的数据块读取和解密数据。