Error "Operation not permitted on IsolatedStorageFileStream." wp7 - windows-phone-7

Question

I am trying to read a text file from IsolatedStorage and check it contains a string. If not, the string is added to the end of the file. But When I am trying to write the string into file I got an error: "Operation not permitted on IsolatedStorageFileStream.". My code shown below. How can I overcome this problem?
public void AddToDownloadList()
{
IsolatedStorageFile downloadFile=IsolatedStorageFile.GetUserStoreForApplication();
try
{
string downloads = string.Empty;
if (!downloadFile.DirectoryExists("DownloadedFiles"))
downloadFile.CreateDirectory( "DownloadedFiles" );
if(downloadFile.FileExists("DownloadedFiles\\DownloadList.txt"))
{
IsolatedStorageFileStream downloadStream = downloadFile.OpenFile("DownloadedFiles\\DownloadList.txt",FileMode.Open, FileAccess.Read );
using ( StreamReader reader = new StreamReader( downloadStream ) )
{
downloads = reader.ReadToEnd();
reader.Close();
}
downloadFile.DeleteFile( "DownloadedFiles\\DownloadList.txt" );
}
downloadFile.CreateFile( "DownloadedFiles\\DownloadList.txt" );
string currentFile = FileName;
if ( !downloads.Contains( currentFile ) )
{
downloads += currentFile;
using ( StreamWriter writeFile = new StreamWriter( new IsolatedStorageFileStream( "DownloadedFiles\\DownloadList.txt", FileMode.Create, FileAccess.Write, downloadFile ) ) )
{
writeFile.Write( currentFile + "," );
writeFile.Close();
}
}
}
catch ( Exception ex )
{
string message = ex.Message;
}
}

Answer 1

I think the problem you were having has to do with the line where you create the StreamWriter by newing up the IsolatedStorageFileStream - when you already should have the right one from the return of the downloadFile.CreateFile() call.
Try this code, I think it does what you want to do:
public static void AddToDownloadList()
{
try
{
AddToDownloadList("DownloadedFiles", "this file name", "DownloadedFiles\\DownloadList.txt");
}
catch (Exception ex)
{
System.Diagnostics.Debug.WriteLine("Exception: " + ex.Message);
}
}
public static void AddToDownloadList(string directory, string fileName, string filePath)
{
string downloads = string.Empty;
using (IsolatedStorageFile downloadFile = IsolatedStorageFile.GetUserStoreForApplication())
{
if (!downloadFile.DirectoryExists(directory))
downloadFile.CreateDirectory(directory);
if (downloadFile.FileExists(filePath))
{
IsolatedStorageFileStream downloadStream = downloadFile.OpenFile(filePath, FileMode.Open, FileAccess.Read);
using (StreamReader reader = new StreamReader(downloadStream))
{
downloads = reader.ReadToEnd();
reader.Close();
}
}
string currentFile = fileName;
if (!downloads.Contains(currentFile))
{
downloadFile.DeleteFile(filePath);
using (IsolatedStorageFileStream stream = downloadFile.CreateFile(filePath))
{
downloads += currentFile;
using (StreamWriter writeFile = new StreamWriter(stream))
{
writeFile.Write(currentFile + ",");
writeFile.Close();
}
}
}
}
}