Operation not permitted on IsolatedStorageFileStream - exception

Question

I'm building this WP7 app that uses a video game API to get the statistics of someone's character (just to help learn silverlight). It grabs the players details from the web service and stores them on isolated storage on the phone to relieve strain from the server.
Originally I had a class which had both the cache writing and reading function, but now i've had to seperate it out into two seperate classes. The cache writing class doesn't matter at the moment, just the cache reading class.
On line 7, it throws an exception saying "Operation not permitted on IsolatedStorageFileStream.", but only during the second time it instantiates the class. I've done some checking with debug and it says the file definately exists, but it stops after the second using clause.
Can anyone help me with this please? I feel like I'm missing something really obvious.
public class CacheReader
{
public PlayerData GetPlayerData(string gamertagIn)
{
using (IsolatedStorageFile CachedReachData = IsolatedStorageFile.GetUserStoreForApplication())
{
using (IsolatedStorageFileStream stream = CachedReachData.OpenFile(gamertagIn + ".xml", FileMode.Open))
{
Debug.WriteLine("Data Retrieved from cache");
XmlSerializer serializer = new XmlSerializer(typeof(PlayerData));
PlayerData loadedPlayer = (PlayerData)serializer.Deserialize(stream);
return loadedPlayer;
}
}
}
}
[EDIT 1]
This is the stack trace i get:
at System.IO.IsolatedStorage.IsolatedStorageFileStream..ctor(String path, FileMode mode, FileAccess access, FileShare share, Int32 bufferSize, IsolatedStorageFile isf)
at System.IO.IsolatedStorage.IsolatedStorageFileStream..ctor(String path, FileMode mode, FileAccess access, IsolatedStorageFile isf)
at System.IO.IsolatedStorage.IsolatedStorageFile.OpenFile(String path, FileMode mode, FileAccess access)
at ReachPhoneApp.CacheReader.GetPlayerFromCache(String gamertagIn)
at ReachPhoneApp.Page2.GetPlayerData()
at ReachPhoneApp.Page2.cacheWriter_UpdateComplete()
at ReachPhoneApp.CacheWriter.WritePlayerDataToCache(String fileNameIn, Object objectIn)
at ReachPhoneApp.CacheWriter.client_GetGameHistoryCompleted(Object sender, GetGameHistoryCompletedEventArgs e)
at ReachPhoneApp.ReachAPI.ReachApiSoapClient.OnGetGameHistoryCompleted(Object state)
at System.Reflection.RuntimeMethodInfo.InternalInvoke(RuntimeMethodInfo rtmi, Object obj, BindingFlags invokeAttr, Binder binder, Object parameters, CultureInfo culture, Boolean isBinderDefault, Assembly caller, Boolean verifyAccess, StackCrawlMark& stackMark)
at System.Reflection.RuntimeMethodInfo.InternalInvoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture, StackCrawlMark& stackMark)
at System.Reflection.MethodBase.Invoke(Object obj, Object[] parameters)
at System.Delegate.DynamicInvokeOne(Object[] args)
at System.MulticastDelegate.DynamicInvokeImpl(Object[] args)
at System.Delegate.DynamicInvoke(Object[] args)
at System.Windows.Threading.DispatcherOperation.Invoke()
at System.Windows.Threading.Dispatcher.Dispatch(DispatcherPriority priority)
at System.Windows.Threading.Dispatcher.OnInvoke(Object context)
at System.Windows.Hosting.CallbackCookie.Invoke(Object[] args)
at System.Windows.Hosting.DelegateWrapper.InternalInvoke(Object[] args)
at System.Windows.RuntimeHost.ManagedHost.InvokeDelegate(IntPtr pHandle, Int32 nParamCount, ScriptParam[] pParams, ScriptParam& pResult)

Answer 1

Check that you don't somehow have two threads accessing IsolatedStorage at the same time (ie. in VS Debug.View.Threads and verify that at the time of the exception you don't have multiple paths through the same IsoStore code).
This happened in my WP7 code once every few days and was tricky to find, as it seemed to occur only when not connectected to the debugger.

Answer 2

You need to call:
stream.Close();
before
return loadedPlayer;

Answer 3

I think the problem is that you didn't specify that multiple threads could read/write at the same time by specifying a System.IO.FileShare.ReadWrite or whatever access you need as the last parameter of OpenFile.
See the discussion here on the Microsoft Forums.

Answer 4

I ran into this issue as well, but for completely different reasons as mentioned above. I hadn't created the directory that I was saving into.
private void SaveStringDataToStorage(string sDirectory, string sFileName, string sFileContent)
{
string sPath;
//
using (IsolatedStorageFile oFile = solatedStorageFile.GetUserStoreForApplication())
{
if (!oFile.DirectoryExists(sDirectory))
oFile.CreateDirectory(sDirectory);
//
sPath = Path.Combine(sDirectory, sFileName);
//
using (var oWriter = new StreamWriter(new IsolatedStorageFileStream(sPath, FileMode.Create, oFile)))
oWriter.Write(sFileContent);
}
}
Using this code will work if you had the same problem as me, plus it's pretty simple so you can adapt it to whatever you need. I was using this code before I had issues, but I'd forgotten the ! so the directory was never created haha. Just typical. Hope this helps :)
EDIT
Looking closer at the original question, it may be that the file didn't exist. I think it's always best to do IsolatedStorageFile.DirectoryExists() and IsolatedStorageFile.FileExists() before trying to access either location, whether you are reading or writing.

Answer 5

By default when you use IsolatedStorageFile.OpenFile("filename", FileMode.Open) your file gets locked by this thread and no other thread would be able to access this file until 1st thread close it. But if you like to share your file in multiple threads for read purpose only then I would recommend you to use following override
IsolatedStorageFile.OpenFile("filename", FileMode.Open, FileAccess.Read, FileShare.Read)
see details here