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.