IsolatedStorage Edit in Windows Phone ScheduledTask - windows-phone-8

Question

I am reading data from IsolatedStorage, but can't edit it in ScheduledTask. How can I edit it?
private void StartToastTask(ScheduledTask task)
{
long rank = 0, difference = 0;
string text = "", nickname = "";
PishtiWCF.PishtiWCFServiceClient ws = ServiceClass.GetPishtiWCFSvc();
ws.GetUsersRankCompleted += (src, e) =>
{
try
{
if (e.Error == null)
{
difference = rank - e.Result.GeneralRank;
if (!String.IsNullOrEmpty(nickname))
{
if (difference < 0)
text = string.Format("{0}, {1} kişi seni geçti!", nickname, difference.ToString(), e.Result.GeneralRank);
else if (difference > 0)
text = string.Format("{0}, {1} kişiyi daha geçtin!", nickname, Math.Abs(difference).ToString(), e.Result.GeneralRank);
else if (e.Result.GeneralRank != 1)
text = string.Format("{0}, sıralamadaki yerin değişmedi!", nickname, e.Result.GeneralRank);
else
text = string.Format("{0}, en büyük sensin, böyle devam!", nickname);
}
else
return;
Mutex mut;
if (!Mutex.TryOpenExisting("IsoStorageMutex", out mut))
mut = new Mutex(false, "IsoStorageMutex");
mut.WaitOne();
using (IsolatedStorageFile file = IsolatedStorageFile.GetUserStoreForApplication())
{
using (IsolatedStorageFileStream stream = file.OpenFile("UserRanks", FileMode.Open, FileAccess.Write))
{
StreamWriter writer = new StreamWriter(stream);
writer.Write(string.Format("{0},{1}", nickname, e.Result.GeneralRank));
writer.Close();
stream.Close();
}
}
mut.ReleaseMutex();
ShellToast toast = new ShellToast();
toast.Title = "Pishti";
toast.Content = text;
toast.Show();
}
FinishTask(task);
}
catch (Exception)
{
}
};
try
{
Mutex mut;
if (!Mutex.TryOpenExisting("IsoStorageMutex", out mut))
mut = new Mutex(false, "IsoStorageMutex");
mut.WaitOne();
using (IsolatedStorageFile file = IsolatedStorageFile.GetUserStoreForApplication())
{
using (IsolatedStorageFileStream stream = file.OpenFile("UserRanks", FileMode.Open, FileAccess.Read))
{
using (StreamReader reader = new StreamReader(stream))
{
string temp = reader.ReadToEnd();
if (temp.Split(',').Count() > 1)
{
nickname = temp.Split(',')[0];
rank = long.Parse(temp.Split(',')[1]);
ws.GetUsersRankAsync(nickname);
}
reader.Close();
}
stream.Close();
}
}
mut.ReleaseMutex();
}
catch (Exception)
{
}
}
I am getting rank from UserRanks file, for example 1200, but when I get and data from WCF, edit it to 1000 and want to write it to IsolatedStorage, It doesn't crash application but it fails.
Do you know why?
Thanks.

Answer 1

I've fixed it with delete file.
Mutex mut;
if (!Mutex.TryOpenExisting("IsoStorageMutex", out mut))
mut = new Mutex(false, "IsoStorageMutex");
mut.WaitOne();
using (IsolatedStorageFile file = IsolatedStorageFile.GetUserStoreForApplication())
{
if (file.FileExists("UserRanks"))
file.DeleteFile("UserRanks");
using (IsolatedStorageFileStream stream = file.OpenFile("UserRanks", FileMode.OpenOrCreate, FileAccess.Write))
{
StreamWriter writer = new StreamWriter(stream);
writer.Write(string.Format("{0},{1}", nickname, e.Result.GeneralRank));
writer.Close();
stream.Close();
}
}
mut.ReleaseMutex();

Answer 2

You appear to write to the file first, which makes sense, but when you do so you use a file access mode - FileMode.Open - which means "open an existing file". The first time you do this the file won't exist and the open will fail.
You should either use FileMode.OpenOrCreate, which is self explanatory, or FileMode.Append which will open the file if it exists and seek to the end of the file, or create a new file if it doesn't.
If you want to throw away any pre-existing file (which is what your delete then create will do) then just use FileMode.Create