Question

I’m trying to add support for tracking application usage to a WP7 app (e.g., how many times has the app been run, including wakeups from tombstoning). I thought I was doing this in a pretty straight-forward way, but I’m frequently getting IsolatedStorageExceptions, and I’m kind of at a loss for debugging it at the moment.

Paraphrasing from my App.xaml.cs

private void HandleAppCounter() {
  int i = 0;
  settings.TryGetValue<int>("usage", out i);
  i++;

  settings["usage"] = i;
  settings.Save();
}

I call this function when the app is launching or activating. The thing is, it works just fine. But the thing is, if I make another call to isolated storage soon after then that is what blows up. And furthermore, it seems to only blow up if the next call happens pretty soon after.. although I’m having trouble understanding that as well.

The next action performed is usually a user clicking an item in a list. If it happens immediately when it’s displayed, I get a crash from isolated storage. If the user waits a few seconds after the app is launched and then clicks it, there is no crash.

If the above code in HandleAppCounter() is commented out, then the user can click either immediately or later and it never crashes.

Can anyone give me some tips on how to debug this? I’m kind of running into a wall here.

Answer 1

I would suggest stepping away from your custom implementation for a sec and try the same behaviour with the default IsolatedStorageSettings class, if it is still a problem then you should report it to Microsoft Connect site as a bug, otherwise there is some kind of an error in your settings class.

If you’re using IsolatedStorageSettings you might want to make sure, that whenever you’re querying/adding a key, the key is there, if not you must create it.

If you’re using IsolatedStorage filesystem then make sure you are always closing the streams when you’re reading/writing. If you don’t you will get absurd exceptions.