private async void createLogFileAsync()
{
Windows.Storage.StorageFolder storageFolder =
Windows.Storage.ApplicationData.Current.LocalFolder;
var messageDialog = new MessageDialog(storageFolder.ToString());
Windows.Storage.StorageFile sampleFile =
await storageFolder.CreateFileAsync("log.txt",
Windows.Storage.CreationCollisionOption.GenerateUniqueName);
stream = await sampleFile.OpenAsync(Windows.Storage.FileAccessMode.ReadWrite);
outputStream = stream.GetOutputStreamAt(0);
dataWriter = new Windows.Storage.Streams.DataWriter(outputStream);
}