async void DoTestUsernameCommand()
{
try
{
bool exists = await _mLearningService.CheckIfExists <User>(usr => usr.username == Username, (it) => it.updated_at, it => it.id);
IsUsernameValid = !exists;
}
catch (WebException e)
{
ConnectionOK = false;
}
catch (MobileServiceInvalidOperationException ex)
{
OperationOK = false;
}
}