private void EditCommandHandler()
        {
            var vm = new VocabularyItemDialogViewModel(
                (item) => { SaveCommand.Execute(null); }
                );

            vm.Question = VocabularyItem;
            dialogService.ShowDialog(vm, false, "modalDialog");
            RaiseCanExecuteChanged();
        }
        private void AddCommandHandler()
        {
            var question = new VocabularyRecord()
            {
                ShowDateStart = DateTime.Now.Date, ShowDateEnd = DateTime.Now.Date.AddDays(3)
            };
            var vm = new VocabularyItemDialogViewModel(
                (item) => { QuestionList.Add(new VocabularyRecordViewModel(item)); SaveCommand.Execute(null); }
                );

            vm.Question = question;
            dialogService.ShowDialog(vm, false, "modalDialog");
            RaiseCanExecuteChanged();
        }