private async void btnSave_Click(object sender, RoutedEventArgs e)
        {
            var tagDataService = new TagDataService(new EntityFramework.TimetableManagerDbContext());

            if (textBoxtag.Text != "")
            {
                if (isEditState)
                {
                    tag.TagName = textBoxtag.Text;
                    await tagDataService.UpdateTag(tag, tag.TagId);

                    isEditState = false;
                }
                else
                {
                    Tag newTag = new Tag
                    {
                        TagName = textBoxtag.Text
                    };
                    await tagDataService.AddTag(newTag);
                }
                textBoxtag.Clear();
            }
            else
            {
                MessageBox.Show("Insert a Tag!!");
            }

            TagDataList.Clear();
            _ = load();
        }