private void LoadTagsFromFile()
        {
            if (!System.IO.File.Exists(GetTagsFileName()))
            {
                return;
            }
            XmlSerializer deserializer = new XmlSerializer(typeof(SortedObservableCollection <Tag>));

            using (System.IO.TextReader reader = new System.IO.StreamReader(GetTagsFileName()))
            {
                tags      = (SortedObservableCollection <Tag>)deserializer.Deserialize(reader);
                lastTagID = tags.Max(obj => obj.ID);
            }
        }