private void AddSourceBtn_Click(object sender, RoutedEventArgs e)
        {
            SourceWindow window = new SourceWindow();

            window.Owner = this;
            window.Title = "Add new source";
            if (window.ShowDialog() == true)
            {
                sources.Add(window.SourceResult);
            }
        }
        private void EditSourceBtn_Click(object sender, RoutedEventArgs e)
        {
            if (SelectSourceCombo.SelectedValue == null)
            {
                return;
            }

            Source       source = (Source)SelectSourceCombo.SelectedValue;
            SourceWindow window = new SourceWindow(source);

            window.Owner = this;
            window.Title = "Edit source";
            if (window.ShowDialog() == true)
            {
                //replace the Source with the result one from SourceWindow
                int index = sources.IndexOf(source);
                sources[index] = window.SourceResult;
                SelectSourceCombo.SelectedItem = window.SourceResult;
            }
        }