private void OnSelectionChanged()
        {
            if (this.SelectedItems != null && this.SelectedItems.Count > 0)
            {
                if (this.GalleryItems != null)
                {
                    foreach (var item in this.GalleryItems)
                    {
                        item.IsSelected = false;
                    }
                }

                this.selectedItem = (GalleryItemViewModelBase)this.SelectedItems.First();

                this.selectedItem.IsSelected = true;
            }
        }
        private void OnSelectedItemsCollectionChanged()
        {
            if (this.SelectedItems != null)
            {
                this.SelectedItems.CollectionChanged += this.SelectedItems_CollectionChanged;

                if (this.SelectedItems != null)
                {
                    if (this.SelectedItems.Count == 0)
                    {
                        this.SelectedItems.Add(this.GalleryItems.First());
                    }

                    this.selectedItem = (GalleryItemViewModelBase)this.SelectedItems.First();
                }
            }

            this.OnSelectionChanged();
        }