WPF中确保显示ListBox选中的Item

WPF中没有提供确保显示ListBox选中的Item这个功能，因此写了个函数来实现：

 

        public void EnsureListBoxItemVisible(ListBox listbox, ListBoxItem selectedItem)
        {

            int itemIndex = listbox.SelectedIndex;

            ScrollViewer scrollViewer = (ScrollViewer)VisualTreeHelper.GetChild(VisualTreeHelper.GetChild(listbox, 0), 0);

            int verticalOffset = (int)scrollViewer.VerticalOffset;
            if (itemIndex < verticalOffset)
            {
                verticalOffset = itemIndex;
            }
            else if (itemIndex > (int)(scrollViewer.ViewportHeight + verticalOffset - 1))
            {
                verticalOffset = itemIndex + 1 - (int)scrollViewer.ViewportHeight;
            }

            if (verticalOffset != scrollViewer.VerticalOffset)
                scrollViewer.ScrollToVerticalOffset(verticalOffset);

        }

 

        private void TestListBox_SelectionChanged(object sender, SelectionChangedEventArgs e)
        {
            Application.Current.Dispatcher.BeginInvoke(new Action(delegate
            {
                ListBoxItem selectedItem = e.OriginalSource as ListBoxItem;

                ViewModel.EnsureListBoxItemVisible(TestListBox, selectedItem);

            }), System.Windows.Threading.DispatcherPriority.ApplicationIdle);
        }

        private void TestListBox_ItemSelected(object sender, RoutedEventArgs e)
        {
            Application.Current.Dispatcher.BeginInvoke(new Action(delegate
            {
                ListBoxItem selectedItem = e.OriginalSource as ListBoxItem;

                ViewModel.EnsureListBoxItemVisible(TestListBox, selectedItem);

            }), System.Windows.Threading.DispatcherPriority.ApplicationIdle);
        }