如何在wp8中突出显示ListBox SelectedItem？

Question

友

我正在使用MVVM绑定ListBox SelectedItem，但似乎它不起作用。该列表已成功绑定，但未选择任何项目。

XAML Page

<ListBox x:Name="lsbReadingChapter" SelectedItem="{Binding SelectedItem, Mode=TwoWay}"
ItemsSource="{Binding QuranText}" Style="{StaticResource ListBoxStyle1}"
Grid.Row="1">
 ....
</ListBox>

MVVM代码

public class QuranTextViewModel : INotifyPropertyChanged
    {
        DataSource ds = null;
        ObservableCollection<ArabicTextWithTranslation> _quranText;
        public QuranTextViewModel(Chapter c)
        {
            ds = new DataSource();
            QuranText = new ObservableCollection<ArabicTextWithTranslation>();

            List<ArabicTextWithTranslation> texts = ds.getArabicTextWithTranslation(c);
            Recent r = DataSource.Recents;
            SelectedItem = (from grp in texts
                            where grp.ArabicText.ChapterID == r.ChapterID && grp.ArabicText.AyaID == r.AyaID
                            select grp).FirstOrDefault();
            foreach (ArabicTextWithTranslation t in texts)
            {
                QuranText.Add(t);
            }

        }
        public ObservableCollection<ArabicTextWithTranslation> QuranText
        {
            get { return _quranText; }
            set
            {
                if (_quranText != value)
                {
                    _quranText = value;
                    OnPropertyChanged("QuranText");
                }
            }
        }
        ArabicTextWithTranslation _selectedItem;
        public ArabicTextWithTranslation SelectedItem
        {
            get {
                return _selectedItem; 
            }
            set
            {
                if (_selectedItem != value)
                {
                    _selectedItem = value;
                    OnPropertyChanged("SelectedItem");
                }
            }
        }
}

SelectedItem无效，但在调试模式下，我可以看到SelectedItem中的值。

如何设置SelectedItem和Highlight SelectedItem？