Windows Phone 7：使 ListBox 项目动态变化

Question

我正在创建一个 Windows Phone 应用程序，它将播放从列表中选择的一系列声音剪辑。我正在使用 MVVM（模型视图视图模型）设计模式，并为我的数据设计了一个模型，以及为我的页面设计了一个视图模型。 ListBox 的 XAML 如下所示：

<ListBox x:Name="MediaListBox" Margin="0,0,-12,0" ItemsSource="{Binding Media}" SelectionChanged="MediaListBox_SelectionChanged" HorizontalContentAlignment="Stretch" VerticalContentAlignment="Stretch">

                <ListBox.ItemTemplate >
                    <DataTemplate>
                        <StackPanel Margin="0,0,0,17" Width="432" Orientation="Horizontal">
                            <Image Source="../Media/Images/play.png" />
                            <StackPanel >
                                <TextBlock Text="{Binding Title}" TextWrapping="Wrap" Style="{StaticResource PhoneTextExtraLargeStyle}"/>
                                <TextBlock Text="{Binding ShortDescription}" TextWrapping="Wrap" Margin="12,-6,12,0" Visibility="{Binding ShortDescriptionVisibility}" Style="{StaticResource PhoneTextSubtleStyle}"/>
                                <TextBlock Text="{Binding LongDescription}" TextWrapping="Wrap" Visibility="{Binding LongDescriptionVisibility}" />
                                <StackPanel>
                                    <Slider HorizontalContentAlignment="Stretch" VerticalContentAlignment="Stretch" Visibility="{Binding LongDescriptionVisibility}" ValueChanged="Slider_ValueChanged" LargeChange="0.25" SmallChange="0.05" />
                                </StackPanel>
                            </StackPanel>
                        </StackPanel>
                    </DataTemplate>
                </ListBox.ItemTemplate>
            </ListBox>

我的问题是：我希望能够展开和折叠 ListBox 中的部分项目。如您所见，我有一个可见性绑定。该绑定来自 MediaModel。但是，当我在 ObservableCollection 中更改此属性时，页面不会更新以反映这一点。

此页面的 ViewModel 如下所示：

public class ListenPageViewModel : INotifyPropertyChanged
{
    public ListenPageViewModel()
    {
        this.Media = new ObservableCollection<MediaModel>;

    }

    /// <summary>
    /// A collection for MediaModel objects.
    /// </summary>
    public ObservableCollection<MediaModel> Media { get; private set; }

    public bool IsDataLoaded { get; private set; }

    /// <summary>
    /// Creates and adds the media to their respective collections.
    /// </summary>
    public void LoadData()
    {
        this.Media.Clear();
        this.Media.Add(new MediaModel()
        {
            Title = "Media 1",
            ShortDescription = "Short here.",
            LongDescription = "Long here.",
            MediaSource = "/Media/test.mp3",
            LongDescriptionVisibility = Visibility.Collapsed,
            ShortDescriptionVisibility = Visibility.Visible
        });

        this.Media.Add(new MediaModel()
        {
            Title = "Media 2",
            ShortDescription = "Short here.",
            LongDescription = "Long here.",
            MediaSource = "/Media/test2.mp3",
            LongDescriptionVisibility = Visibility.Collapsed,
            ShortDescriptionVisibility = Visibility.Visible
        });

        this.IsDataLoaded = true;
    }

    public event PropertyChangedEventHandler PropertyChanged;
    private void NotifyPropertyChanged(String propertyName)
    {
        PropertyChangedEventHandler handler = PropertyChanged;
        if (null != handler)
        {
            handler(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

绑定工作正常，我看到显示的数据；但是，当我更改属性时，列表不会更新。我相信这可能是因为当我更改可观察集合中的内容时，属性更改事件没有触发。

我能做些什么来解决这个问题？我已经四处寻找有关此的一些信息，但是许多教程并未涵盖这种行为。任何帮助将不胜感激！

谢谢

编辑：根据要求，我添加了 MediaModel 代码：

    public class MediaModel : INotifyPropertyChanged
{
    public string Title { get; set; }
    public string ShortDescription { get; set; }
    public string LongDescription { get; set; }
    public string MediaSource { get; set; }
    public Visibility LongDescriptionVisibility { get; set; }
    public Visibility ShortDescriptionVisibility { get; set; }

    public MediaModel()
    {
    }

    public MediaModel(string Title, string ShortDescription, string LongDescription, string MediaSource, Visibility LongDescriptionVisibility, Visibility ShortDescriptionVisibility)
    {
        this.Title = Title;
        this.ShortDescription = ShortDescription;
        this.LongDescription = LongDescription;
        this.MediaSource = MediaSource;
        this.LongDescriptionVisibility = LongDescriptionVisibility;
        this.ShortDescriptionVisibility = ShortDescriptionVisibility;
    }
    public event PropertyChangedEventHandler PropertyChanged;
    private void NotifyPropertyChanged(String propertyName)
    {
        PropertyChangedEventHandler handler = PropertyChanged;
        if (null != handler)
        {
            handler(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

最初，我没有让这个类实现INotifyPropertyChanged。我这样做是为了看看它是否能解决问题。我希望这可能只是一个数据对象。

Answer 1

尝试将您的长描述可见性属性更改为此，看看是否可以解决它

private Visibility _longDescriptionVisibility;
public Visibility LongDescriptionVisibility
{
    get { return _longDescriptionVisibility; }
    set
    {
        _longDescriptionVisibility = value;
        NotifyPropertyChanged("LongDescriptionVisibility");
    }
}       

如果它确实对简短描述属性进行了相同的更改。