Windows Phone 7：使ListBox項目動態更改

Question

我正在創建一個Windows Phone應用程序，該應用程序將播放從列表中選擇的一系列聲音片段。我正在使用MVVM（模型視圖視圖模型）設計模式，併爲我的數據設計了一個模型，以及我的頁面的視圖模型。以下是對ListBox中的XAML看起來像：

<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> 

我的問題是這樣的：我希望能夠展開和摺疊ListBox中的項目的一部分。正如你所看到的，我對可見性有約束力。該綁定來自MediaModel。但是，當我在ObservableCollection中更改此屬性時，頁面不會更新以反映此情況。

視圖模型這個頁面看起來像這樣：

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)); 
     } 
    } 
} 

的綁定正常工作，我看到顯示的數據;但是，當我更改屬性時，列表不會更新。我相信這可能是因爲當我更改可觀察集合中的內容時，屬性更改事件不會觸發。

我該怎麼做才能解決這個問題？我對此有所瞭解，但許多教程並未涵蓋此類行爲。任何幫助將不勝感激！

感謝

編輯：按照要求，我已經添加了MediaModel代碼：

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)); 
     } 
    } 
} 

本來我沒有這個類實現INotifyPropertyChanged。我做了這件事，看看它是否能解決問題。我希望這可能只是一個數據對象。

Answer 1

試着改變你長的描述可見性屬性來這看看能否解決

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

如果它作出的簡短描述屬性相同的變化。