Windows Phone 7:使ListBox项动态更改 [英] Windows Phone 7: Making ListBox items change dynamically
问题描述
我正在创建一个Windows Phone应用，该应用将播放从列表中选择的一系列声音片段.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，并为我的页面设计了一个视图模型.这是ListBox的XAML外观:
I am working on creating a Windows Phone app that will play a series of sound clips selected from a list. I am using the MVVM (Model View View-Model) Design pattern and have designed a model for my data, along with a view model for my page. Here is what the XAML for the ListBox looks like:
<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:我希望能够扩展和折叠ListBox中的部分项目.如您所见，我对可见性具有约束力.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此情况.
My question is this: I want to be able to expand and collapse part of the items in the ListBox. As you can see, I have a binding for the visibility. That binding is coming from the MediaModel. However, when I change this property in the ObservableCollection, the page is not updated to reflect this.
此页面的ViewModel如下:
The ViewModel for this page looks like this:
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));
}
}
}
绑定正常工作，并且我看到的是显示的数据；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.
The bindings work correctly and I am seeing the data displayed; however, when I change the properties, the list does not update. I believe that this may be because when I change things inside the observable collection, the property changed event is not firing.
该如何解决?我四处寻找有关此问题的信息，但是许多教程并未涵盖这种行为.任何帮助将不胜感激！
What can I do to remedy this? I have poked around for some info on this, but many of the tutorials don't cover this kind of behavior. Any help would be greatly appreciated!
谢谢
根据要求，我添加了MediaModel代码:
As requested, I have added the MediaModel code:
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，我没有此类实现INotifyPropertyChanged.我这样做是为了看看是否可以解决问题.我希望这可能只是一个数据对象.
Originally, I did not have this class implement the INotifyPropertyChanged. I did this to see if it would solve the problem. I was hoping this could just be a data object.
推荐答案
尝试将您的详细描述可见性属性更改为此，以查看是否可以解决该问题
Try changing your long description visibility property to this to see if that fixes it
private Visibility _longDescriptionVisibility;
public Visibility LongDescriptionVisibility
{
get { return _longDescriptionVisibility; }
set
{
_longDescriptionVisibility = value;
NotifyPropertyChanged("LongDescriptionVisibility");
}
}
如果确实对简短描述属性进行了相同的更改.
If it does make the same change to the short description property.
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