[英]How do you bind an observable collection to a listview located in a modal/window?
[英]How to bind an Observable Collection to a ListView
在此示例之后,我已經設置了ListView的綁定, 綁定到可觀察的集合,但是當我運行應用程序時,集合值未顯示在ListView中。
輸出窗口不會引發任何綁定錯誤,因此不確定綁定錯誤可能是什么。 另外,我在列表上設置了一個斷點,然后將其發送到第二個VM並進行填充,即不為null。
我的猜測是,該列表在第二個VM中為空,因為它在傳遞后沒有正確初始化。
誰能建議如何調試ListView為空?
這是在視圖中設置的綁定:
<ListBox ItemsSource="{Binding AddedSubjectGradePairsCopy}" Height="400" Margin="0,0,0,-329" VerticalAlignment="Top">
<ListBox.ItemTemplate>
<DataTemplate>
<TextBlock>
<Run Text="{Binding Subject}" /><Run Text=" - " /><Run Text="{Binding Points}" />
</TextBlock>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
視圖的數據上下文在后面的代碼中設置如下:
namespace LC_Points.View
{
/// <summary>
/// An empty page that can be used on its own or navigated to within a Frame.
/// </summary>
public sealed partial class ViewSubjectGradePage : Page
{
private NavigationHelper navigationHelper;
private ViewSubjectGradeViewModel ViewModel;
public ViewSubjectGradePage()
{
this.InitializeComponent();
this.navigationHelper = new NavigationHelper(this);
this.navigationHelper.LoadState += this.NavigationHelper_LoadState;
this.navigationHelper.SaveState += this.NavigationHelper_SaveState;
ViewModel = new ViewSubjectGradeViewModel();
this.DataContext = ViewModel;
}
/// <summary>
/// Gets the <see cref="NavigationHelper"/> associated with this <see cref="Page"/>.
/// </summary>
public NavigationHelper NavigationHelper
{
get { return this.navigationHelper; }
}
/// <summary>
/// Populates the page with content passed during navigation. Any saved state is also
/// provided when recreating a page from a prior session.
/// </summary>
/// <param name="sender">
/// The source of the event; typically <see cref="NavigationHelper"/>
/// </param>
/// <param name="e">Event data that provides both the navigation parameter passed to
/// <see cref="Frame.Navigate(Type, Object)"/> when this page was initially requested and
/// a dictionary of state preserved by this page during an earlier
/// session. The state will be null the first time a page is visited.</param>
private void NavigationHelper_LoadState(object sender, LoadStateEventArgs e)
{
}
/// <summary>
/// Preserves state associated with this page in case the application is suspended or the
/// page is discarded from the navigation cache. Values must conform to the serialization
/// requirements of <see cref="SuspensionManager.SessionState"/>.
/// </summary>
/// <param name="sender">The source of the event; typically <see cref="NavigationHelper"/></param>
/// <param name="e">Event data that provides an empty dictionary to be populated with
/// serializable state.</param>
private void NavigationHelper_SaveState(object sender, SaveStateEventArgs e)
{
}
#region NavigationHelper registration
/// <summary>
/// The methods provided in this section are simply used to allow
/// NavigationHelper to respond to the page's navigation methods.
/// <para>
/// Page specific logic should be placed in event handlers for the
/// <see cref="NavigationHelper.LoadState"/>
/// and <see cref="NavigationHelper.SaveState"/>.
/// The navigation parameter is available in the LoadState method
/// in addition to page state preserved during an earlier session.
/// </para>
/// </summary>
/// <param name="e">Provides data for navigation methods and event
/// handlers that cannot cancel the navigation request.</param>
protected override void OnNavigatedTo(NavigationEventArgs e)
{
this.navigationHelper.OnNavigatedTo(e);
}
protected override void OnNavigatedFrom(NavigationEventArgs e)
{
this.navigationHelper.OnNavigatedFrom(e);
}
#endregion
}
}
並通過構造函數在ViewSubjectGradeVM中接收列表:
namespace LC_Points.ViewModel
{
public class ViewSubjectGradeViewModel
{
public ViewSubjectGradeViewModel()
{
}
/// <summary>
/// Initializes a new instance of the ViewSubjectGradeViewModel class.
/// </summary>
public ViewSubjectGradeViewModel(IEnumerable<ScoreModel> addedSubjectGradePairs)
{
this.AddedSubjectGradePairsCopy = addedSubjectGradePairs;
}
//Property for collection passed from MainViewModel
public IEnumerable<ScoreModel> AddedSubjectGradePairsCopy { get; set; }
}
}
這是從MainVM傳遞到ViewSubjectGradeVM的List的支持模型:
namespace LC_Points.Model
{
public class ScoreModel : INotifyPropertyChanged
{
// The name of the subject.
public string Subject { get; set; }
// The points paired with each grade type.
public int Points { get; set; }
public event PropertyChangedEventHandler PropertyChanged;
private void RaisePropertyChanged(string propertyName)
{
if (this.PropertyChanged != null)
{
this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
}
}
嘗試這樣的事情。 當然,您的模型應該來自某些源,您應該將其映射到視圖模型。 但這說明了設置正確的數據上下文的方法。
var scoremodels = new List<ScoreModel>
{
new ScoreModel {Subject = "Subj1", Points = 6},
new ScoreModel {Subject = "Subj2", Points = 3},
new ScoreModel {Subject = "Subj3", Points = 8},
}
ViewModel = new ViewSubjectGradeViewModel(scoreModels);
this.DataContext = ViewModel;
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