当向ObservableCollection添加或删除项目时，WP7 UIElement属性绑定到ObservableCollection时未更新

Question

在以下代码中：绑定到ObservableCollection时，绑定到ObservableCollection的某个UIElement在向项目添加或从集合中移除时不会更新。

具体来说：

甲Person对象包括ObservableCollection属性，链接，它可以包含任何数量的可指其它Person对象链接对象。 Person和Link类都实现了INotifyPropertyChanged接口。

public class Person: INotifyPropertyChanged 
{ 
    // INotifyPropertyChanged implementation 
    public event PropertyChangedEventHandler PropertyChanged; 
    private void NotifyPropertyChanged(String info) 
    { 
     if (PropertyChanged != null) 
     { 
      PropertyChanged(this, new PropertyChangedEventArgs(info)); 
     } 
    } 

    // fields 
    private string id = ""; 
    private string firstName = ""; 
    private string lastName = ""; 
    private Links links = new Links(); 

    // properties firing PropertyChanged events 
    public string ID 
    { 
     get { return id; } 
     set 
     { 
      if (value != this.id) 
      { 
       this.id = value; 
       NotifyPropertyChanged("ID"); 
      } 
     } 
    } 
    public string FirstName 
    { 
     get { return firstName; } 
     set 
     { 
      if (value != this.firstName) 
      { 
       this.firstName = value; 
       NotifyPropertyChanged("FirstName"); 
      } 
     } 
    } 
    public string LastName 
    { 
     get { return lastName; } 
     set 
     { 
      if (value != this.lastName) 
      { 
       this.lastName = value; 
       NotifyPropertyChanged("LastName"); 
      } 
     } 
    } 
    public Links Links 
    { 
     get { return links; } 
     set 
     { 
      if (value != this.links) 
      { 
       this.links = value; 
       NotifyPropertyChanged("Links"); 
      } 
     } 
    } 

    // constructors 
    public Person() 
    { 
     new Person("", "", ""); 
    } 
    public Person(string id, string firstName, string lastName) 
    { 
     this.ID = id; 
     this.FirstName = firstName; 
     this.LastName = lastName; 
    } 

} 



public enum LinkState { none, oneway, twoway } 

public class Link: INotifyPropertyChanged 
{ 

    // INotifyPropertyChanged implementation 
    public event PropertyChangedEventHandler PropertyChanged; 
    private void NotifyPropertyChanged(String info) 
    { 
     if (PropertyChanged != null) 
     { 
      PropertyChanged(this, new PropertyChangedEventArgs(info)); 
     } 
    } 

    // fields 
    private Person fromWhom; 
    private Person toWhom; 

    // properties firing PropertyChanged events 
    public Person FromWhom 
    { 
     get { return fromWhom; } 
     set 
     { 
      if (value != this.fromWhom) 
      { 
       this.fromWhom = value; 
       NotifyPropertyChanged("FromWhom"); 
      } 
     } 
    } 
    public Person ToWhom 
    { 
     get { return toWhom; } 
     set 
     { 
      if (value != this.toWhom) 
      { 
       this.toWhom = value; 
       NotifyPropertyChanged("ToWhom"); 
      } 
     } 
    } 

    // constructors 
    public Link() 
    { 
     new Link(null, null); 
    } 
    public Link(Person fromWhom, Person toWhom) 
    { 
     this.FromWhom = fromWhom; 
     this.ToWhom = toWhom; 
    } 

} 

链接和人群类都是ObservableCollections的子类。 Crowd对象是Person对象的ObservableCollection。甲链接目的是链接对象的一个​​ObservableCollection：

public class Links: ObservableCollection<Link> 
    { 

    } 


    public class Crowd : ObservableCollection<Person> 
    { 

    } 

MainPage类的WP7应用的是的PhoneApplicationPage类的子类。 它包含两个属性： Crowd，一个人群对象和 Me，一个Person对象。

以下XAML应该显示： a）从人物对象到人群中的链接数量，以及 b）人群中的人物对象列表。

<phone:PhoneApplicationPage 
    x:Name="ThePage" 
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
    xmlns:phone="clr-namespace:Microsoft.Phone.Controls;assembly=Microsoft.Phone" 
    xmlns:shell="clr-namespace:Microsoft.Phone.Shell;assembly=Microsoft.Phone" 
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
    xmlns:local="clr-namespace:PersonLink" 
    mc:Ignorable="d" d:DesignWidth="480" d:DesignHeight="768" 
    x:Class="PersonLink.MainPage" 
    FontFamily="{StaticResource PhoneFontFamilyNormal}" 
    FontSize="{StaticResource PhoneFontSizeNormal}" 
    Foreground="{StaticResource PhoneForegroundBrush}" 
    SupportedOrientations="Portrait" Orientation="Portrait" 
    shell:SystemTray.IsVisible="True" 
    DataContext="{Binding ElementName=ThePage, Path=Crowd}"> 

    <phone:PhoneApplicationPage.Resources> 
     <local:LinksToCountConverter x:Key="linkCount" /> 
    </phone:PhoneApplicationPage.Resources> 

    <!--LayoutRoot is the root grid where all page content is placed--> 
    <Grid x:Name="LayoutRoot" Background="Transparent"> 
     <Grid.RowDefinitions> 
      <RowDefinition Height="Auto"/> 
      <RowDefinition Height="*"/> 
     </Grid.RowDefinitions> 

     <!--TitlePanel contains the name of the application and page title--> 
     <StackPanel x:Name="TitlePanel" Grid.Row="0" Margin="12,17,0,28"> 
      <TextBlock x:Name="ApplicationTitle" Text="MY APPLICATION" Style="{StaticResource PhoneTextNormalStyle}"/> 
      <TextBlock x:Name="PageTitle" Text="page name" Margin="9,-7,0,0" Style="{StaticResource PhoneTextTitle1Style}"/> 
     </StackPanel> 

     <!--ContentPanel - place additional content here--> 
     <StackPanel x:Name="ContentPanel" Grid.Row="1" Margin="12,0,12,0"> 
      <StackPanel Orientation="Horizontal"> 
       <TextBlock Text="{Binding ElementName=ThePage, Path=Me.FirstName}" /> 
       <TextBlock Text=" has " /> 
       <TextBlock x:Name=LinkCounter Text="{Binding ElementName=ThePage, Path=Me.Links,Converter={StaticResource linkCount}}" /> 
       <TextBlock Text=" links." /> 
      </StackPanel> 
      <ItemsControl ItemsSource="{Binding .}"> 
       <ItemsControl.ItemTemplate> 
        <DataTemplate> 
         <StackPanel Orientation="Horizontal"> 
          <TextBlock Text="{Binding ID}" /> 
          <TextBlock Text=" " /> 
          <TextBlock Text="{Binding FirstName}" /> 
          <TextBlock Text=" " /> 
          <TextBlock Text="{Binding LastName}" /> 
          <local:LinkButton Content="Link" Click="LinkButton_Click"/> 
         </StackPanel> 
        </DataTemplate> 
       </ItemsControl.ItemTemplate> 
      </ItemsControl> 
     </StackPanel> 
    </Grid> 
</phone:PhoneApplicationPage> 

然而，当链接对象中添加或Me.Links（一ObserverableCollection）的文本块名为“LinkCounter”删除不更新，即使它绑定到的ObservableCollection。

由于Me.Links ObservableCollection在添加新链接或更改现有链接时发生更改，因此我认为绑定到它的任何内容都应该更新。

在这个问题上的任何帮助，将不胜感激。 谢谢。

Answer 1

因为您没有更改对Links集的引用，所以不会在这里触发数据绑定。而不是绑定到参考和使用转换器尝试使用

<TextBlock x:Name=LinkCounter Text="{Binding ElementName=ThePage, Path=Me.Links.Count" />