ListBox 数据绑定未正确更新

Question

我得到一个奇怪的结果，当绑定到 ObservableCollection 的数据绑定到 ListBox 时，它会在视图模型构造函数中填充，但当我将相同的 ObservableCollection 填充代码移动到 @ 时不会987654324@ 事件（从视图上的事件处理程序后面的代码和 RoutedCommand 尝试）。没有async 网络服务或后台线程。

当我单步执行代码时，视图模型中的ObservableCollection 在从按钮事件调用时仍会填充，但ListBox 上的数据不会更新。两者的 XAML 相同。

这里有一些代码：

XAML

                <ListBox ItemsSource="{Binding Books}" BorderBrush="{x:Null}" Name="Results">
                <ListBox.ItemTemplate>
                    <DataTemplate>
                        <StackPanel Orientation="Vertical">
                            <TextBlock Text="{Binding Title}" FontSize="12" FontWeight="Bold" />
                            <TextBlock Text="{Binding ID}" FontSize="10" FontStyle="Italic" />
                        </StackPanel>
                    </DataTemplate>
                </ListBox.ItemTemplate>
            </ListBox>
       ...
            <Button Command="{x:Static commands:BookQueryCommands.Query}" Content="Search" Width="119" Height="30" HorizontalAlignment="Right" VerticalAlignment="Bottom" Margin="0,25,0,0"/>

查看后面的代码

public partial class BookExplorer : UserControl
{
    private BookExplorerViewModel vm;

    public BookExplorer()
    {
        this.InitializeComponent();

        vm = new BookExplorerViewModel();
        this.DataContext = vm;

        this.CommandBindings.Add(new CommandBinding(BookQueryCommands.Query, ExecuteQuery));
    }

    public void ExecuteQuery(object sender, ExecutedRoutedEventArgs e) {
        vm.ExecuteBookQuery();
    }
}

视图模型

    public class BookExplorerViewModel : DependencyObject
{   
    private IBookListProvider bookProvider;
    private bool canQuery = true;

    public ObservableCollection<BookModel> Books { get; set; }
    public string Title { get; set; }
    public string ID { get; set; }
    public DateTime LastModifiedDate { get; set; }

    public BookExplorerViewModel() {
        bookProvider = new BookListProvider();
    }

    public void ExecuteBookQuery() {
        Books = bookProvider.DocumentsQuery("temp");
    }
}

// bookProvider.DocumentsQuery("temp") just fills with dummy data.
// Binding works fine if the code in ExecuteBookQuery() is in the VM constructor
// Books is still populated fine in either case just binding is not updated

型号

public class BookModel : INotifyPropertyChanged
{
    private string title;
    public string Title {
        get { return title; }
        set {
            if (value != this.title) {
                this.title = value;
                NotifyPropertyChanged(Title);
            }
        }
    }

    private string id;
    public string ID {
        get { return id; }
        set {
            if (value != this.id) {
                this.id = value;
                NotifyPropertyChanged(ID);
            }
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;

    private void NotifyPropertyChanged(String info) {
        if (PropertyChanged != null) {
            PropertyChanged(this, new PropertyChangedEventArgs(info));
        }
    }
}

Answer 1

视图模型中的 Books 属性设置器不会触发 PropertyChanged 并且您正在绑定到它，不是吗？当您将对象分配给Books 属性时，视图会绑定到它。当您将其他内容分配给 Books 时，它是一个完全不同的对象，并且 View 不知道它，除非您触发一个表明绑定应该重新连接到这个新集合的事件。

Answer 2

我将视图模型更改为：

public class BookExplorerViewModel : DependencyObject
{   
    private IBookListProvider bookProvider;
    private bool canQuery = true;

    public ObservableCollection<BookModel> Books { get; set; }
    public string Title { get; set; }
    public string ID { get; set; }
    public DateTime LastModifiedDate { get; set; }

    public BookExplorerViewModel() {
        bookProvider = new BookListProvider();            
        Books = new ObservableCollection<BookModel>(); 
    }

    public void ExecuteBookQuery() {
        Books.Clear();

        foreach(BookModel book in bookProvider.DocumentsQuery("temp")){
            Books.Add(book);
        }
    }
}

现在可以正常使用了。