使用 BindlingList 中項屬性的更改更新 ListBox

Question

當我更改 BindingList 中項目的屬性時，盡管基礎 object 已更改，但更改不會傳播到 ListBox。

public class MyClass : INotifyPropertyChanged
{
    public override string ToString()
    {
        return this.Name;
    }

    #region Name

    private string name;

    public string Name
    {
        get
        {
            return this.name;
        }

        set
        {
            if (value == this.name) return;

            this.name = value;
            this.OnPropertyChanged("Name");
        }
    }

    #endregion

    #region INotifyPropertyChanged event

    ///<summary>
    ///Occurs when a property value changes.
    ///</summary>
    public event PropertyChangedEventHandler PropertyChanged;


    /// <summary>
    /// Raises the <see cref="PropertyChanged"/> event for
    /// a given property.
    /// </summary>
    /// <param name="propertyName">The name of the changed property.</param>
    protected void OnPropertyChanged(string propertyName)
    {
        //validate the property name in debug builds
        VerifyProperty(propertyName);

        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }


    /// <summary>
    /// Verifies whether the current class provides a property with a given
    /// name. This method is only invoked in debug builds, and results in
    /// a runtime exception if the <see cref="OnPropertyChanged"/> method
    /// is being invoked with an invalid property name. This may happen if
    /// a property's name was changed but not the parameter of the property's
    /// invocation of <see cref="OnPropertyChanged"/>.
    /// </summary>
    /// <param name="propertyName">The name of the changed property.</param>
    [Conditional("DEBUG")]
    private void VerifyProperty(string propertyName)
    {
        Type type = this.GetType();

        //look for a *public* property with the specified name
        PropertyInfo pi = type.GetProperty(propertyName);
        if (pi == null)
        {
            //there is no matching property - notify the developer
            string msg = "OnPropertyChanged was invoked with invalid property name {0}: ";
            msg += "{0} is not a public property of {1}.";
            msg = String.Format(msg, propertyName, type.FullName);
            Debug.Fail(msg);
        }
    }

    #endregion
}

和 XAML

<Window x:Class="testBL.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <StackPanel>
        <ListBox x:Name="myListBox">
        </ListBox>
        <Button x:Name="changeButton" Click="changeButton_Click">Change an item</Button>
    </StackPanel>
</Window>

Answer 1

因為您將ListBox綁定到集合，所以每個ListBoxItem的默認數據上下文是實例。 例如，集合是ObservableCollection<MyClass> ，每個ListBoxItem的數據上下文是MyClass實例。

由於您沒有提供數據模板，因此ListBoxItem有效地綁定到"{Binding}" ，這會導致調用您的MyClass.ToString()方法。 由於ToString()不是屬性，因此它不支持屬性更改通知。 以這種方式使用綁定（綁定到ToString() ）僅適用於不可變對象。

解決方案是為您的ListBoxItem提供顯式綁定，如下所示：

<ListBox.ItemTemplate>
    <DataTemplate>
        <TextBlock Text="{Binding Name}"/>
    </DataTemplate>
</ListBox.ItemTemplate>

或使您的MyClass object 不可變並替換它們而不是改變它們。

Answer 2

您需要為 BindingList 的 NotifyPropertyChanged 中的每個項目分配一個事件處理程序，並且當發生這種情況時，在事件處理程序中引發一個 CollectionChanged 事件。

我建議使用從 ObservableCollection 繼承並自動分配和刪除處理程序的集合。 我稱其為 VeryObservableCollection。