PropertyChanged is ignored when Binding to IEnumerable where reference stays the same

问题

I created a minimal example to illustrate the binding issue. IEnumerable<string> NewReference gets updated as expected. IEnumerable<string> SameReference is not updated, presumably because the reference is the same. Raise("SameReference"); was not enough to make WPF update the reference.

Is there something that can be done to make the WPF framework revaluate SameReference even though it has the same reference?

xaml:

<Window x:Class="Stackoverflow.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">
    <Grid Background="Azure">
        <Grid.RowDefinitions>
            <RowDefinition Height="5*"/>
            <RowDefinition Height="1*"/>
        </Grid.RowDefinitions>
        <Grid.ColumnDefinitions>
            <ColumnDefinition/>
            <ColumnDefinition/>
        </Grid.ColumnDefinitions>
        <Button Content="Update" Margin="5" Grid.Row="1" Grid.ColumnSpan="2" Click="Button_Click" />
        <ListBox ItemsSource="{Binding SameReference}" Margin="5" />
        <ListBox ItemsSource="{Binding NewReference}" Margin="5" Grid.Column="1" />
    </Grid>
</Window>

xaml.cs:

using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.ComponentModel;
using System.Windows;
using System.Windows.Controls;

namespace Stackoverflow
{
    public partial class MainWindow : Window , INotifyPropertyChanged
    {
        public List<string> data = new List<string> {  };
        public IEnumerable<string> SameReference { get { return data; } } //this returns a reference to an unchanged object
        public IEnumerable<string> NewReference { get { return new List<string>(data); } } //this returns a reference to a new object
        //ObservableCollection<string> conventional is known but not the point of this question

        public event PropertyChangedEventHandler PropertyChanged;

        private void Raise(string propertyName)
        {
            if(null != PropertyChanged)
            {
                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
            }
        }

        public MainWindow()
        {
            this.DataContext = this;
            InitializeComponent();
        }

        private void Button_Click(object sender, RoutedEventArgs e)
        {
            data.Add("This is data.");
            Raise("SameReference"); //successful notify, ignored values
            Raise("NewReference"); //successful notify, processed values
        }
    }
}

回答1:

That is intentional behavior. If you want collections to update implement INotifyCollectionChanged (or use a class that already does, like ObservableCollection<T>).

来源：https://stackoverflow.com/questions/38072670/propertychanged-is-ignored-when-binding-to-ienumerable-where-reference-stays-the

标签

wpf

xaml

data-binding