我正在尝试使用附加属性将窗口上的ObservableCollection绑定到ViewModel。由于调用了PropertyChangedCallback，绑定似乎可以工作，但是如果我调用GetMyProperty方法，它总是返回NULL。

MainWindow.xaml

<Window x:Class="AttachedOberservableCollectionTest.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:local="clr-namespace:AttachedOberservableCollectionTest"
        Loaded="Window_Loaded"
        Height="450" Width="800">
    <Window.DataContext>
        <local:ViewModel/>
    </Window.DataContext>
    
    <Grid>
        <local:MainWindow.MyProperty>
            <Binding Path="MyCollection" Mode="TwoWay" UpdateSourceTrigger="PropertyChanged"/>
        </local:MainWindow.MyProperty>
    </Grid>
</Window>

MainWindow.xaml.cs

using System;
using System.Collections.ObjectModel;
using System.Windows;

namespace AttachedOberservableCollectionTest
{
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }

        public static ObservableCollection<int> GetMyProperty(DependencyObject obj)
        {
            return (ObservableCollection<int>)obj.GetValue(MyPropertyProperty);
        }

        public static void SetMyProperty(DependencyObject obj, ObservableCollection<int> value)
        {
            obj.SetValue(MyPropertyProperty, value);
        }

        public static readonly DependencyProperty MyPropertyProperty =
            DependencyProperty.RegisterAttached("MyProperty", typeof(ObservableCollection<int>), typeof(MainWindow), new PropertyMetadata(null, MyPopertyChanged));

        private static void MyPopertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            var newCollection = (ObservableCollection<int>)e.NewValue;
            Console.WriteLine($"New collection has {newCollection.Count} values");
        }

        private void Window_Loaded(object sender, RoutedEventArgs e)
        {
            var collection = GetMyProperty(this);

            if (collection == null)
                Console.WriteLine("Attached property is null");
            else
                Console.WriteLine($"Attached poperty has {collection.Count} values");
        }
    }
}

ViewModel.cs

using System.Collections.ObjectModel;

namespace AttachedOberservableCollectionTest
{
    public class ViewModel
    {
        public ObservableCollection<int> MyCollection { get; set; } = new ObservableCollection<int>();

        public ViewModel()
        {
            MyCollection.Add(1);
            MyCollection.Add(2);
        }
    }
}

我得到的输出是:

New collection has 2 values
Attached property is null

visual studio中的xaml编辑器还为工具提示消息提供了值“System.Windows.Data.Binding”，该值的类型不是“System.Int32”，因此不能在此泛型集合中使用。参数名称:value。