WPF ListView SelectedItems绑定附加属性如何支持任意对象类型

原实现无法支持任意类型集合的核心原因有两个：

• 附加属性注册时硬编码了属性类型为ObservableCollection<Object>，而ObservableCollection<T>不支持协变，ObservableCollection<自定义业务类型>无法直接赋值给该类型的依赖属性，绑定会直接失效。
• 原实现仅支持控件到绑定源的单向同步，且没有做事件解绑，存在内存泄漏、默认集合实例跨控件共享的隐性bug。

将附加属性的注册类型改为非泛型IList接口（所有可绑定的泛型集合都实现了该接口），同时补全双向同步逻辑、循环触发防护、事件解绑逻辑即可。修改后的完整代码如下：

public class DisplaySelectedItems
{
    // 同步标记，防止双向同步时出现循环触发
    private static readonly Dictionary<DependencyObject, bool> _syncState = new Dictionary<DependencyObject, bool>();

    public static void SetSelectedItems(DependencyObject element, IList value)
    {
        if (element is not SfDataGrid && element is not ListView)
            throw new NotSupportedException("This property can be used only with SfDataGrid or ListView");
        element.SetValue(SelectedItemsProperty, value);
    }

    public static IList GetSelectedItems(DependencyObject element)
    {
        return (IList)element.GetValue(SelectedItemsProperty);
    }

    public static readonly DependencyProperty SelectedItemsProperty =
        DependencyProperty.RegisterAttached("SelectedItems", typeof(IList), typeof(DisplaySelectedItems), 
            new PropertyMetadata(null, OnSelectedItemsChanged));

    private static void OnSelectedItemsChanged(DependencyObject d, DependencyPropertyChangedEventArgs args)
    {
        // 解绑旧集合的监听事件
        if (args.OldValue is INotifyCollectionChanged oldCollection)
        {
            oldCollection.CollectionChanged -= OnSourceCollectionChanged;
        }

        // 针对不同控件类型绑定对应事件，先解绑旧事件避免重复订阅
        switch (d)
        {
            case SfDataGrid sfDataGrid:
                sfDataGrid.SelectedItems.CollectionChanged -= OnControlSelectedItemsChanged;
                sfDataGrid.Unloaded -= OnControlUnloaded;
                sfDataGrid.SelectedItems.CollectionChanged += OnControlSelectedItemsChanged;
                sfDataGrid.Unloaded += OnControlUnloaded;
                SyncFromControlToSource(d);
                break;
            case ListView listView:
                listView.SelectionChanged -= OnListViewSelectionChanged;
                listView.Unloaded -= OnControlUnloaded;
                listView.SelectionChanged += OnListViewSelectionChanged;
                listView.Unloaded += OnControlUnloaded;
                SyncFromControlToSource(d);
                break;
        }

        // 监听绑定源集合的变化，做反向同步
        if (args.NewValue is INotifyCollectionChanged newCollection)
        {
            newCollection.CollectionChanged += OnSourceCollectionChanged;
        }

        // 本地事件处理函数
        void OnControlSelectedItemsChanged(object sender, NotifyCollectionChangedEventArgs e) => SyncFromControlToSource(d);
        void OnListViewSelectionChanged(object sender, SelectionChangedEventArgs e) => SyncFromControlToSource(d);
        void OnControlUnloaded(object sender, RoutedEventArgs e)
        {
            // 控件卸载时解绑所有事件，避免内存泄漏
            if (d is SfDataGrid grid)
            {
                grid.SelectedItems.CollectionChanged -= OnControlSelectedItemsChanged;
                grid.Unloaded -= OnControlUnloaded;
            }
            if (d is ListView lv)
            {
                lv.SelectionChanged -= OnListViewSelectionChanged;
                lv.Unloaded -= OnControlUnloaded;
            }
            if (GetSelectedItems(d) is INotifyCollectionChanged collection)
            {
                collection.CollectionChanged -= OnSourceCollectionChanged;
            }
            _syncState.Remove(d);
        }
    }

    private static void OnSourceCollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
    {
        // 找到集合对应的目标控件，同步选中状态
        var target = _syncState.Keys.FirstOrDefault(ele => GetSelectedItems(ele) == sender);
        if (target == null || (_syncState.ContainsKey(target) && _syncState[target])) return;
        
        _syncState[target] = true;
        try
        {
            switch (target)
            {
                case SfDataGrid grid:
                    grid.SelectedItems.Clear();
                    foreach (var item in (IList)sender) grid.SelectedItems.Add(item);
                    break;
                case ListView lv:
                    lv.SelectedItems.Clear();
                    foreach (var item in (IList)sender) lv.SelectedItems.Add(item);
                    break;
            }
        }
        finally
        {
            _syncState[target] = false;
        }
    }

    private static void SyncFromControlToSource(DependencyObject d)
    {
        var sourceCollection = GetSelectedItems(d);
        if (sourceCollection == null || (_syncState.ContainsKey(d) && _syncState[d])) return;

        _syncState[d] = true;
        try
        {
            IList controlSelectedItems = d switch
            {
                SfDataGrid grid => grid.SelectedItems,
                ListView lv => lv.SelectedItems,
                _ => null
            };
            if (controlSelectedItems == null) return;
            
            sourceCollection.Clear();
            foreach (var item in controlSelectedItems) sourceCollection.Add(item);
        }
        finally
        {
            _syncState[d] = false;
        }
    }
}

• XAML中直接绑定对应业务类型的集合即可，比如ListView的条目源是ObservableCollection<User>，附加属性直接绑定同类型的ObservableCollection<User>选中项集合，无需转换为object类型集合。
• 绑定的选中项集合需要在ViewModel中提前初始化，不要传null值，否则同步逻辑无法执行。
• 修复后的实现支持双向同步：无论是用户在UI上修改选中状态，还是在代码中修改绑定的源集合，两边状态都会自动保持一致，同时解决了原实现的内存泄漏问题。

内容的提问来源于stack exchange，提问作者MElSawy