using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using Microsoft.Xaml.Behaviors;

namespace SWS.Commons.Helper.Behaviours
{
    /// <summary>
    /// 让 WPF TreeView 支持 SelectedItem 双向绑定的行为类。
    /// 应用于 TreeView 后，可在 ViewModel 中直接使用绑定方式访问/设置选中项。
    /// </summary>
    public static class TreeViewSelectedItemBehavior
    {
        public static readonly DependencyProperty SelectedItemProperty =
            DependencyProperty.RegisterAttached(
                "SelectedItem",
                typeof(object),
                typeof(TreeViewSelectedItemBehavior),
                new FrameworkPropertyMetadata(
                    null,
                    FrameworkPropertyMetadataOptions.BindsTwoWayByDefault,
                    OnSelectedItemChanged));

        // 获取附加属性值
        public static object GetSelectedItem(TreeView treeView) =>
            treeView.GetValue(SelectedItemProperty);

        // 设置附加属性值
        public static void SetSelectedItem(TreeView treeView, object value) =>
            treeView.SetValue(SelectedItemProperty, value);

        // 属性变化时的事件处理
        private static void OnSelectedItemChanged(DependencyObject sender, DependencyPropertyChangedEventArgs e)
        {
            if (sender is TreeView treeView)
            {
                // 解耦旧事件处理器
                treeView.SelectedItemChanged -= OnTreeViewSelectedItemChanged;
                // 连接新事件处理器
                treeView.SelectedItemChanged += OnTreeViewSelectedItemChanged;
            }
        }

        // TreeView选择项变化时的处理
        private static void OnTreeViewSelectedItemChanged(object sender, RoutedPropertyChangedEventArgs<object> e)
        {
            var treeView = (TreeView)sender;
            // 更新附加属性值
            treeView.SetCurrentValue(SelectedItemProperty, e.NewValue);
        }
    }

}