Binding SelectedItems

MultiSelectorHelper.cs

using System;
using System.Collections;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Controls.Primitives;

namespace DataGridView
{
    public class MultiSelectorHelper
    {
        #region Bindable SelectedItems

        public static IList GetBindableSelectedItems(DependencyObject obj)
        {
            return (IList)obj.GetValue(BindableSelectedItemsProperty);
        }

        public static void SetBindableSelectedItems(DependencyObject obj, IList value)
        {
            obj.SetValue(BindableSelectedItemsProperty, value);
        }

        public static readonly DependencyProperty BindableSelectedItemsProperty =
            DependencyProperty.RegisterAttached(
                "BindableSelectedItems",
                typeof(IList),
                typeof(MultiSelectorHelper),
                new PropertyMetadata(null)
            );

        #endregion

        #region Monitor SelectionChanged

        public static bool GetMonitorSelectionChanged(DependencyObject obj)
        {
            return (bool)obj.GetValue(MonitorSelectionChangedProperty);
        }

        public static void SetMonitorSelectionChanged(DependencyObject obj, bool value)
        {
            obj.SetValue(MonitorSelectionChangedProperty, value);
        }

        public static readonly DependencyProperty MonitorSelectionChangedProperty =
            DependencyProperty.RegisterAttached(
                "MonitorSelectionChanged",
                typeof(bool),
                typeof(MultiSelectorHelper),
                new PropertyMetadata(false, MonitorSelectionChangedPropertyChangedCallback)
            );

        private static void MonitorSelectionChangedPropertyChangedCallback(
            DependencyObject d,
            DependencyPropertyChangedEventArgs e
        )
        {
            if (d is not MultiSelector selector)
                throw new InvalidOperationException();

            if ((bool)e.NewValue)
                selector.SelectionChanged += OnSelectionChanged;
            else
                selector.SelectionChanged -= OnSelectionChanged;
        }

        private static void OnSelectionChanged(object sender, SelectionChangedEventArgs e)
        {
            var selector = (MultiSelector)sender;
            SetBindableSelectedItems(selector, selector.SelectedItems);
            selector.GetBindingExpression(BindableSelectedItemsProperty).UpdateSource();
        }

        #endregion
    }
}

SelectedItemsBehavior.cs

using Microsoft.Xaml.Behaviors;
using System.Collections;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Controls.Primitives;

namespace DataGridView
{
    public class SelectedItemsBehavior : Behavior<MultiSelector>
    {
        protected override void OnAttached()
        {
            base.OnAttached();

            AssociatedObject.SelectionChanged += OnSelectionChanged;
        }

        protected override void OnDetaching()
        {
            base.OnDetaching();

            AssociatedObject.SelectionChanged -= OnSelectionChanged;
        }

        private void OnSelectionChanged(object sender, SelectionChangedEventArgs e)
        {
            var name = nameof(OnSelectionChanged);
            var func = (int x) => x.ToString();
            var selector = (MultiSelector)sender;
            BindableSelectedItems = selector.SelectedItems;
            selector.GetBindingExpression(BindableSelectedItemsProperty)?.UpdateSource();
        }

        #region Bindable SelectedItems

        public IList BindableSelectedItems
        {
            get { return (IList)GetValue(BindableSelectedItemsProperty); }
            set { SetValue(BindableSelectedItemsProperty, value); }
        }

        public static readonly DependencyProperty BindableSelectedItemsProperty =
            DependencyProperty.Register(
                nameof(BindableSelectedItems),
                typeof(IList),
                typeof(SelectedItemsBehavior),
                new PropertyMetadata(null)
            );

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

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

        public static readonly DependencyProperty MyPropertyProperty =
            DependencyProperty.RegisterAttached(
                "MyProperty",
                typeof(int),
                typeof(SelectedItemsBehavior),
                new PropertyMetadata(0)
            );

        #endregion
    }
}

我按照视频上写法 发现里面获取绑定一直为NULL，让ChatGpt 优化了一下也是一直为空。找不到问题出现再那里

` public class DataGridSelectItemsBehavior : Behavior
{
public static readonly DependencyProperty MySlectItemsProperty =
DependencyProperty.Register("MySlectItems", typeof(IList), typeof(DataGridSelectItemsBehavior), new PropertyMetadata(null));

  public static readonly DependencyProperty SelectIndexProperty =
      DependencyProperty.Register("SelectIndex", typeof(int), typeof(DataGridSelectItemsBehavior), new PropertyMetadata(-1));

  public IList MySlectItems
  {
      get { return (IList)GetValue(MySlectItemsProperty); }
      set { SetValue(MySlectItemsProperty, value); }
  }

  public int SelectIndex
  {
      get { return (int)GetValue(SelectIndexProperty); }
      set { SetValue(SelectIndexProperty, value); }
  }

  protected override void OnAttached()
  {
      base.OnAttached();
      AssociatedObject.SelectionChanged += AssociatedObject_SelectionChanged;
  }

  private void AssociatedObject_SelectionChanged(object sender, SelectionChangedEventArgs e)
  {
      var dataGrid = sender as DataGrid;
      if (dataGrid != null)
      {
          MySlectItems = dataGrid.SelectedItems;
          SelectIndex = dataGrid.SelectedIndex;
          var s = dataGrid.GetBindingExpression(MySlectItemsProperty);
      }

  }

  protected override void OnDetaching()
  {
      base.OnDetaching();
      AssociatedObject.SelectionChanged -= AssociatedObject_SelectionChanged;
  }

}`

`

        <i:Interaction.Behaviors>

            <local:DataGridSelectItemsBehavior MySlectItems="{Binding UserSelectedItems1, Mode=TwoWay}" SelectIndex="{Binding Select, Mode=TwoWay}" />
        </i:Interaction.Behaviors>
        <DataGrid.Columns>
            <DataGridTextColumn Binding="{Binding Index}" Header="序号" />
            <DataGridTextColumn Binding="{Binding Age}" Header="年龄" />
            <DataGridTextColumn Binding="{Binding Salary}" Header="工资" />
            <DataGridTextColumn Binding="{Binding Phone}" Header="电话" />
            <DataGridTextColumn Binding="{Binding Address}" Header="住址" />

        </DataGrid.Columns>

    </DataGrid>`

我按照视频上写法 发现里面获取绑定一直为 NULL，让 ChatGpt 优化了一下也是一直为空。找不到问题出现再那里

UpdateSource 应按照如下写法，但其实是不需要的。
//var bindingExp = BindingOperations.GetBindingExpression(this, BindableSelectedItemsProperty);
//bindingExp?.UpdateSource();

VM 中绑定的值类型需要是 IList，且不能是泛型的。