WPF 使用附加属性来绑定ListBox的SelectedItems

 

ListBox的SelectedItems属性是只读属性，没法直接绑定。

一般的处理方式是在命令中通过命令参数传递到ViewModel里面。

现在通过附加属性来解决这个问题

效果

 

后台代码

using Microsoft.Toolkit.Mvvm.ComponentModel;
using Microsoft.Toolkit.Mvvm.Input;
using System;
using System.Collections;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Controls.Primitives;
using System.Windows.Input;

namespace MvvmToolkit学习
{
    public class DataItem
    {
        public ObservableCollection<string> Data { get; set; }

        public string Name { get; set; }

        public DataItem()
        {
            Data = new ObservableCollection<string>();
            Data.Add("Sun");
            Data.Add("Moon");
            Data.Add("Star");
        }
    }

    public class ListBoxHelper
    {
        // Using a DependencyProperty as the backing store for SelectedItems.  This enables animation, styling, binding, etc...
        public static readonly DependencyProperty SelectedItemsProperty =
            DependencyProperty.RegisterAttached("SelectedItems",
                typeof(IList),
                typeof(ListBoxHelper),
                new FrameworkPropertyMetadata(default(IList),
                    FrameworkPropertyMetadataOptions.BindsTwoWayByDefault,
                    OnSelectedItemsChanged));

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

        public static void SetSelectedItems(DependencyObject obj, IList value)
        {
            obj.SetValue(SelectedItemsProperty, value);
        }

        private static void OnlistBoxSelectionChanged(object sender, SelectionChangedEventArgs e)
        {
            IList dataSource = GetSelectedItems(sender as DependencyObject);
            //添加用户选中的当前项.
            foreach (var item in e.AddedItems)
            {
                dataSource.Add(item);
            }
            //删除用户取消选中的当前项
            foreach (var item in e.RemovedItems)
            {
                dataSource.Remove(item);
            }
        }

        private static void OnSelectedItemsChanged(DependencyObject target, DependencyPropertyChangedEventArgs e)
        {
            var listBox = target as ListBox;
            if ((listBox != null) && (listBox.SelectionMode == SelectionMode.Multiple))
            {
                if (e.OldValue != null)
                {
                    listBox.SelectionChanged -= OnlistBoxSelectionChanged;
                }
                IList collection = e.NewValue as IList;
                listBox.SelectedItems.Clear();
                if (collection != null)
                {
                    foreach (var item in collection)
                    {
                        listBox.SelectedItems.Add(item);
                    }
                    listBox.SelectionChanged += OnlistBoxSelectionChanged;
                }
            }
        }
    }

    internal class Test1ViewModel : ObservableObject
    {
        private RelayCommand addCmd;

        public ICommand AddCmd
        {
            get
            {
                if (addCmd == null)
                {
                    addCmd = new RelayCommand(PerformAddCmd);
                }

                return addCmd;
            }
        }

        public ObservableCollection<DataItem> DataItems { get; set; }
        public List<DataItem> SelectedItems { get; set; }
        public double Size { get; set; }

        public Test1ViewModel()
        {

//因为默认值是null所以不会进回调
//给附加属性一个非null值就可以了
//只有附加属性值改变的时候才会触发PropertyChanged，默认属性值是null，VM的值也是null，所以不触发

            SelectedItems = new List<DataItem>();//此处属性必须赋值，不可为null。。绕了很久的弯路
            DataItems = new ObservableCollection<DataItem>();
            DataItems.Add(new DataItem() { Name = "A" });
            DataItems.Add(new DataItem() { Name = "B" });
        }

        private void PerformAddCmd()
        {
            MessageBox.Show(string.Join("", SelectedItems.Select(s => s.Name)));
        }
    }
}

xaml

<Window
    x:Class="MvvmToolkit学习.Test1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:local="clr-namespace:MvvmToolkit学习"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:pu="clr-namespace:Panuon.UI.Silver;assembly=Panuon.UI.Silver"
    Title="Test1"
    Width="800"
    Height="450"
    d:DataContext="{d:DesignInstance Type={x:Type local:Test1ViewModel}}"
    mc:Ignorable="d">
    <Grid>
        <StackPanel Orientation="Vertical">
            <ListBox
                Width="200"
                Height="100"
                local:ListBoxHelper.SelectedItems="{Binding SelectedItems}"
                ItemsSource="{Binding DataItems}"
                SelectionMode="Multiple">
                <ListBox.ItemTemplate>
                    <DataTemplate DataType="{x:Type local:DataItem}">
                        <StackPanel Orientation="Horizontal">
                            <CheckBox IsChecked="{Binding Path=IsSelected, RelativeSource={RelativeSource AncestorType=ListBoxItem, Mode=FindAncestor}}"/>
                            <ContentControl Content="{Binding}"/>
                        </StackPanel>
                    </DataTemplate>
                </ListBox.ItemTemplate>
            </ListBox>

            <Button
                Width="200"
                Height="35"
                Command="{Binding AddCmd}"/>
            <DataGrid pu:DataGridHelper.SelectedItems="{Binding DataItems}"/>
        </StackPanel>
    </Grid>
</Window>